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Neurotransmission

Contents by Research Area:• Dopaminergic Transmission• Glutamatergic Transmission• Opioid Peptide Transmission• Serotonergic Transmission• Chemogenetics

DelphiniumDelphinium A source of Methyllycaconitine

Product Guide | Edition 1

Tocris Product Guide Series

2 |

Neurotransmission Research

Contents

IntroductionNeurotransmission, or synaptic transmission, refers to the passage of signals from one neuron to another, allowing the spread of information via the propagation of action potentials. This process is the basis of communication between neurons within, and between, the peripheral and central nervous systems, and is vital for memory and cognition, muscle contraction and co-ordination of organ function. The following guide outlines the principles of dopaminergic, opioid, glutamatergic and serotonergic transmission, as well as providing a brief outline of how neurotransmission can be investigated in a range of neurological disorders.

Included in this guide are key products for the study of neurotransmission, targeting different neurotransmitter systems. The use of small molecules to interrogate neuronal circuits has led to a better understanding of the under-lying mechanisms of disease states associated with neurotransmission, and has highlighted new avenues for treat-ment. Tocris provides an innovative range of high performance life science reagents for use in neurotransmission research, equipping researchers with the latest tools to investigate neuronal network signaling in health and disease. A selection of relevant products can be found on pages 23-33.

Page

Principles of Neurotransmission 3

Dopaminergic Transmission 5

Glutamatergic Transmission 6

Opioid Peptide Transmission 8

Serotonergic Transmission 10

Chemogenetics in Neurotransmission Research 12

Depression 14

Addiction 18

Epilepsy 20

List of Acronyms 22

Neurotransmission Research Products 23

Featured Publications and Further Reading 34

Key Neurotransmission Research Products

Box Number Title Page

Box 1 Dopaminergic Transmission 5

Box 2 Glutamatergic Transmission 7

Box 3 Opioid Transmission 9

Box 4 Serotonergic Transmission 11

Box 5 Chemogenetic Compounds: DREADD ligands and PSEMs

13

Box Number Title Page

Box 6 Antidepressants 15

Box 7 Ketamine and its Metabolites 17

Box 8 Addiction 19

Box 9 Epilepsy 20

NEUROTRANSMISSION RESEARCH

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Principles of NeurotransmissionThe majority of neurotransmission occurs across chemical syn-apses, where an endogenous neurotransmitter is released by the presynaptic neuron and detected by receptors on the post-synaptic neuron (Figure 1). Neurotransmitters can be broadly split into three categories; amino acids including glutamate and glycine, amines including dopamine (DA), serotonin (5-HT) and norepinephrine (NE), and peptides such as dynorphin, the enkephalins and neuropeptide Y.

While the amino acids glutamate and glycine are found in all cells of the body, other neurotransmitters are only synthe-sized by neurons. Following synthesis, neurotransmitters are taken up and stored in synaptic vesicles, ready for release. The release of a neurotransmitter is triggered by the arrival of action potentials in the axon terminal of the presynaptic neuron, open-ing voltage-gated Ca2+ channels and allowing influx of ions. The resulting elevation in intracellular Ca2+ concentration causes synaptic vesicles to merge with the presynaptic mem-brane, releasing the neurotransmitter into the synaptic cleft by exocytosis.

Neurotransmitters cross the synaptic cleft and bind to their spe-cific receptors. These maybe ligand-gated ion channels (LGICs) or G protein-coupled receptors (GPCRs), with some neuro-transmitters having receptors in both categories. Binding of a neurotransmitter to a LGIC causes a conformational change in the structure of the protein, allowing the passage of ions through the channel. Passage of ions through channels that are selective for positively-charged cations results in depolariza-tion of the postsynaptic membrane and initiation of an action potential in the postsynaptic neuron. In contrast, passage of ions through negatively-charged, anion selective channels results in hyperpolarization of the postsynaptic membrane, so inhibiting action potential initiation. Binding of a neuro-transmitter to a GPCR results in the activation of G proteins, which are then able to act on enzymes to modulate intracellular signaling pathways. The end result of this is the modulation of activity of other proteins, including ion channels and enzymes.

Once a neurotransmitter has bound to its receptor, it is cleared from the synaptic cleft to allow another wave of synaptic

This simplified schematic shows the main events during dopaminergic, glutamatergic, opioid peptide and serotonergic neurotransmission. DA and 5-HT are both biogenic amines that are derived from amino acids, while glutamate itself is an amino acid and opioid peptides are cleaved from precursor proteins. All neurotransmitters undergo exocytosis from the presynaptic membrane and cross the synaptic cleft where they bind to their specific receptors. These receptors may be ligand gated ion channels, such as ionotropic glutamate receptors, or G protein-coupled receptors, such as all subtypes of opioid receptor. Passage of ions through a ligand gated ion channel alters the excitability of a neuron. The action of neurotransmitters at GPCRs alters intracellular signaling pathways, with the specific pathway being dependent on the G protein-coupled to the receptor.

Figure 1 | Principles of Neurotransmission

Presynaptic neuron Postsynaptic neuron

Precursor proteins

Opioidproteins

Glu

Glu

Gi/0

Gs

AC

cAMP

ATP

PLC

Mg2+

5-HT3

NMDARs

AMPARs andKainate receptors

5-HT1,5D2,3,4

Opioid receptorsGroup II and III mGluRs

IP3

Ca2+

Ca2+

Na+

CaMK

CaMK

Increasedneuronal

excitability

DAG PKC

PKA

Gq/11

PDE(–)

(–)

(–)

5-HT

DA

DAT

SERT

5-HT4,6,7

D1.5

5-HT2Group I mGluRs


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Detected in immersion-fixed paraffin-embedded sections of human brain (substantia nigra) using a Goat Anti-Human/Mouse/Rat DDC Antigen Affinity-Purified Polyclonal Antibody (R&D Systems, Cat. No. AF3564). The tissue was stained using the Anti-Goat HRP-DAB Cell & Tissue Staining Kit (R&D Systems, Cat. No. CTS008; brown) and counterstained with hematoxylin (blue. Tocris, Cat. No. 5222). Specific staining was localized to the neuronal cytoplasm.

D1R detected in immersion-fixed paraffin-embedded sections of human brain (caudate nucleus) using a Mouse Anti-Human Dopamine D1R Monoclonal Antibody (R&D Systems, Cat. No. MAB8276). The tissue was stained using the Anti-Mouse HRP-DAB Cell & Tissue Staining Kit (R&D Systems, Cat. No. CTS002; brown) and counterstained with hematoxylin (blue. Tocris, Cat. No. 5222). Specific staining was localized to the neuronal cytoplasm.

DAT1 detected in immersion-fixed sections of human brain (substantia nigra) using a Mouse Anti-Human/Mouse/Rat DAT1 Monoclonal Antibody (Novus Biologicals, Cat. No. NBP2-46649). The tissue was stained using HRP and DAB (brown) and counterstained with hematoxylin (blue. Tocris, Cat. No. 5222). Specific staining was localized to the dopamine neuron nuclei and fibres.

Figure 2 | DDC in Human Brain Figure 3 | D1R in Human Brain Figure 4 | DAT1 in Human Brain

transmission. Neurotransmitter molecules are taken up by the presynaptic neuron, or by other cell types such as astrocytes, via specific reuptake transporters. Neurotransmitters may then be metabolized to be reused for further production, or they can be recycled into synaptic vesicles.

The strength of the synaptic connection between two neurons depends on a range of factors. These include the number of individual synapses between two neurons, the probability of neurotransmitter release at the presynaptic membrane and the size of the post-synaptic potential induced by binding of the neurotransmitter to its receptor. The presence of neurotrans-mitter receptors on the pre-synaptic membrane also regulates the release of neurotransmitters, through both positive and negative feedback loops. Synaptic connection strength is a key factor in cognitive processes including memory formation.

Action Potentials

An action potential is the signal that conveys information along a neuron and is also the trigger for release of a neurotrans-mitter at a synapse. Physically, an action potential is the rapid reversal of the resting membrane potential, caused by opening and closing of voltage-gated ion channels. At rest, the cytosol of a neuron is negatively charged (polarized) with respect to extracellular fluid, due to the distribution of ions across the cell membrane.

An action potential is initiated by the opening of voltage-gated Na+ channels (Nav channels) allowing influx of Na+ down its

concentration gradient. This depolarizes the cell membrane past the threshold for action potential initiation. As Nav chan-nels become inactivated, preventing the flow of Na+, voltage-gated potassium channels (Kv channels) open allowing the efflux of K+. This causes repolarization of the cell membrane, as the balance of ion movement across the membrane leads to the cytosol being more negatively charged than extracellular fluid. When Kv channels are open the cell membrane is highly permeable to K+, but permeability to Na+ is low as Nav channels are still inactivated. This leads to a period of hyperpolarization until Kv channel close, and the resting membrane potential is re-established.

Propagation of an action potential occurs as a wave of depolar-ization that spreads along an axon. When an area of the mem-brane becomes depolarized, it opens neighboring Nav channels, which then allow depolarization of that section of the mem-brane. The inactivation of Nav channels in the preceding sec-tion of membrane ensures that an action potential travels in only one direction alone an axon. Some axons in the central nervous system have a sheath around them, composed of mye-lin, which acts as an electrical insulator. Nav and Kv channels are localized on gaps in the myelin sheath, known as nodes of Ranvier. Myelination increases that speed of action potential propagation as the action potential effectively ‘hops’ along an axon, occurring only at nodes of Ranvier in a process known as saltatory conduction.


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Dopaminergic Transmission

DA is the major catecholamine neurotransmitter in the mam-malian brain and is involved in a range of functions includ-ing locomotion, neuroendocrine secretion, cognition and emotion. It is metabolized from the amino acid tyrosine in a two-step process. First the conversion of L-tyrosine to levo-dopa (L-DOPA) is catalyzed by tyrosine hydroxylase (TH), then L-DOPA is converted to DA by DOPA decarboxylase (DDC; Figure 2). TH is a marker for neurons expressing catecholamine

neurotransmitters, including norepinephrine and epinephrine, and its activity is a rate-limiting step in catecholamine synthe-sis. Following synthesis, DA is released at the synaptic cleft and binds to its receptors on the postsynaptic membrane.

All DA receptors are GPCRs and they can be split into two families based on their structure, function and pharmaco-logical properties: D1-like receptors and D2-like receptors. The D1-like receptors, D1R (Figure 3) and D5R, are coupled to the G protein Gs and activate adenylyl cyclase to increase the intra-cellular concentration of the second messenger cyclic adenosine monophosphate (cAMP). The D2-like receptors, D2R, D3R and D4R, are coupled to the Gi/o pathway, which directly inhibits the formation of cAMP by inhibiting adenylyl cyclase.

The actions of DA and other catecholamines in the synaptic cleft are terminated by their reuptake into the presynaptic neu-rons, via selective Na+-dependent transporters; DA is taken up by the dopamine transporter (DAT; Figure 4). Once returned to synaptic vesicles by the vesicular monoamine transporters (VMATs), DA may be recycled for release or broken down by monoamine oxidase (MAO), located on the outer mitochon-drial membrane.

