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8/3/2019 Fu-Ming Zhou and John J. Hablitz- Activation of Serotonin Receptors Modulates Synaptic Transmission in Rat Cerebr

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82:2989-2999, 1999.J NeurophysiolFu-Ming Zhou and John J. Hablitz

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Activation of Serotonin Receptors Modulates Synaptic Transmission

in Rat Cerebral Cortex

FU-MING ZHOU AND JOHN J. HABLITZDepartment of Neurobiology, University of Alabama, Birmingham, Alabama 35294

Zhou, Fu-Ming and John J. Hablitz. Activation of serotonin receptorsmodulates synaptic transmission in rat cerebral cortex. J. Neurophysiol.82: 29892999, 1999. The cerebral cortex receives an extensive seroto-nergic (5-hydroxytryptamine, 5-HT) input. Immunohistochemical studiessuggest that inhibitory neurons are the main target of 5-HT innervation.In vivo extracellular recordings have shown that 5-HT generally inhibitedcortical pyramidal neurons, whereas in vitro studies have shown anexcitatory action. To determine the cellular mechanisms underlying thediverse actions of 5-HT in the cortex, we examined its effects on corticalinhibitory interneurons and pyramidal neurons. We found that 5-HT,through activation of 5-HT

2Areceptors, induced a massive enhancement

of spontaneous inhibitory postsynaptic currents (sIPSCs) in pyramidalneurons, lasting for6 min. In interneurons, this 5-HT-induced enhance-ment of sIPSCs was much weaker. Activation of 5-HT

2Areceptors also

increased spontaneous excitatory postsynaptic currents (sEPSCs) in py-ramidal neurons. This response desensitized less and at a slower rate. Incontrast, 5-HT slightly decreased evoked IPSCs (eIPSCs) and eEPSCs. Inaddition, 5-HT via 5-HT

3receptors evoked a large and rapidly desensi-

tizing inward current in a subset of interneurons and induced a transientenhancement of sIPSCs. Our results suggest that 5-HT has widespreadeffects on both interneurons and pyramidal neurons and that a short pulseof 5-HT is likely to induce inhibition whereas the prolonged presence of5-HT may result in excitation.

I N T R O D U C T I O N

Serotonin (5-hydroxytryptamine, 5-HT) is an important en-dogenous neuromodulator in the CNS (Baumgarten andGrozdanovic 1997; Jacobs and Azmitia 1992). Since the dis-covery of brain 5-HT pathways in the 1960s (Dahlstrom andFuxe 1964), 5-HT has been implicated in drug-induced psy-choses and a number of psychiatric disorders, major depres-sion, and schizophrenia in particular (Abi-Dargham et al. 1997;Blier and De Montigny 1997). Histochemical studies haveshown that the mammalian cerebral cortex receives an exten-sive 5-HT input originating from midbrain raphe 5-HT neurons(Jacobs and Azmitia 1992; Tork 1990). GABAergic inhibitoryneurons appear to be the principal cortical target of 5-HT fibers(DeFelipe et al. 1991; Hornung and Celio 1992; Smiley and

Goldman-Rakic 1996), suggesting a potential role of GABAer-gic neurons in functioning of the 5-HT system.

5-HT receptors comprise a complex family. On the basis oftheir pharmacology, signal transduction mechanisms and mo-lecular structure, more than a dozen types of 5-HT receptorshave been identified (Hoyer et al. 1994). Most of these recep-tors are coupled to various G proteins with the exception of the5-HT

3receptor, which is a ligand gated cation channel

(Derkach et al. 1989; Jackson and Yakel 1995; Maricq et al1991). Multiple 5-HT receptor subtypes are expressed in thecerebral cortex (Mengod et al. 1997). In cerebral cortex, 5-HT3receptors are only expressed in inhibitory neurons (Moraleand Bloom 1997) whereas 5-HT

2Areceptors are heavily ex

pressed in pyramidal cells and to a lesser extent in inhibitoryneurons (Hamada et al. 1998; Jakab and Goldman-Rakic 1998Willins et al. 1997).

Since the 1960s, many experiments using in vivo microiontophoretic methods have characterized how 5-HT affects neu

ronal behavior. The predominant effect of 5-HT on cerebracortical pyramidal neurons is an inhibition of spontaneouspiking, but the underlying mechanism is not clear (see Jacoband Azmitia 1992; Phillis 1984; Reader and Jasper 1984 foreview). However, intracellular studies in rat cortical slicesuggested that 5-HT induces depolarization and action potential firing in pyramidal cells (Araneda and Andrade 1991Davies et al. 1987; Tanaka and North 1993). FurthermoreAghajanian and Marek (1997) reported that 5-HT enhancespontaneous excitatory postsynaptic currents (sEPSCs) withousignificantly changing spontaneous inhibitory postsynapticcurrents (sIPSCs) in frontal pyramidal neurons. These in vitroresults suggest that 5-HT is mainly excitatory in cortical neuronal circuitry.