Products by Category Page

Adenylyl Cyclase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25cAMP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26Catechol O-Methyltransferase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27Decarboxylases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27Dopamine D1-like Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27Dopamine D2-like Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28Dopamine Receptors: Non-selective Compounds . . . . . . . . . . . 28Dopamine Transporters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28Monoamine Oxidase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31Vesicular Monoamine Transporters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

HO

HO

CO2H

NHNH2Me

Box 1: Dopaminergic Transmission

(S)-(-)-Carbidopa (0455)Aromatic L-amino acid decarboxylase inhibitor

NO2

OH

OH

O2N

OR-486 (0483)COMT inhibitor

Ru2+PMe3

NH2

N

N

N

N

OH

OH

RuBi-Dopa (4932)Caged dopamine; exhibits two-photon sensitivity

ON

N

GBR 12783 (0513)Potent and selective DA uptake inhibitor

N

OH

OH

Cl

SKF 82958 (5719)D1 agonist

N

HN O

N

NC

SB 277011A (4207)Selective D3 antagonist

NH

N

Me

LE 300 (1674)Potent and selective D1 antagonist

Box 1: Dopaminergic TransmissionSee pages 23-33 for a full list of targets and related products


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Glutamate is an amino acid and is the most abundant excita-tory neurotransmitter in the nervous system. Under healthy conditions, enough glutamate is obtained from the diet and it does not need to be synthesized, however it can be synthe-sized from α-ketoglutarate, a product of the citric acid cycle. Two types of glutamate receptor exist: metabotropic glutamate receptors (mGluRs), which are GPCRs, and ionotropic gluta-mate receptors, which are LGICs. mGluRs are encoded by a single gene and are composed of an extracellular region con-taining the glutamate binding site, a transmembrane region, and an intra cellular region that is coupled to a G protein. There are three subtypes of mGluRs based on receptor structure and physiological activity. Group I mGluRs are primarily located on postsynaptic membranes and are coupled to the Gq/11 pathway and activation of phospholipase C (PLC). In contrast, group II and group III mGluRs are mainly located on the presynaptic membrane, are coupled to the Gi/o pathway and prevent the formation of cAMP, leading to presynaptic inhibition.

Ionotropic GluRs (iGluRs, Figure 6) are LGICs that are tetra-mers formed by homo- or hetero-oligomeric assembly of sub-units, all of which are encoded by individual genes. The specific combination of subunits determines the activity of specific ago-nists and antagonists at iGluRs. They are divided into three subgroups based on pharmacology and sequence similarity, and are named for the agonists that selectively bind to them. AMPA receptors are the most commonly found receptor in the nervous system where they mediate fast synaptic transmis-sion. They are composed of subunits designated GluA1, GluA2, GluA3 and GluA4, and may also be associated with transmem-brane AMPA receptor regulatory proteins (TARPs) as auxiliary subunits. Kainate receptors modulate neurotransmission and can be located pre- or postsynaptically. Like AMPA recep-tors, they are composed of subunits designated GluK1, GluK2, GluK3, GluK4 and GluK5. NMDA receptors have a critical role in synaptic plasticity and are composed of subunits designated

GluN1, GluN2A-D and GluN3A or B. Alternative splicing of the GluN1, GluN2 and GluN3A subunits add to the heterogeneity of NMDA receptors.

AMPA and Kainate receptors have a simple ligand-gated mechanism of action, however the gating of NMDARs is more complex. The opening and closing of NMDARs requires the binding of D-serine (Tocris, Cat. No. 0226) and glycine (Tocris, Cat. No. 0219) as well as glutamate. Additionally, the flow of ions through NMDARs is mediated by the binding of Mg2+ or Zn2+ to specific sites in the receptor. Only upon depolarization of the cell membrane, displacing Mg2+/Zn2+, does the influx of Na+ and Ca2+ and the efflux of K+ occur.

Following receptor activation, glutamate is released into the synaptic cleft from where it is taken up into neurons and glia by glutamate transporters, also known as excitatory amino acid transporters (EAATs). The EAAT family has five mem-bers, although EAAT2 expressed on glia is responsible for most glutamate reuptake in the central nervous system. Once taken up into glia, glutamate is converted into glutamine, which is transported back into presynaptic neurons where it is converted into glutamate once more for further synaptic transmission. Glutamate is packaged into synaptic vesicles by vesicular glutamate transporters (VGLUTs; Figure 5).


Adenylyl Cyclase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25AMPA Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25cAMP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26Glutamate Transporters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29Kainate Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30Metabotropic Glutamate Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30NMDA Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32Phospholipase C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

VGLUT2 detected in immersion-fixed paraffin-embedded sections of cerebellum using a Mouse Anti-Human/Mouse/Rat VGLUT2 Monoclonal Antibody (Novus Biologicals, Cat. No. NBP2-46641). The tissue was stained using HRP and DAB (brown) and counterstained with hematoxylin (blue. Tocris, Cat. No. 5222). Specific staining was localized to glutamatergic synapses in the molecular and granular layers of the cerebellum.

Figure 5 | VGLUT2 in Human Brain

Glutamatergic Transmission


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A) GluR1 (AMPA receptor subunit) was detected in immersion-fixed SK-N-BE human neuroblastoma cells using a Mouse Anti-Rat GluR1 Monoclonal Antibody (Novus Biologicals, Cat. No. NBP2-22399). The cells were stained using a ATTO 488-conjugated goat anti-mouse secondary antibody (green). The cells were also stained for F-Actin (Texas Red®-X phalloidin; red) and counterstained with DAPI (blue. Tocris, Cat. No 5748). Specific staining was localized to the cell membrane and cell junctions. B) KA2 (Kainate receptor subunit) was detected in immersion-fixed, paraffin-embedded sections of human brain cortex using a Goat Anti-Human KA2/GRIK5/Glutamate Receptor KA2 Antigen Affinity-Purified Polyclonal Antibody (Novus Biologicals, Cat. No. NBP1-36959). The tissue was stained using alkaline phosphatase-streptavidin and chromogen (red) and counterstained with hematoxylin (blue. Tocris, Cat. No. 5222).

Figure 6 | Glutamate Receptor Expression

A B

Box 2: Glutamatergic Transmission

OMe

NO2

N

O

CO2H

NH2

O2N

MDNI-caged-L-glutamate (5785)Stable photoreleaser of L-glutamate

O

HN O

N

N

N N

NN

GT 949 (6578)Potent and selective positive allosteric modulator of EAAT2

CO2H

H

H2N

PO(OH)2

L-AP4 (0103)Selective group III mGlu agonist

Me

HN

(+)-MK 801 (0924)Non-competitive NMDA antagonist;

acts at ion channel site

NH

Me CO2H

CO2H

Kainic acid (0222)Kainate agonist; excitant and neurotoxin

N

N O-

O-

H2NO2S

O2N

2Na+

NBQX disodium salt (1044)Potent AMPA antagonist; more water soluble

form of NBQX (Cat. No. 0373)

NH2

PO(OH)2H

HO2C

D-AP5 (0106)Potent and selective NMDA antagonist;

more active form of DL-AP5 (Cat. No. 0105)

O

NaO2C

H

CO2NaH2N

LY 341495 disodium salt (4062)Potent and selective group II mGlu antagonist;disodium salt of LY 341495 (Cat. No. 1209)

Box 2: Glutamatergic TransmissionSee pages 23-33 for a full list of targets and related products


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pathways. The highest expression of the δ opioid receptor (DOR) is found in the basal ganglia and neocortical brain regions, while the κ opioid receptor (KOR) is widely distributed throughout the brain, including the prefrontal cortex, substan-tia nigra, amygdala and hippocampus. The µ opioid receptor (MOR) exists on presynaptic membranes in the periaqueductal gray and the dorsal horn of the spinal cord. The NOP receptor (nociceptin/orphanin FQ receptor) is also widely expressed in the brain and specifically binds nociceptin (Figure 7).

In general, endogenous opioids are not highly selective for one specific type of opioid receptor, due to the extensive similarities in receptor structure, function and intracellular signaling pathways. Also opioid receptors can form homo- and heteromeric complexes with each other, and with non-opioid receptors, which can change their response to a specific opi-oid peptide. These physical interactions between receptors are key to their pharmacological and physiological properties. All opioid peptides are broken down following receptor binding by peptidases. For example, enkephalins are broken down into inactive metabolites by two zinc metalloproteases; neprilysin and aminopeptidase N.

Endogenous opioid peptides are released from precursor proteins by proteolytic cleavage, and act at opioid receptors with differing selectivity. Proenkephalin is cleaved to release Met-enkephalin, and to a lesser extent Leu-enkephalin. Leu-enkephalin is predominantly cleaved from prodynorphin, along with dynorphin A and dynorphin B. Pro-opiomelanocortin is cleaved to release β-endorphin, the largest endogenous opioid peptide, while the more recently discovered nociceptin is cleaved from pronociceptin.

All opioid receptors are GPCRs coupled to the Gi/o pathway and so inhibit the formation of cAMP and its downstream signaling

Opioid Peptide Transmission


Adenylyl Cyclase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25cAMP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26δ Opioid Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28κ Opioid Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30µ Opioid Receptors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31NOP Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32Opioids Receptors: Non-selective Compounds . . . . . . . . . . . . . . . . 32

A) NOP (OPRL1) was detected in fixed sections of rat cingulate cortex using using a Rabbit Anti-Human/Mouse/Rat ORL1/OPRL1 Antigen Affinity-Purified Polyclonal Antibody (Novus Biologicals, Cat. No. NBP2-21065). The tissue was stained (green) and counterstained with DAPI (blue. Tocris, Cat. No 5748). B) MOR was detected in perfusion-fixed frozen sections of rat spinal cord using a Rabbit Anti-Rat μ Opioid R/OPRM1 Monoclonal Antibody (R&D Systems, Cat. No. MAB8629). The tissue was stained using the NorthernLights™ 557-Conjugated Anti-Rabbit IgG Secondary Antibody (R&D Systems, Cat. No. NL004; red) and counterstained with DAPI (blue. Tocris, Cat. No 5748). Specific staining was localized to the dorsal horn. C) KOR detected in immersion-fixed paraffin-embedded sections of human medulla using a Mouse Anti-Human KOR Monoclonal Antibody (R&D Systems, Cat. No. MAB38951). Before incubation with the primary antibody, tissue was subjected to heat-induced epitope retrieval using Antigen Retrieval Reagent-Basic (R&D Systems, Cat. No. CTS013). The tissue was stained with the Anti-Mouse HRP-DAB Cell & Tissue Staining Kit (R&D Systems, Cat. No. CTS002; brown) and counterstained with hematoxylin (blue. Tocris, Cat. No. 5222).

Figure 7 | Opioid Receptors

A B C


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Box 3: Opioid Transmission

OO NH OH

HO

NOH

N

HO

nor-Binaltorphimine (0347)Selective κ antagonist

(and enantiomer)

NMe

N OCl

Cl

(±)-U-50488 (0495)Selective κ agonist

HO

OH

O

N

NHH

O

CO2Me

β-Funaltrexamine (0926)Irreversible and selective μ antagonist

Tyr-D-Ala-Gly-NMe-Phe-Gly-ol

DAMGO (1171)Selective μ agonist

Et2N

O

OMe

H

N

N

Me

Me

SNC 80 (0764)Highly selective non-peptide δ agonist

(and enantiomer)

NN N

O

OH

(±)-J 113397 (2598)Potent and selective NOP antagonist

N

OHO O

OH

Naloxone (0599)Non-selective opioid antagonist

Box 3: Opioid TransmissionSee pages 23-33 for a full list of targets and related products

Scientific ReviewsProduct Guides & Listings Life Science Posters

• G-Protein Coupled Receptors• Ion Channels • Neurodegeneration• Pain Research

• Learning and Memory• Pain• Epilepsy• Depression

• Nicotinic ACh Receptors• 5-HT Receptors• GABA Receptors• Dopamine Receptors

Life Science Literature from TocrisTocris provides a wide range of scientific literature, including the following titles:

For a complete selection of Tocris literature please visit www.tocris.com/literature.php


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Serotonergic Transmission

5-HT is an amine neurotransmitter derived from the amino acid tryptophan, by tryptophan hydroxylase (TPH; Figure 8) and 5-HTP decarboxylase.

Once released into the synaptic cleft, 5-HT binds to its recep-tors. There are seven families of 5-HT receptors (Figure 9). 5-HT1, 5 receptors are GPCRs, coupled to the Gi/o pathway and so inhibit the formation of cAMP. In contrast, 5-HT4, 6, 7 recep-tors are coupled to the Gs pathway and so increase the produc-tion of cAMP. 5-HT2 receptors are coupled to the Gq/11 pathway and activate PLC, which hydrolyzes phosphatidylinositol (PIP2) to diacylglycerol (DAG) and inositol triphosphate (IP3). The only 5-HT receptor that is not a GPCR is the 5-HT3 receptor, which is a cation selective LGIC.

Like DA, following binding to its receptor 5-HT is taken up into neurons via a selective transporter, SERT. It can then be broken down by MAO or recycled for further synaptic transmission via repackaging into synaptic vesicles by VMATs.


5-HT Transporters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235-HT1 Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235-HT2 Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235-HT3-7 Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Adenylyl Cyclase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25cAMP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26Hydroxylases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30IP3 Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30Monoamine Oxidase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31Phospholipase C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32Vesicular Monoamine Transporters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

TPH-1 detected in perfusion-fixed frozen sections using a Goat Anti-Human TPH-1 Antigen Affinity-Purified Polyclonal Antibody (R&D Systems, Cat. No. AF5276). The tissue was stained using the NorthernLights™ 557-Conjugated Donkey Anti-Goat IgG Secondary Antibody (R&D Systems, Cat. No. NL001; red) and counterstained with DAPI (blue. Tocris, Cat. No 5748). Specific staining was localized to neurons.

A) 5-HT1F was detected in immersion-fixed paraffin-embedded sections using a Rabbit Anti-Human Antigen Affinity-Purified 5-HT1F Antibody (Novus Biologicals, Cat. No. NBP1-02371). The tissue was stained using alkaline phosphatase-streptavidin and chromogen (red) and counterstained with hematoxylin (blue. Tocris, Cat. No. 5222). B) 5-HT2C was detected in immersion-fixed paraffin-embedded sections using a Mouse Anti-Human 5-HT2C Monoclonal Antibody (R&D Systems, Cat. No. MAB5764). Before incubation with the primary antibody, the tissue was subjected to heat-induced epitope retrieval using Antigen Retrieval Reagent-Basic (R&D Systems, Cat. No. CTS013). The tissue was stained using the Anti-Mouse HRP-DAB Cell & Tissue Staining Kit (R&D Systems, Cat. No. CTS002; brown) and counterstained with hematoxylin (blue. Tocris, Cat. No. 5222). Specific staining was localized to neuronal cell bodies and processes.

A B

Figure 9 | 5-HT Receptors in the Human Brain Cortex

Figure 8 | TPH-1 in Rat Brain


www.tocris.com | 11

Box 4: Serotonergic Transmission

NHMe

O

F3C

Fluoxetine (0927)5-HT reuptake inhibitor

O N

NH

NH

CP 94253 (1317)Potent and selective 5-HT1B agonist

O

O

NNHSO2MeOMeN

H

F

GR 125487 (1658)Potent and selective 5-HT4 antagonist; active in vivo

F

N

N

H2N

RS 127445 (2993)High affinity and selective 5-HT2B antagonist

RuPMe3

NH2

N

N

N

N

.2PF6-

NH

OH

2+

RuBi-5-HT (3856)RuBi-caged serotonin

N

MeO

S

HN

NH

OMe

Cl

Cl

O O

SB 399885 (3189)Potent and selective 5-HT6 antagonist

NH

OO

MeN

Tropisetron (2459)Potent 5-HT3 antagonist; also α7 nAChR partial agonist

N

NN

OMe

N

O

WAY 100635 (4380)Potent 5-HT1A antagonist; also D4 agonist

Box 4: Serotonergic TransmissionSee pages 23-33 for a full list of targets and related products

Detection of Neurotransmitters in vivo with RNAscope®

Identification, visualization and characterization of specific cell types within the nervous system is difficult. RNAscope® in situ hybridization assay (ISH) (from ACD) can be used for the detection of RNA in the central and peripheral nervous system. The probes used are highly specific and sensitive with advanced signal amplification allowing visualization of single RNA transcripts. This enables researchers to detect RNA expression associated with proteins for which there are no reliable antibodies. RNAscope® ISH can be used for characterization of cell types, validation of genetic modifications, validation of mRNA expression and for determining subcellular localization of mRNA expression.

Figure 10 | DA Receptors in the Mouse Striatum DA receptors were detected using RNAscope multiplexing fluorescent ISH in fresh frozen mouse striatum, DAPI counterstaining. Two distinct populations of neurons expressing either D1R (Drd1, red) or D2R (Drd2, green) were identified. Areas indicated by green and red arrows are shown at higher magnification in the right hand panels.


12 |

Chemogenetics in Neurotransmission ResearchMajor advances in neuroscience methods have allowed researchers to selectively manipulate neural systems in awake animals, with two key techniques emerging; optogenetics and chemogenetics. Chemogenetic experiments require the intro-duction of genetically engineered receptors or ion channels into specific brain areas, via viral vector expression systems. Ligands, that are inert except for their specific action at those receptors/ion channels, are then administered. Binding of the ligand to its target initiates changes in downstream intracel-lular signaling pathways or opening of an ion channel pore, enabling controlled activation or inhibition of neuronal activ-ity, depending on the specific receptor/ion channel and ligand used. Similarly, optogenetics allows the modulation of neuronal activity via expression of light-sensitive ion channels. However, activation or inhibition of neuronal activity is initiated by implanted fibre optics, rather than small molecules.

Chemogenetic manipulation of neuronal activity can be achieved through genetically modified GPCRs known as DREADDs (Designer Receptors Activated by Designer Drugs; Figure 11) or though chimeric ion channels known as PSAMs (Pharmacologically Selective Actuator Modules). The binding of DREADD ligands to Gαq-DREADDs, such as hM3Dq, provokes neuronal firing, whereas binding to Gαi-DREADDs, such as hM4Di results in inhibition of neuronal activity. PSAMs containing the ion pore domain of cation selective channels, such as 5-HT3, result in neuronal activa-tion upon binding of a PSEM (Pharmacologically Selective Effector Molecule). In contrast, PSAMs containing the ion pore domain of an anion selective channel, such as the glycine receptor, are inhibitory.

Gαq

GαqGαi

Gαi

Clozapine N-oxide 2HCl (#6329)DREADD agonist 21 (#5548) Salvinorin B (#5611)

KORD

GPCR Chemogenetics: DREADDs

hM1Dq, hM5Dq

hM3Dq

hM4Di

Activation

Drug action

Inhibition

PLC

IP3 DAG

Ca2+ PKC

AC

cAMP ATP

PKA EPAC

Activate neuronal activity Inhibit neuronal activity

Figure 11 | Mechanism of action of DREADD ligands

Binding of DREADD ligands to Gαq-DREADDs provokes neuronal firing, whereas binding to Gαi-DREADDs results in inhibition of neuronal activity. Clozapine N-oxide dihydrochloride and DREADD agonist 21 are non-selective muscarinic DREADD agonists and so can activate or inhibit neuronal activity, depending on the specific receptor being expressed. Salvinorin B is selective for the KORD receptor, which is coupled to GαI signaling; consequently binding results in inhibition of neuronal activity.


www.tocris.com | 13

Box 5: Chemogenetic compounds

Cl

NH

N

N+CH3

O-

N2HCl

Clozapine N-oxide dihydrochloride (6329)Activator of muscarinic DREADDs; water soluble

version of Clozapine N-oxide (Cat. No. 4936)

N

NH

N

NH

2HCl

DREADD agonist 21 dihydrochloride (6422)Potent muscarinic DREADD agonist; water soluble

version of DREADD agonist 21 (Cat. No. 5548)

N

N

N

Perlapine (5549)Potent muscarinic DREADD agonist

O

O

O

O

(E)

(Z)

HH

Me

Me

HO

OMeO

Salvinorin B (5611)Activates the κ-opioid DREADD (KORD)

N NN

PSEM 308 (6425)PSAML141F-GlyR and PSAML141F,Y115F-5-HT3

chimeric ion channel agonist

OMe

O

HN

N

MeO

PSEM 89S (6426)PSAML141F-GlyR and PSAML141F,Y115F-5-HT3

chimeric ion channel agonist

Box 5: Chemogenetics Compounds: DREADD Ligands and PSEMsSee pages 23-33 for a full list of targets and related products

Chemogenetics Research Bulletin

Produced by Tocris, the chemogenetics research bulletin provides an introduction to chemogenetic methods to manipulate neuronal activity. It outlines the development of RASSLs, DREADDs and PSAMs, and the use of chemogenetic compounds. DREADD ligands and PSEMs available from Tocris are highlighted.

Text excerpt: “All DREADDs have some common features that make them ideal for use in neuroscience experiments. Firstly, DREADDs exhibit no response to endogenous ligands due to genetic mutations within their ligand binding sites that abolish binding. This means that any activity of the DREADD will be solely due to the specific DREADD ligand applied. Secondly, expression of DREADDs in vitro or in vivo, has no effect on cellular activity, neuronal function or baseline behaviors, prior to the addition of the DREADD ligand (Sternson & Roth, 2014).”


14 |

Depression ResearchMajor depressive disorder (MDD) is an affective disorder char-acterized by the core symptoms of depressed mood and loss of interest and/or pleasure, often accompanied by sleep distur-bances, fatigue and altered ability to concentrate. The pervad-ing biochemical theory to explain the neurobiological causes of MDD is the monoamine hypothesis, which suggests that an imbalance in monoamine (5-HT, DA and NE) signaling is to blame. This theory grew from the observation that various drugs known to alter monoamine neurotransmission mimic or alleviate the symptoms of depression. For example, the VMAT2 inhibitor reserpine (Tocris, Cat. No. 2742), originally intro-duced as an antihypertensive drug, has an inhibitory effect on monoamine transmission and is associated with a lowering of mood. Also, MAO inhibitors that block the breakdown of monoamines and were originally introduced to treat tubercu-losis, are associated with a marked elevation in mood. Selective 5-HT reuptake inhibitors (SSRIs) are currently the most pre-scribed antidepressant, although compounds including non-competitive NMDAR antagonists, anticholinergic agents and opioid signaling modulators are under investigation as potential therapies.

Currently available animal models and tests to investigate MDD neurobiology and identify new treatments are limited, as subjective measures used to study mood disorders in humans


5-HT Transporters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235-HT1 Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235-HT2 Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235-HT3-7 Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Acetylcholine Transporters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25Adrenergic α-receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25Adrenergic β-receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25Adrenergic Transporters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25AMPA Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25Dopamine D1-like Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27Dopamine D2-like Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Dopamine Transporters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28Glutamate Transporters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29Kainate Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30κ Opioid Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Metabotropic Glutamate Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30Monoamine Oxidases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31NMDA Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32Vesicular Monoamine Transporters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Figure 12 | Positive Affective Bias Induced by Antidepressants

Dose (mg/kg)

0.0

15

10

5

0

-50.3 1.0 3.0

% C

hoic

e bi

asflu

oxet

ine-

paire

d su

bstr

ate

***

*****

Dose (mg/kg)

0.0

15

10

5

0

-51.0 3.0 10.0

% C

hoic

e bi

asve

nlaf

axin

e-pa

ired

subs

trat

e

**

*** ***

Dose (mg/kg)

0.0

15

10

5

0

-50.1 0.3 1.0

% C

hoic

e bi

asag

omel

atin

e-pa

ired

subs

trat

e

**

**

Dose (mg/kg)

0.0 0.0

15

10

5

0

-51.0 3.0 10.00.3 10.0 30.0

% C

hoic

e bi

asap

repi

tant

-pai

red

subs

trat

e

Dose (mg/kg)

0.0

15

10

5

0

-50.1 0.3 1.0

% C

hoic

e bi

asre

boxe

tine-

paire

d su

bstr

ate

***

Dose (mg/kg)

0.0

15

10

5

0

-50.1 0.3 1.0 3.0

% C

hoic

e bi

asci

talo

pram

-pai

red

subs

trat

e

A B C

D E F

Fluoxetine (A), citalopram (B), reboxetine (C), venlafaxine (D) and agomelatine (E) induce a significant positive affective bias in the ABT in rats. The neurokinin 1 receptor antagonist aprepitant (F) failed to cause a significant change in affective bias. * p<0.05, ** p<0.01, *** p<0.005. Adapted from Stuart et al, 2013.


www.tocris.com | 15

cannot be replicated in animals, i.e. you can’t ask a rodent how it ‘feels’. Recent advances in cognitive neuropsychological testing in humans have provided an opportunity to translate these tests to develop methods of the assessment of depressive behaviors in rodents.

Acute and long-term antidepressant treatments induce a posi-tive shift in emotional processing, also known as cognitive affective bias, in humans (Pringle etal, 2011). In their paper, Stuart etal describe the evaluation of an affective bias test (ABT) for rats, using a range of compounds with acute effects on affective bias in humans (Stuart etal, 2013). In the ABT, rats encounter two independent positive experiences (the association of food reward with a specific digging material) in learning sessions. Affective bias is then quantified using a pref-erence test, in which both previously rewarded digging mat-erials are presented together and the rat’s choice in recorded.

Using ABT, they showed the SSRIs fluoxetine (Tocris, Cat. No 0927), citalopram (Tocris, Cat. No. 1427) and clomipramine (Tocris, Cat. No. 0457); the selective NE reuptake inhibi-tor reboxetine (Tocris, Cat. No. 1982); the mixed 5-HT/NE reuptake inhibitor venlafaxine (Tocris, Cat. No. 2917); and the 5-HT2 antagonist mirtazapine (Tocris, Cat. No. 2018) induced a significant positive affective bias, replicating results seen in humans (Figure 12). They also showed induction of a negative affective bias by compounds associated with negative bias in humans, including the cannabinoid CB1 receptor inverse ago-nist rimonabant (Tocris, SR 141716A, Cat. No. 0923) and the benzodiazepine inverse agonist FG7142 (Tocris, Cat. No. 0554). Acute psychosocial stress and environmental enrich-ment also induced significant negative and positive affective bias, respectively (Stuart etal, 2013).

Box 6: Antidepressants

O

Me2NF

NC

Citalopram (1427)Highly potent and selective 5-HT uptake inhibitor

NHMe

Cl

Cl

Sertraline (2395)5-HT re-uptake inhibitor

MeO

Me2N

OH

Venlafaxine (2917)Dual 5-HT/noradrenalin re-uptake inhibitor

NN

N

Me

Mirtazapine (2018)Potent 5-HT2 antagonist; also 5-HT3,

H1 and α2 antagonist

N

NMe2

Cl

Clomipramine (0457)5-HT re-uptake inhibitor

O

O

NH

H

O

Reboxetine (1982)Potent and selective noradrenalin

uptake inhibitor; orally active

Box 6: AntidepressantsSee pages 23-33 for a full list of targets and related products


16 |

Depression – continued

Modulators of opioid signaling are currently under investiga-tion for their efficacy as antidepressants. The expression of KOR is increased in Wistar-Kyoto (WKY) rats (Pearson etal, 2006), a strain originally developed as a normotensive control for the spontaneously hypertensive rat strain, which is known to have increased sensitivity towards stress (Pare, 1992; 1994). KOR agonists cause depressive behaviors in commonly used rodent models (McLaughlin etal, 2006a), while KOR antagonists pro-duce an antidepressant-like effect (McLaughlin etal, 2006b).

In their paper, Carr etal confirmed the antidepressant-like effects of the selective KOR antagonists Nor-Binaltorphimine

Nor-BNI (A) and DIPPA (B and C) significantly reduced immobility and increased swimming behavior in WKY rats, but not SD rats. # indicates a significant difference between saline-treated groups across the two strains, # p<0.001. Asterisks indicate a significant difference within each strain, compared to the saline-treated group, * p<0.05, ** p<0.01. Adapted from Carr et al, 2010.

* *

*

* *

* *

#

#

**

Sprague DawleyA

B C

Wistar Kyoto

Sprague Dawley Wistar Kyoto

Swimming SwimmingClimbing ClimbingImmobilityImmobility

Cou

nt

5

10

15

20

25

30

35

40

45

50

0

Immobility Swimming Climbing

Cou

nt

5

10

15

20

25

30

35

40

45

50

0

**

Immobility Swimming Climbing

Cou

nt

5

10

15

20

25

30

35

40

45

50

0

Saline

nor-BNI (1 mg/kg)nor-BNI (5 mg/kg)nor-BNI (10 mg/kg)

Saline

DIPPA (5 mg/kg)DIPPA (10 mg/kg)

Saline

DIPPA (1 mg/kg)DIPPA (2.5 mg/kg)

DIPPA (5 mg/kg)

DIPPA (10 mg/kg)

Figure 13 | Antidepressant-like Effects of KOR Antagonists in the Forced Swim Test

(nor-BNI, Tocris, Cat. No. 0347) and DIPPA (Tocris, Cat. No. 0794), in WKY rats when compared to the Sprague-Dawley (SD) rat strain, using the forced swim test (Figure 13). C-fos expression, a marker of neuronal activity, was altered in the piriform cortex and nucleus accumbens following KOR antago-nist treatment. Also, direct administration of nor-BNI into the piriform cortex induced antidepressant-like effects implicating this area in the antidepressant-like activity of KOR antagonists (Carr etal, 2010).


www.tocris.com | 17

Box 7: Ketamine and its Metabolites

OCl

NHMe

Ketamine (3131)Non-competitive NMDA antagonist

Cl

NH2

O

Norketamine (1970)Potent non-competitive NMDA antagonist;

antinociceptive

Cl

NH2O

HO

2R,6R-Hydroxynorketamine (6094)Enhances AMPA currents; decreases D-serine (NMDA co-agonist);

lacks ketamine-related side effects

(and enantiomer)Cl

NH2O

HO

cis-6-Hydroxynorketamine (5982)Enhances AMPA currents; antidepressant

Box 7: Ketamine and its MetabolitesSee pages 23-33 for a full list of targets and related products

Ketamine Metabolites for the Treatment of Depression

Ketamine (Tocris, Cat. No. 3131) is a non-competitive NMDA receptor antagonist that demonstrates a rapid and robust anti-depressant effect in patients, occurring within a few hours of administration and with long-lasting effects. This gives keta-mine advantages over current antidepressants, which generally have a long lead time before showing their beneficial effects and have a high non-response rate. However, the use of ketamine is hampered by its liability for abuse and dissociative side effects even at low doses.

Recent investigations have indicated that metabolites of keta-mine may be responsible for its antidepressant effects. Invivo, ketamine is converted to metabolites including norketamine (Tocris, Cat. No. 1970), hydroxyketamines, dehydroxynorketa-mines and hydroxynorketamines. (R)- and (S)-Norketamine (Tocris, Cat. Nos. 5996 and 6112, respectively) both modulate NMDA receptor activity and act as analgesics in rat models of

neuropathic pain. Also, 2R,6R-Hydroxynorketamine (Tocris, Cat. No. 6094) and 2S,6S-Hydroxynorketamine (Tocris, Cat. No. 6095) both reduce intracellular D-serine concentrations required for NMDA receptor opening, displaying more potent inhibition than other ketamine metabolites.

2R,6R-Hydroxynorketamine displays rapid and persistent antidepressant effects in various animal models of depression. Unlike other metabolites, it does not displace the noncompeti-tive NMDA antagonist MK-801 (Tocris, Cat. No. 0924) from its binding site in the NMDA ion channel suggesting another specific site of action. It causes increases in AMPA receptor mediated excitatory postsynaptic potentials (EPSPs), causing an increase in glutamatergic signaling with subsequent upregu-lation of synaptic AMPA receptors. Additionally, even at high doses 2R,6R-Hydroxynorketamine shows none of the addictive and dissociative side effects of ketamine.


18 |

Addiction Research

Drug addiction refers to the processes by which people become dependent on the use of drugs, alcohol or even gambling, to the point where it interferes with and eventually takes over their life. Not all those who take drugs become addicted; there are several factors that predispose to addiction, including class of drug, family history of addiction and propensity for with-drawal reaction and cravings. There are three defining features of addiction: compulsion to take the drug, loss of control of limiting intake and withdrawal symptoms when the drug is withheld.

Using preclinical and human imaging, the brain circuits involved in addiction have been characterized. There are four interacting circuits that are involved to varying extents, depending on the addictive substance. The reward circuit is a dopaminergic pathway from the ventral tegmental area (VTA) to the nucleus accumbens (NAcc). The hippocampus and amyg-dala regulate the encoding and reactivation of memories asso-ciated with drug use, with the hippocampus being responsible for place memories and the amygdala being responsible for the emotional aspect of memories. A separate pathway, involving areas of the prefrontal cortex and anterior cingulate cortex, is responsible for cognitive control and relies on the balance of glutamatergic and GABAergic signaling to exert ‘top-down’ control of the motivation and pleasure areas (Figure 14).

As outlined above, the rewarding aspects of drug addiction originate in a dopaminergic circuit. Cocaine (Tocris, Cat. No. 2833) is a competitive inhibitor of DAT and so blocks the reuptake of DA and increases dopaminergic transmission.

This underlies the reward/reinforcement aspect of cocaine use, leading to drug abuse and addiction (Rice & Cragg, 2008). Invitroinvestigations have suggested that cocaine may have allosteric actions at D2R, known to play a role in the abuse related side effects of cocaine. At low concentrations, known not to inhibit DAT, cocaine enhances the ability of quinpirole, a selective D2-like receptor agonist (Tocris, Cat. No. 1061), to reduce labeled DA efflux from synaptosomes, evoked by K+ (Ferraro et al, 2010b). This was further investigated invivo, demonstrating that when given in combination with quin-pirole, cocaine significantly increased quinpirole-induced hyperlocomotion in rats (Figure 15). Cocaine also enhanced the Gi/o coupling of D2Rs, possibly by either an allosteric direct or indirect enhancing effect (Ferraro etal, 2010a). These results suggest a novel mechanism for cocaine, with relevance for understanding the rewarding aspect of cocaine addiction.

Extinction of drug addiction promotes abstinence from drug seeking behaviors. This is an active learning process involving inhibition of learned motivations and behaviors, and is depend-ent on the infralimbic prefrontal cortex (ilPFC). As well as its established role in feeding as a motivated behavior, the hypo-thalamus is also thought to play a role in reinstatement of drug addiction and associated reward seeking behaviors. Various lines of evidence suggest a commonality between the circuits responsible for reinstatement of drug seeking behaviors and


5-HT Transporters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235-HT1 Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235-HT2 Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235-HT3-7 Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Acetylcholine Nicotinic Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24AMPA Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25Cannabinoid CB1 Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26Cannabinoid CB2 Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26Dopamine D1-like Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27Dopamine D2-like Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28Dopamine Transporters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28δ Opioid Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 GABAA Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28GABAA-ρ Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29Glutamate Transporters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Kainate Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30κ Opioid Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30µ Opioid Receptors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31NMDA Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Figure 14 | Brain Circuits Associated with Addiction

Four interacting circuits are invovled in addiction, modulating reward prediction and pleasure (green), memory (red), motivation (blue) and cognition (purple) to varying extents depending on the individual and the addictive substance in question. Use of addictive substances leads to adaptive changes, for example in the ‘top-down’ control over urges and impulses provided by the function of the PFC/OFC connection. AGC – Anterior cingulate gyrus; Amyg – Amygdala, HIP – Hippocampus, NAcc – Nucleus accumbers, OFC – orbitao-frontal cortex, PFC – Prefrontal cortex, VP – Ventral palladium. Adapted from Baler & Volkow, 2006.

PFC

ACG

OFCHIP

Amyg

NAccVP


www.tocris.com | 19

8000

Dis

tanc

e tr

avel

ed (

cm γ

120

min

)

6000

4000

2000

VehVeh

Coc 0.625Veh

Coc 0.625Quin 0.5

Coc 0.625Quin 1

VehQuin 0.5

VehQuin 1

0

**

**

*

*

<

Cocaine (0.625 mg/kg) significantly enhances quinpirole (0.5 or 1 mg/kg) -induced hyperlocomotion, in a concentration dependent manner, but has no effect on locomotion when given alone. Coc – cocaine, Quin – quinpirole, Veh – vehicle. * p<0.05, ** p<0.01 vs Veh+Veh group. ^ p<0.05 vs Veh+Quin 1 group. Adapted from Ferraro et al, 2010.

Figure 15 | Effect of Cocaine on Drug-Induced Locomotion

Box 8: Addiction

NCO2Me

O

O

H

H

Cocaine (2833)Inhibitor of monoamine transporters

NH2

D-Amphetamine (2813)Induces dopamine, 5-HTand noradrenalin release

O

O NHMe

(±)-MDMA (3027)Inhibitor of 5-HT and dopamine uptake;

hallucinogenic

OH

Me

Me

MeOH

(-)-Cannabidiol (1570)Natural cannabinoid; GPR55 antagonist, weak CB1antagonist, CB2 inverse agonist and AMT inhibitor

N

Phencyclidine (2557)Non-competitive NMDA antagonist

N

N

(-)-Nicotine (3546)Prototypical nAChR agonist

N

OHHO O

H

Morphine (5158)Narcotic opioid analgesic

Box 8: AddictionSee pages 23-33 for a full list of targets and related products

those controlling feeding. Using complementary functional and neuroanatomical techniques, Marchant etal investigated the role of the medial dorsal hypothalamus (MDH) in the extinc-tion of alcohol seeking behavior in rats. Neurons projecting from ilPCF to MDH are known to be necessary for extinction invivo, and MDH neurons projecting to the paraventricular nucleus of the thalamus (PVN) are also thought to be involved. MDH to PVN neurons showed expression of dynorphins, and infusion of the KOR agonist (±)-U-50488 (Tocris, Cat. No. 0495) into the PVN prevented reinstatement of alcohol-seeking behavior. This indicates that PVN KOR activation can inhibit alcohol-seeking behaviors in rats, affecting a neuronal circuit involving MDH and ilPCF (Marchant etal, 2010).


20 |

Epilepsy is a common neurological disorder, frequently result-ing from traumatic brain injury and acquired pathology including tumors or infection. Epileptic seizures arise from abnormal, excessive or synchronous neuronal activity, resulting in sensory disturbances, loss of consciousness and/or convul-sions. Epilepsy can also be caused by mutations in a single gene, however in most cases the exact cause is unknown.

Seizures arise when there is a disruption in the balance of exci-tation and inhibition within neuronal circuits. The activity of a network of neurons, rather than of a single neuron, must be altered to cause a seizure. Many mechanisms that occur during epileptogenesis promote cell activity synchronization, through changes to neurotransmission in glutamatergic interneurons and GABAergic connections.

The most common form of epilepsy is temporal lobe epilepsy (TLE), which is associated with cognitive changes. Changes in the expression of various ion channels and neurotransmitter

receptors have been identified in TLE, while at a cellular level inflammation, neuronal cell death and reactive astrocytosis are seen.

NMDARs mediate synaptic plasticity, a process essential to most forms of learning and memory. Full activation of NMDARs requires binding of D-serine or glycine as an allos-teric co-agonist. D-serine, which binds at a separate binding site to glutamate, is released from astrocytes in a Ca2+-dependent manner, regulating activation of NMDARs and therefore synaptic plasticity.

In their investigation, Klatte etal showed that D-serine levels are reduced in a rat model of TLE, induced by treatment with the muscarinic agonist pilocarpine (Tocris, Cat. No. 0694). This resulted in desaturation of synaptic and extrasynaptic NMDARs and deficits in hippocampal long-term potentiation (LTP), the strengthening of the connection between neurons that is thought to underlie learning and memory. Exogenous application of D-serine (Tocris, Cat. No. 0226) rescues hippo-campal LTP in the pilocarpine TLE model, which is reversed by the potent D-serine/glycine site antagonist CGP78606 (Tocris, Cat. No. 1493). TLE induction impairs working mem-ory in rats, as shown by an increase in distance travelled in the Morris water maze. D-serine treatment ameliorated these behavioral deficits (Klatte etal, 2013) (Figure 16). These results suggest that D-serine has a beneficial effect on cognitive changes seen in TLE.

Epilepsy Research


AMPA Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25GABAA Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28GABAA-ρ Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29Kainate Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30Metabotropic Glutamate Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30NMDA Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Box 9: Epilepsy

N

NH2O

Carbamazepine (4098)Inhibitor of neuronal NaV channels;

anticonvulsant

CO2Na

Valproic acid (2815)Increases GABA levels;

anticonvulsant

NN

N NH2H2N

Cl

Cl

Lamotrigine (1611)Inhibits glutamate release;

anticonvulsant

NH2CO2H

Gabapentin (0806)Increases brain GABA;

anticonvulsant

OH

H

HO2CCO2H

H2N

LY 379268 (2453)Highly selective group II mGlu agonist

NMe

MPEP (1212)Potent mGlu5 antagonist; positive

allosteric modulator at mGlu4

NC

N

N

O2N

O-

O-

.2Na+

CNQX disodium salt (1045)Potent non-NMDA iGluR antagonist; water soluble

version of CNQX (Cat. No. 0190)

Box 9: EpilepsyA full list of targets and related products are listed on pages 23-33


www.tocris.com | 21

A) Following TLE induction, D-serine levels are significantly decreased in the cortex and hippocampus, determined by high performance liquid chromatography (HPLC). B) Induction of TLE significantly impairs LTP in the hippocampus, which is reversed by exogenous application of D-serine. The action of D-serine is blocked by addition of CGP 78608. C) TLE induction impairs working memory, shown by increased distance travelled in the Morris water maze on consecutive trials on the first day of training. D-serine had no significant effect on working memory. D) On the first trial of consecutive days of testing, TLE induction increased the distanced travelled to reach the platform, showing a cognitive deficit that was significantly improved by D-serine. n.s. – not significant, * p<0.05, ** p<0.01, *** p<0.005. Adapted from Klatte et al, 2013.

Figure 16 | Assessment of D-serine and LTP in a Pilocarpine Induced TLE Model

400

n. s.(10) (10)

(14)

(14)

(12)

(13)350

300

200

150

50

0

200

150

50

0Cortex

% D

-ser

ine

cont

ent

Hippocampus

HPLC

BA

C

Native D-ser D-ser+ CGP

**

** **

fEP

SP s

lope

(%

bas

elin

e)

1800

1400

1000

600

200

1600

1200

800

400

01 2 3 4 5 6

D

Trial (first day)

Dis

tanc

e (c

m)

**

****

*

ShamPost-SE

ShamSham, D-serinePost-SEPost-SE, D-serine

1800

1400

1000

600

200

1600

1200

800

400

01 2 3 4 5 6 7

Day

Dis

tanc

e (c

m)


22 |

List of Acronyms

Acronym Definition Acronym Definition

5-HT Serotonin

cAMP Cyclic adenosine monophosphate

COMT Catechol O-Methyltransferase

DA Dopamine

DAG Diacylglycerol

DAT Dopamine transporter

DDC Dopa decarboxylase

DOR δ-opioid receptor

DREADDs Designer Receptors Activated by Designer Drugs

EAAT Excitatory amino acid transporters

EPSP Excitatory postsynaptic potential

GPCRs G protein-coupled receptors

ilPFC Infralimbic prefrontal cortex

IP3 Inositol 1,4,5-trisphosphate

KOR κ-opioid receptor

LGIC Ligand gated ion channel

LTP Long term potentiation

MAO Monoamine oxidase

MDD Major depressive disorder

MDH Medial dorsal hypothalamus

mGluR Metabotropic glutamate receptors

MOR µ-opioid receptor

NAcc Nucleus accumbens

NMDARs NMDA receptors

NE Norepinephrine

NOP Nociceptin/orphanin FQ receptor

PLC Phospholipase C

PSAM Pharmacologically Selective Actuator Module

PSEM Pharmacologically Selective Effector Molecule

PVN Paraventricular nucleus of the hypothalamus

SERT Serotonin transporter

SSRI Selective serotonin reuptake inhibitor

TH Tyrosine hydroxylase

TLE Temporal lobe epilepsy

TPH Tryptophan hydroxylase

VGLUT Vesicular glutamate transporter

VMATs Vesicular monoamine transporter

VTA Ventral tegmental area


www.tocris.com | 23

Neurotransmission Research Products

Class Cat. No. Product Name Primary Action Unit Size

5-HT Transporters

Inhibitors 1427 Citalopram Highly potent and selective 5-HT uptake inhibitor 10 mg50 mg

4798 (S)-Duloxetine Potent 5-HT and NA reuptake inhibitor; also blocks dopamine reuptake 10 mg50 mg

4796 Escitalopram Selective serotonin reuptake inhibitor (SSRI) 10 mg50 mg

0927 Fluoxetine 5-HT reuptake inhibitor 10 mg50 mg

5-HT1 Receptors

Agonists 1080 (R)-(+)-8-Hydroxy-DPAT Selective 5-HT1A agonist; enantiomer of 8-Hydroxy-DPAT hydrobromide (Cat. No. 0529)

10 mg50 mg

0529 8-Hydroxy-DPAT Selective 5-HT1A agonist; also has moderate affinity for 5-HT7 10 mg50 mg

1317 CP 94253 Potent and selective 5-HT1B agonist 10 mg50 mg

2451 LY 344864 Potent and selective 5-HT1F agonist 10 mg50 mg

2854 Tandospirone Selective 5-HT1A partial agonist 10 mg50 mg

Antagonists 1477 GR 127935 Potent and selective 5-HT1B/1D antagonist 10 mg50 mg

1221 SB 224289 Selective 5-HT1B antagonist 10 mg50 mg

1253 (S)-WAY 100135 Potent and selective 5-HT1A antagonist 10 mg50 mg

4380 WAY 100635 Potent 5-HT1A antagonist; also D4 agonist 10 mg50 mg

5-HT2 Receptors

Agonists 5171 NBOH-2C-CN High affinity and selective 5-HT2A agonist 10 mg50 mg

2592 TCB-2 High affinity and potent 5-HT2A agonist 10 mg50 mg

1801 WAY 161503 Potent and selective 5-HT2C agonist 10 mg50 mg

Antagonists 4081 LY 266097 Selective 5-HT2B antagonist 10 mg50 mg

4173 MDL 100907 Potent and selective 5-HT2A antagonist 10 mg50 mg

1955 Ritanserin Potent 5-HT2 antagonist 10 mg50 mg

2993 RS 127445 High affinity and selective 5-HT2B antagonist 10 mg50 mg

2901 SB 242084 Selective 5-HT2C antagonist; brain penetrant 10 mg50 mg

5-HT3-7 Receptors

Agonists 1968 AS 19 Potent 5-HT7 agonist 10 mg50 mg

4374 BIMU 8 Potent 5-HT4 agonist 5 mg25 mg

1205 SR 57227 Potent and selective 5-HT3 agonist 10 mg50 mg

5589 WAY 181187 High affinity and selective 5-HT6 agonist 10 mg50 mg


24 |

Antagonists 1658 GR 125487 Potent and selective 5-HT4 antagonist; active in vivo 10 mg50 mg

2891 Ondansetron Selective 5-HT3 antagonist 10 mg50 mg

1612 SB 269970 Potent and selective 5-HT7 antagonist; brain penetrant 10 mg50 mg

3189 SB 399885 Potent and selective 5-HT6 antagonist 10 mg50 mg

Acetylcholine Muscarinic Receptors

Agonist 3569 Xanomeline Functionally selective M1 agonist 10 mg50 mg

Antagonists 2292 AQ-RA 741 High affinity and selective M2 antagonist 10 mg50 mg

2507 J 104129 Potent and selective M3 antagonist 10 mg

1071 Pirenzepine Selective M1 antagonist 100 mg

0909 Tropicamide Selective M4 antagonist 100 mg

3727 VU 0255035 Highly selective M1 antagonist 5 mg25 mg

Modulators 3634 VU 0238429 Selective positive allosteric modulator of M5 receptors 10 mg50 mg

4295 VU 0357017 Positive allosteric modulator of M1 receptors 10 mg50 mg

3383 VU 152100 Positive allosteric modulator of M4 receptors 10 mg50 mg

Acetylcholine Nicotinic Receptors

Agonists 0684 (±)-Epibatidine High affinity nAChR agonist 10 mg

3546 (-)-Nicotine Prototypical nAChR agonist 50 mg

6140 NS 6784 α7 nAChR agonist 10 mg50 mg

3092 PHA 543613 Potent and selective α7 nAChR agonist 10 mg

5559 SSR 180711 Selective α7 nAChR partial agonist 10 mg50 mg

3754 Varenicline Selective α4β2 nAChR partial agonist; orally active 10 mg50 mg

Antagonists 2133 α-Bungarotoxin Selective α7 nAChR antagonist 1 mg

1340 α-Conotoxin MII Potent and selective α3β2 and β3 nAChR antagonist 500 µg

3123 α-Conotoxin PnIA Selective α3β2 nAChR antagonist 500 µg

2349 Dihydro-β-erythroidine α4β2, muscle type and Torpedo nAChR antagonist 10 mg50 mg

2843 Mecamylamine Non-competitive nAChR antagonist 10 mg50 mg

1029 Methyllycaconitine Selective α7 neuronal nAChR antagonist 5 mg25 mg

Modulators 5963 CMPI Potent positive allosteric modulator of α4β2 nAChRs; also inhibitor of (α4)2(β2)3, muscle-type and Torpedo nAChRs

10 mg

5112 NS 9283 Positive allosteric modulator of α4β2 nAChRs 10 mg50 mg

2498 PNU 120596 Positive allosteric modulator of α7 nAChRs; active in vivo 5 mg25 mg

Other 2736 Sazetidine A α4β2 nAChR ligand; may act as an agonist or a desensitizer 10 mg

Acetylcholine Receptors: Non-selective Compounds

Agonists 2810 Carbamoylcholine Non-selective cholinergic agonist 100 mg



www.tocris.com | 25

Neurotransmission Research Products – continued

Acetylcholine Transporters

Inhibitors 0653 (±)-Vesamicol Inhibits ACh transport 250 mg

Others 5725 ML 352 High affinity and selective presynaptic choline transporter (CHT) inhibitor 10 mg50 mg

Adenylyl Cyclase

Activators 1099 Forskolin Adenylyl cyclase activator 10 mg50 mg

Inhibitors 3834 KH 7 Selective soluble adenylyl cyclase inhibitor 10 mg50 mg

1435 SQ 22536 Adenylyl cyclase inhibitor 10 mg50 mg

Adrenergic α Receptors

Agonists 1052 A 61603 α1A agonist 10 mg50 mg

5160 Medetomidine Potent and highly selective α2 agonist 10 mg50 mg

Antagonists 2937 Atipamezole Selective α2 antagonist 10 mg50 mg

2964 Doxazosin α1 antagonist 50 mg

0623 Prazosin α1 and α2B antagonist; also melatonin MT3 antagonist 100 mg

0987 RS 79948 Potent and selective α2 antagonist 10 mg50 mg

Adrenergic β Receptors

Agonists 1499 CL 316243 Highly selective β3 agonist 10 mg50 mg

1448 Formoterol Potent and selective β2 agonist 10 mg50 mg

1747 Isoproterenol Standard selective β agonist 100 mg

0950 Xamoterol Selective β1 partial agonist 10 mg50 mg

Antagonists 2685 Carvedilol Potent and non-selective β antagonist; also α1 antagonist 50 mg

1024 CGP 20712 Highly potent and selective β1 antagonist 10 mg50 mg

1511 SR 59230A Potent and selective β3 antagonist 10 mg50 mg

Inverse Agonists 0821 ICI 118,551 Highly selective β2 inverse agonist 10 mg50 mg

Adrenergic Transporters

Inhibitors 3067 Desipramine Selective inhibitor of noradrenalin transporters 50 mg

1982 Reboxetine Potent and selective noradrenalin uptake inhibitor; orally active 10 mg50 mg

2011 Tomoxetine Potent and selective noradrenalin re-uptake inhibitor 10 mg50 mg

AMPA Receptors

Agonists 0254 (S)-AMPA Selective AMPA agonist; active isomer of (RS)-AMPA (Cat. No. 0169) 1 mg10 mg50 mg

Antagonists 2312 DNQX disodium salt Selective non-NMDA iGluR antagonist; water-soluble salt of DNQX (Cat. No. 0189)

10 mg50 mg

2555 GYKI 53655 Non-competitive AMPA antagonist; also kainate antagonist 10 mg50 mg

2766 Naspm Ca2+-permeable AMPA antagonist 10 mg

1044 NBQX disodium salt Potent AMPA antagonist; more water-soluble form of NBQX (Cat. No. 0373) 1 mg10 mg50 mg



26 |

Modulators 2980 CX 546 AMPA potentiator 10 mg50 mg

0713 Cyclothiazide Positive allosteric modulator of AMPA receptors; inhibits AMPA desensitization

10 mg50 mg

6278 JNJ 55511118 High affinity and selective negative modulator of AMPA receptors containing TARP-γ8

5 mg25 mg

Caged Compounds

5785 MDNI-caged-L-glutamate Stable photoreleaser of l-glutamate 10 mg

1490 MNI-caged-L-glutamate Stable photoreleaser of l-glutamate 10 mg50 mg

2224 MNI-caged-NMDA Caged NMDA 10 mg

3991 NPEC-caged-serotonin Caged serotonin 10 mg50 mg

4932 RuBi-Dopa Caged dopamine; exhibits two-photon sensitivity 10 mg

3400 RuBi-GABA Caged GABA; excitable at visible wavelengths 10 mg

cAMP

Antagonists 1337 cAMPS-Rp cAMP antagonist 1 mg

Others 5255 6-Bnz-cAMP Cell-permeable cAMP analog 1 mg

1140 8-Bromo-cAMP Cell-permeable cAMP analog 10 mg50 mg

1141 Dibutyryl-cAMP Cell-permeable cAMP analog 10 mg50 mg

Cannabinoid CB1 Receptors

Agonists 1319 ACEA Potent and highly selective CB1 agonist 5 mg25 mg

1782 (R)-(+)-Methanandamide (in Tocrisolve™ 100)

Potent and selective CB1 agonist; supplied in water-soluble emulsion 5 mg25 mg

Antagonists 1117 AM 251 Potent CB1 antagonist; also GPR55 agonist 1 mg10 mg50 mg

5443 AM 6545 High affinity and selective CB1 antagonist 10 mg50 mg

Inverse Agonists 1115 AM 281 Potent and selective CB1 inverse agonist 10 mg50 mg

0923 SR 141716A Selective CB1 inverse agonist 10 mg50 mg

Modulators 2957 Org 27569 Potent allosteric modulator of CB1 receptors 10 mg50 mg

5321 PSNCBAM-1 Negative allosteric modulator of CB1 receptors 10 mg50 mg

Cannabinoid CB2 Receptors

Agonists 3088 HU 308 Potent and selective CB2 agonist 10 mg50 mg

1343 JWH 133 Potent and selective CB2 agonist 10 mg

Inverse Agonists 1120 AM 630 Selective CB2 inverse agonist 10 mg50 mg

5039 SR 144528 High affinity and selective CB2 inverse agonist 10 mg50 mg



www.tocris.com | 27


Cannabinoid Receptors: Non-selective Compounds

Agonists 1298 2-Arachidonylglycerol Endogenous and non-selective CB agonist; potent GPR55 agonist 10 mg

1339 Anandamide Endogenous and non-selective CB agonist 5 mg25 mg

0949 CP 55,940 Potent and non-selective CB agonist 10 mg50 mg

1038 WIN 55,212-2 Highly potent and non-selective CB agonist 10 mg50 mg

Cannabinoid Transporters

Inhibitors 1116 AM 404 Anandamide transport inhibitor 10 mg50 mg

1570 (-)-Cannabidiol AMT inhibitor; also GPR55 antagonist, weak CB1 antagonist, CB2 inverse agonist; natural cannabinoid

10 mg50 mg

Catechol O-Methyltransferase

Inhibitors 0483 OR-486 COMT inhibitor 50 mg

5864 Tolcapone COMT inhibitor; also inhibits transthyretin aggregation 10 mg50 mg

Chemogenetics

DREADD Ligands 4936 Clozapine N-oxide Activator of muscarinic DREADDs 10 mg50 mg

6329 Clozapine N-oxide dihydrochloride

Activator of muscarinic DREADDs; water-soluble version of Clozapine N-oxide (Cat. No. 4936)

10 mg50 mg

5548 DREADD agonist 21 Potent muscarinic DREADD agonist 10 mg50 mg

6422 DREADD agonist 21 dihydrochloride

Potent muscarinic DREADD agonist; water-soluble version of DREADD agonist 21 (Cat. No. 5548)

10 mg50 mg

5549 Perlapine Potent muscarinc DREADD agonist 10 mg50 mg

5611 Salvinorin B Activates the κ-opioid DREADD (KORD) 1 mg

PSEMs 6425 PSEM 308 PSAML141F-GlyR and PSAML141F,Y115F-5-HT3 chimeric ion channel agonist 5 mg25 mg

6426 PSEM 89S PSAML141F-GlyR and PSAML141F,Y115F-5-HT3 chimeric ion channel agonist 5 mg25 mg

Cholinesterases

Inhibitors 4385 Donepezil Potent AChE inhibitor 10 mg50 mg

0622 Physostigmine Cholinesterase inhibitor 10 mg

Decarboxylases

Inhibitors 0455 (S)-(-)-Carbidopa Aromatic L-amino acid decarboxylase inhibitor 25 mg

0584 L-(-)-α-Methyldopa Aromatic L-amino acid decarboxylase inhibitor 1 g

Dopamine D1-like Receptors

Agonists 1701 A 77636 Potent and selective D1-like agonist; orally active 10 mg50 mg

0884 Dihydrexidine Selective D1-like agonist 5 mg25 mg

1447 SKF 81297 D1 agonist 10 mg50 mg

5719 SKF 82958 D1 agonist 10 mg50 mg

Antagonists 1674 LE 300 Potent and selective D1 antagonist 10 mg

2299 SCH 39166 High affinity D1-like antagonist 10 mg50 mg



28 |

Dopamine D2-like Receptors

Agonists 4552 A 412997 Selective D4 agonist 5 mg25 mg

1243 (+)-PD 128907 High affinity D3 agonist (D3 ≥ D2 > D4) 10 mg50 mg

1061 (-)-Quinpirole Selective D2-like agonist 10 mg50 mg

2773 Sumanirole Selective D2 agonist 10 mg50 mg

Antagonists 1003 L-741,626 High affinity D2 antagonist 10 mg50 mg

1002 L-745,870 Highly selective D4 antagonist 10 mg50 mg

4207 SB 277011A Selective D3 antagonist 10 mg50 mg

Dopamine Receptors: Non-selective Compounds

Antagonists 0444 Clozapine Dopamine antagonist with some D4 selectivity; also 5-HT2A/2C antagonist 50 mg500 mg

Other 3788 L-DOPA Dopamine precursor 50 mg

Dopamine Transporters

Inhibitors 0513 GBR 12783 Potent and selective DA uptake inhibitor 10 mg50 mg

0421 GBR 12909 Selective DA uptake inhibitor; also σ ligand 10 mg50 mg

δ Opioid Receptors

Agonists 1431 DPDPE Selective δ agonist 1 mg

0764 SNC 80 Highly selective non-peptide δ agonist 10 mg50 mg

Antagonists 0740 Naltrindole Selective non-peptide δ antagonist 10 mg50 mg

Modulators 5983 BMS 986187 Potent positive allosteric modulator of δ receptors 10 mg50 mg

Fatty Acid Amide Hydrolase (FAAH)

Inhibitors 4355 TC-F 2 Potent, reversible and selective FAAH inhibitor 10 mg50 mg

4612 URB 597 Potent and selective FAAH inhibitor 10 mg50 mg

GABAA Receptors

Agonists 3250 L-838,417 GABAA partial agonist; displays subtype selectivity 10 mg50 mg

0289 Muscimol Potent GABAA agonist; also GABAA-ρ partial agonist 1 mg10 mg50 mg

Antagonists 2503 (-)-Bicuculline methiodide Water-soluble GABAA antagonist 10 mg50 mg

1128 Picrotoxin GABAA antagonist 1 g

1262 SR 95531 Competitive and selective GABAA antagonist 10 mg50 mg

Benzodiazepines 1328 Flumazenil Benzodiazepine antagonist 10 mg50 mg

1327 L-655,708 Benzodiazepine inverse agonist; selective for α5-containing GABAA receptors

10 mg50 mg

0655 Zolpidem Benzodiazepine agonist 10 mg50 mg



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Modulators 3653 Allopregnanolone Positive allosteric modulator of GABAA receptors 10 mg

2867 Flupirtine GABAA modulator; also indirect NMDA antagonist and Kv7 channel activator 10 mg50 mg

2531 Ganaxolone Potent positive allosteric modulator of GABAA receptors 10 mg50 mg

Others 1471 Etomidate GABA-mimetic; selectively interacts with β2- and β3-subunit containing GABAA receptors

10 mg50 mg

GABAA-ρ Receptors

Antagonists 0379 SKF 97541 GABAA-ρ antagonist; also highly potent GABAB agonist 10 mg50 mg

0807 THIP GABAA-ρ antagonist; also GABAA agonist 50 mg

1040 TPMPA Selective GABAA-ρ antagonist 10 mg50 mg

GABAB Receptors

Agonists 0796 (R)-Baclofen Selective GABAB agonist; active enantiomer of (RS)-Baclofen (Cat. No. 0417)

10 mg50 mg

Antagonists 1246 CGP 52432 Potent and selective GABAB antagonist 10 mg50 mg

1088 CGP 54626 Potent and selective GABAB antagonist 10 mg50 mg

1248 CGP 55845 Potent and selective GABAB antagonist 10 mg50 mg

Modulators 1513 CGP 7930 Positive allosteric modulator of GABAB receptors 10 mg50 mg

GABA Miscellaneous Compounds

Other 0344 GABA Endogenous agonist 1 g

0806 Gabapentin Increases brain GABA; anticonvulsant 10 mg50 mg

GABA Transporters

Inhibitors 1779 NNC 711 Selective GAT-1 inhibitor 10 mg50 mg

0768 Riluzole GABA uptake inhibitor; also inhibits glutamate release and blocks NaV channels

25 mg

1561 (S)-SNAP 5114 GABA uptake inhibitor 10 mg50 mg

Glutamate Transporters

Inhibitors 0111 Dihydrokainic acid EAAT2 (GLT-1)-selective non-transportable inhibitor of L-glutamate and L-aspartate uptake

1 mg10 mg50 mg

1223 DL-TBOA Selective non-transportable inhibitor of EAATs 10 mg50 mg

2532 TFB-TBOA High affinity EAAT1 and EAAT2 blocker 1 mg10 mg

2652 WAY 213613 Potent, non-substrate EAAT2 inhibitor 10 mg50 mg

GPR55

Agonists 1297 Abn-CBD Selective GPR55 agonist; neurobehaviorally inactive 10 mg

2797 O-1602 Potent GPR55 agonist 10 mg

Antagonists 4959 CID 16020046 Selective GPR55 antagonist 5 mg25 mg

G Proteins (Heterotrimeric)

Inhibitors 5642 CMPD101 Potent and selective GRK2/3 inhibitor 10 mg

3090 Gallein Inhibitor of βγ signaling 50 mg

Other 3097 Pertussis Toxin Catalyzes ADP-ribosylation of Gi, Go and Gt 50 µg



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Hydroxylases

Inhibitors 0938 p-Chlorophenylalanine Tryptophan hydroxylase inhibitor 100 mg

IP3 Receptors

Antagonists 1224 2-APB IP3 receptor antagonist; also TRP channel modulator 10 mg50 mg

Others 1280 (-)-Xestospongin C Reported inhibitor of IP3-dependent Ca2+ release 10 µg

Kainate Receptors

Agonists 0269 Domoic acid Potent and selective kainate agonist 1 mg

0222 Kainic acid Kainate agonist; excitant and neurotoxin 1 mg10 mg50 mg

Antagonists 2728 ACET Potent kainate antagonist; displays selectivity for GluK1-containing receptors

10 mg

1045 CNQX disodium salt Potent non-NMDA iGluR antagonist; more water soluble form of CNQX (Cat. No. 0190)

1 mg10 mg50 mg

3621 UBP 310 GluK1-selective kainate antagonist 10 mg50 mg

κ Opioid Receptors

Agonists 3195 Dynorphin A Endogenous κ agonist 1 mg

5519 (-)-Pentazocine κ agonist; antinociceptive 10 mg

0495 (±)-U-50488 Selective κ agonist 25 mg

Antagonists 0794 DIPPA Selective and irreversible κ antagonist 10 mg50 mg

0347 nor-Binaltorphimine Selective κ antagonist 10 mg50 mg

Ketamine and Metabolites

5982 cis-6-Hydroxynorketamine Enhances AMPA currents: antidepressant 10 mg50 mg

6094 2R,6R-Hydroxynorketamine Enhances AMPA currents; decreases D-serine (a NMDA co-agonist); lacks ketamine-related side effects

10 mg

6095 2S,6S-Hydroxynorketamine Decreases D-serine (a NMDA co-agonist); antidepressant 10 mg

3131 Ketamine Non-competitive NMDA antagonist 50 mg

4379 (S)-(+)-Ketamine NMDA antagonist; enantiomer of ketamine (Cat. No. 3131); neuroprotective.

50 mg

1970 Norketamine Potent non-competitive NMDA antagonist; antinociceptive 10 mg50 mg

5996 (R)-Norketamine NMDA receptor modulator; metabolite of ketamine (Cat. No. 3131) 10 mg

6112 (S)-Norketamine NMDA receptor modulator; metabolite of ketamine (Cat. No. 3131) 10 mg

MAGL

Inhibitors 3836 JZL 184 Potent MAGL inhibitor 10 mg50 mg

4872 KML 29 Highly potent and selective MAGL inhibitor 10 mg50 mg

Metabotropic Glutamate Receptors

Agonists 2385 AMN 082 Selective mGlu7 agonist 10 mg50 mg

3695 CHPG Sodium salt Selective mGlu5 agonist; sodium salt of CHPG (Cat. No. 1049) 10 mg50 mg

1302 (S)-3,4-DCPG Potent and selective mGlu8a agonist 10 mg50 mg

0975 DCG IV Highly potent group II mGlu agonist; also NMDA agonist 1 mg10 mg50 mg



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0805 (S)-3,5-DHPG Selective group I mGlu agonist; active enantiomer of 3,5-DHPG (Cat. No. 0342)

5 mg10 mg

0103 L-AP4 Selective group III mGlu agonist 1 mg10 mg50 mg

0188 L-Quisqualic acid Group I mGlu agonist; also AMPA agonist 1 mg10 mg50 mg

5064 LY 379268 disodium salt Selective group II mGlu agonist; sodium salt of LY 379268 (Cat. No. 2453) 10 mg50 mg

Antagonists 0972 CPPG Potent group III mGlu antagonist 5 mg25 mg

2333 JNJ 16259685 Highly potent, mGlu1-selective non-competitive antagonist 10 mg50 mg

4062 LY 341495 disodium salt Potent and selective group II mGlu antagonist; disodium salt of LY 341495 (Cat. No. 1209)

1 mg10 mg50 mg

1237 LY 367385 Selective mGlu1a antagonist 10 mg50 mg

2963 MMPIP Potent and selective allosteric mGlu7 antagonist 1 mg10 mg50 mg

1212 MPEP Potent mGlu5 antagonist; positive allosteric modulator of mGlu4 receptors 10 mg50 mg

2921 MTEP Potent and selective mGlu5 antagonist 10 mg50 mg

Modulators 4416 ADX 10059 Negative allosteric modulator of mGlu5 receptors 10 mg50 mg

4048 BINA Selective positive allosteric modulator of mGlu2 receptors 10 mg50 mg

3283 LY 487379 Selective positive allosteric modulator of mGlu2 receptors 10 mg50 mg

4982 ML 337 Selective negative allosteric modulator of mGlu3 receptors 10 mg50 mg

4323 VU 0360172 Positive allosteric modulator of mGlu5 receptors 10 mg50 mg

5377 VU 0483605 Positive allosteric modulator of mGlu1 receptors 10 mg50 mg

Monoamine Oxidase

Inhibitors 1095 (R)-(-)-Deprenyl MAO-B inhibitor 1 g

4395 Moclobemide Reversible MAO-A inhibitor 10 mg50 mg

4308 Rasagiline Selective and irreversible MAO-B inhibitor 50 mg

µ Opioid Receptors

Agonists 1171 DAMGO Selective μ agonist 1 mg

1055 Endomorphin-1 Potent and selective μ agonist 5 mg

Antagonists 1560 CTAP Potent and selective μ antagonist 1 mg

1578 CTOP Potent and selective μ antagonist 1 mg

0926 β-Funaltrexamine Irreversible and selective μ antagonist 10 mg50 mg


32 |

NMDA Receptors

Agonists 3406 GLYX 13 NMDA partial agonist; acts at the glycine site 1 mg

0114 NMDA Selective NMDA agonist 50 mg500 mg

Antagonists 0247 (R)-CPP Potent NMDA antagonist; more active enantiomer of (RS)-CPP (Cat. No. 0173)

10 mg50 mg

0106 D-AP5 Potent and selective NMDA antagonist; more active form of DL-AP5 (Cat. No. 0105)

1 mg10 mg50 mg100 mg

0773 Memantine NMDA antagonist; acts at ion channel site 50 mg

0924 (+)-MK 801 Non-competitive NMDA antagonist; acts at ion channel site 10 mg50 mg

5018 PEAQX Potent and GluN2A-selective NMDA antagonist 10 mg

4801 QNZ 46 GluN2C/GluN2D-selective NMDA non-competitive antagonist 10 mg50 mg

1594 Ro 25-6981 GluN2B-selective NMDA antagonist 1 mg10 mg50 mg

4154 TCN 201 GluN1/GluN2A-selective NMDA antagonist 10 mg50 mg

NOP Receptors

Agonists 0910 Nociceptin Endogenous NOP agonist 1 mg

3240 SCH 221510 Potent and selective NOP agonist 10 mg50 mg

Antagonists 2598 (±)-J 113397 Potent and selective NOP antagonist 10 mg50 mg

3573 SB 612111 Selective NOP antagonist 10 mg50 mg

Opioid Receptors: Non-selective Compounds

Agonists 1889 [Leu5]-Enkephalin Endogenous opioid agonist 25 mg

Antagonists 0599 Naloxone Non-selective opioid antagonist 100 mg

0677 Naltrexone Non-selective opioid antagonist 100 mg

Other 3137 Neuropeptide FF Antiopioid neuropeptide; endogenous NPFF1 and NPFF2 agonist 1 mg

Phospholipase C

Activators 1941 m-3M3FBS Phospholipase C activator 10 mg

Inhibitors 1437 D609 Selective PC-PLC inhibitor 10 mg50 mg

1842 RHC 80267 Diacylglycerol lipase inhibitor 10 mg50 mg

1268 U 73122 Phospholipase C inhibitor 10 mg50 mg

Purinergic (P2X) Receptors

Agonists 3312 BzATP P2X7 agonist; also P2X1 and P2Y1 partial agonist 1 mg

Antagonists 3579 5-BDBD Potent P2X4 antagonist 10 mg50 mg

2972 A 438079 Competitive P2X7 antagonist 10 mg50 mg

5545 BX 430 Selective P2X4 allosteric antagonist 10 mg50 mg

5299 JNJ 47965567 Potent and selective P2X7 antagonist; brain penetrant 10 mg50 mg



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2548 NF 110 Potent P2X3 antagonist 10 mg50 mg

1391 NF 449 Highly selective P2X1 antagonist 10 mg50 mg

Purinergic (P2Y) Receptors

Agonists 1624 2-Methylthioadenosine diphosphate

Potent agonist at P2Y1, P2Y12 and P2Y13 10 mg

2157 MRS 2365 Highly potent and selective P2Y1 agonist 1 mg

2502 MRS 2693 trisodium salt Selective P2Y6 agonist 1 mg

3892 NF 546 Selective P2Y11 agonist 10 mg

3280 2-ThioUTP tetrasodium salt Potent and selective P2Y2 agonist 1 mg

Antagonists 4890 AR-C 118925XX Selective and competitive P2Y2 antagonist 5 mg

0900 MRS 2179 tetrasodium salt Selective P2Y1 antagonist 10 mg50 mg

2159 MRS 2500 Highly potent and selective P2Y1 antagonist 1 mg

2146 MRS 2578 Selective P2Y6 antagonist 10 mg50 mg

3983 PSB 0739 Highly potent P2Y12 antagonist 10 mg50 mg

Purinergic Receptors Non-selective compounds

Agonists 4080 ATPγS tetralithium salt Non-selective P2 agonist; analog of ATP (Cat. No. 3245) 10 mg

1062 2-Methylthioadenosine triphosphate

Non-selective P2 agonist 10 mg

3209 α,β-Methyleneadenosine 5ʹ-triphosphate

Non-selective P2 agonist 10 mg

Antagonist 0625 PPADS tetrasodium salt Non-selective P2 antagonist 10 mg50 mg

Vesicular Monoamine Transporters

Inhibitors 2742 Reserpine Inhibitor of vesicular monoamine transport 1 g

2175 Tetrabenazine Potent inhibitor of vesicular monoamine transport 10 mg50 mg

Others 5911 FFN 200 Selective fluorescent VMAT2 substrate 10 mg

5043 FFN 206 Fluorescent VMAT2 substrate 10 mg



34 |

Further Reading and Featured Publications

Dopaminergic Transmission

Beaulieu etal. (2015) Dopamine receptors – IUPHAR Review 13. BrJPharmacol. 172, 1.Bertler&Rosengren (1959) Occurrence and distribution of dopamine in brain and other tissues. Experientia. 15, 10. Eisenhofer etal. (2004) Catecholamine metabolism: a contemporary view with implications for physiology and medicine. PharmacolRev. 56, 331. Kebabian&Calne (1979) Multiple receptors for dopamine. Nature. 277, 93. Laverty&Taylor (1970) Effects of intraventricular 2,4,5-trihydroxyphenylethylamine (6-hydroxydopamine) on rat behavior and brain catecholamine metabolism. BrJPharmacol. 40, 836. Marsden (2006) Dopamine: the rewarding years. BrJPharmacol. 147, S136.

Glutamatergic Transmission

Anderson&Swanson (2000) Astrocyte glutamate transport: review of properties, regulation, and physiological functions. Glia. 32, 1. Curtis&Watkins (1965) The pharmacology of amino acids related to gamma-aminobutyric acid. PharmacolRev. 17, 347. MacDermott etal. (1986) NMDA-receptor activation increases cytoplasmic calcium concentration in cultured spinal cord neurones. Nature. 321, 519. McCulloch etal. (1974) The differential sensitivity of spinal interneurones and Renshaw cells to Kainate and N-methyl-D-aspartate. ExpBrainRes. 21, 515. Nakanishi (1992) Molecular diversity of glutamate receptors and implications for brain function. Science. 258, 597. Nicolettietal.(2011) Metabotropic glutamate receptors: from the workbench to the bedside. Neuropharmacology. 60, 1017.Traynelis etal. (2010) Glutamate receptor ion channels: structure, regulation and function. PharmacolRev. 62, 405. Watkins&Jane (2006) The glutamate story. BrJPharmacol. 147, S100.

Opioid Peptide Transmission

Fengetal. (2012) Current research on opioid receptor function. CurrDrugTargets. 13, 230. Kelly (2013) Efficacy and ligand bias at the µ-opioid receptor. BrJPharmacol. 169, 1430. Noble etal. (2015) The opioid receptors as targets for drug abuse medication. BrJPharmacol. 172, 3964.Schwarzer (2009) 30 years of dynorphins – new insights on their functions in neuropsychiatric diseases. PharmacolTher. 123, 353.Toll etal. (2016) Nociceptin/Orphanin FQ receptor structure, signaling, ligands, functions, and interactions with opioid systems. PharmacolRev. 68, 419.

Serotonergic Transmission

Bradley etal. (1986) Proposals for the classification and nomenclature of functional receptors for 5-hydroxytryptamine. Neuropharmacology. 25, 563. Blakely etal. (1994) Molecular physiology of norepinephrine and serotonin transporters. JExpBiol. 196, 263. Hannon&Hoyer (2008) Molecular biology of 5-HT receptors. BehavBrainRes. 195, 198. Twarog&Page (1953) Serotonin content of some mammalian tissues and urine and a method for its determination. AmJPhysiol. 175, 157. Yohn etal. (2017) The role of 5-HT receptors in depression. MolBrain. 10, 28.

Chemogenetics

Campbell&Marchant(2018) The use of chemogenetics in behavioural neuroscience: receptor variants, targeting approaches and caveats. BrJPharmacol.175, 994.Sternson&Roth(2014) Chemogenetic tools to interrogate brain functions. AnnuRevNeurol.37, 387.Vardy etal. (2016) A new DREADD facilitates the multiplex chemogenetic interrogation of behavior. Neuron.86, 936.


www.tocris.com | 35

Depression

Carretal. (2010) Antidepressant-like effects of kappa-opioid receptor antagonists in Wistar Kyoto rats. Neuropsychopharmacology. 35, 752.McLaughlinetal. (2006a) Prior activation of kappa opioid receptors by U50,488 mimics repeated forced swim stress to potentiate cocaine place preference conditioning. Neuropsychopharmacology. 31, 787.McLaughlinetal. (2006b) Social defeat stress-induced behavioral responses are mediated by the endogenous kappa opioid system. Neuropsychopharmacology. 31, 1241.Pare(1992) The performance of WKY rats on three tests of emotional behavior. PhysiolBehav.51, 1051.Pare(1994) Openfield, learned helplessness, conditioned defensive burying, and forced-swim tests in WKY rats. PhysiolBehav.55, 433.Pearsonetal. (2006) Identifying genes in monoamine nuclei that may determine stress vulnerability and depressive behavior in Wister-Kyoto rats. Neuropsychopharmacology. 31, 2449.Pringleetal. (2011) A cognitive neuropsychological model of antidepressant drug action. ProgNeuropyschopharmacolBiolPsychiatry.35, 1586.Stuartetal. (2013) A translational rodent assay of affective biases in depression and antidepressant therapy. Neuropsychopharmacology. 38, 1625.

Ketamine Metabolites in Depression

Berman etal. (2000) Antidepressant effects of ketamine in depressed patients. BiolPsychiatry. 47, 351. Holtman etal. (2008) Effects of norketamine enantiomers in rodent models of persistent pain. PharmacolBiochemBehav. 90, 676. Zanos etal. (2016) NMDAR inhibition-independent antidepressant actions of ketamine metabolites. Nature. 533, 481. Zarate etal. (2006) A randomized trial of an N-methyl-D-aspartate antagonist in treatment-resistant major depression. ArchGenPyschiatry. 62, 856.

Addiction

Baler&Volkow(2006) Drug addiction: the neurobiology of disrupted self-control. TrendsMolMed. 12,559.Ferraroetal. (2010a) A novel mechanism of cocaine to enhance dopamine D2-like receptor mediated neurochemical and behavioral effects. An invivoand invitrostudy. Neuropsychopharmacology. 37, 1856.Ferraroetal. (2010b) Nanomolar concentrations of cocaine enhance D2-like agonist-induced inhibition of K+-evoked [3H]-dopamine efflux from rat striatal synaptosomes: a novel action of cocaine. JNeuralTransm.117, 593.Marchantetal.(2010) Medial dorsal hypothalamus mediated the inhibition of reward seeking after extinction. JNeurosci.30, 14102.Rice&Cragg(2008) Dopamine spillover after quantal release: rethinking dopamine transmission in the nigrostriatal pathway. BrainResRev.58, 303.

Epilepsy

Goldman&Coulter(2013) Mechanisms of epileptogenesis: a convergence on neuronal circuit dysfunction. NatRevNeurosci.14, 337.Klatteetal.(2013) Impaired D-serine-mediated cotransmission mediates cognitive dysfunction in epilepsy. JNeurosci.33, 13066.

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