The present study directly compares the effects of 5-HT onEPSCs and IPSCs in cortical inhibitory neurons and pyramidacells. We paid particular attention to layer I neurons becausethese neurons are mostly GABAergic and layer I receives adense 5-HT innervation (DeFelipe et al. 1991; Gabbott andSomogyi 1986; Hornung and Celio 1992; Hornung et al. 1990Lidov et al. 1980; Mulligan and Tork 1988; Smiley and Gold-man-Rakic 1996). We found that in pyramidal neurons 5-HTinduces a robust and desensitizing enhancement of sIPSCs anda weaker and longer-lasting enhancement of sEPSCs through5-HT

2Areceptor activation. 5-HT also induced a rapidly de-

sensitizing direct inward current through activation of 5-HTreceptors in a small subset of cortical interneurons. Our result

suggest that a short pulse of 5-HT released under physiologicaconditions is likely to have an inhibitory effect on corticaneuronal circuitry.

M E T H O D S

Slice preparation

Brain slices were prepared according to methods described previously(Zhou and Hablitz 1996a). Briefly, 9- to 28-day-old Sprague-Dawley ratwere decapitated, and the brains were dissected out in 1 min. Theisolated brain was immersed immediately in ice-cold saline. Brain slices

The costs of publication of this article were defrayed in part by the paymentof page charges. The article must therefore be hereby marked advertisementin accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

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(300-m thick) were cut from frontal and anterior cingulate areas (Paxi-nos and Watson 1986) on a Vibratome. Slices were placed in a storagechamber at room temperature (2224C). During recordings individualslices were transferred to a microscope mounted chamber where theywere perfused at a rate of 3 ml/min. The normal bathing solutioncontained (in mM) 125 NaCl, 3.5 KCl, 2.5 CaCl

2, 1.3 MgCl

2, 26

NaHCO3

, and 10 D-glucose. The bathing solution was continuouslybubbled with 95% O

2-5% CO

2to maintain pH around 7.4.

Whole cell recording

Individual neurons were visualized using an Olympus BX50WIupright microscope equipped with Nomarski optics, a 40 waterimmersion lens and a Hamamatsu Newvicon video camera. Layer Ineurons were identified reliably during recording by their locationbelow the pial surface (Zhou and Hablitz 1996a). Fast-spiking inter-neurons in layers II/III were identified by their nonpyramidal appear-ance and fast-spiking characteristics. Pyramidal neurons (layers II-VI)were identified by their pyramidal shape, prominent apical dendrites,and regular spiking properties. All recordings were made at roomtemperature. Patch electrodes were prepared from Garner KG-33 glasstubing using a Narishige PP-83 puller. Electrodes were coated withsilicone elastomer (Sylgard). Series resistance (R

s) was estimated

according to Rs

10 mV/I, where I was the current (filtered

10kHz) evoked by a 10-mV pulse when the pipette capacitance was fullycompensated. During recordings, Rs was 415 M among differentcells and was not compensated. Care was exercised to monitor theconstancy of the series resistance, and recordings were terminatedwhenever Rs was15 M or a significant increase (20%) occurred.The intracellular solutions contained (in mM) 135 CsCl or KCl, 10HEPES, 2 Mg-ATP, 0.2 Na-GTP, and 0.5 EGTA. pH and osmolaritywere adjusted to 7.3 and 280 mOsm, respectively. About 50% ofvoltage-clamp experiments were performed using the CsCl-basedintracellular solution, and the rest were conducted with the KCl-basedintracellular solution. No difference was observed in 5-HT effectswith the use of these two intracellular solutions. Current-clamp ex-periments used only the KCl-based intracellular solution. Tight seals(5 G before breaking into whole cell mode) were achieved withoutcleaning the cell. Before forming tight seals, all offsets were nulledusing the offset feature of the patch amplifier. To examine evokedsynaptic responses in layers IV and V pyramidal neurons, a stainlesssteel bipolar electrode was placed 200 m lateral to the recordedcells. Electrical stimuli were controlled by a Grass stimulator-isolatorsystem.

Electrical signals were recorded using an Axopatch-200A amplifier(Axon Instruments), stored on videotape, and analyzed off-line. Digi-tization and analysis of the records were achieved using SCANsoftware (courtesy of J. Dempster, University of Strathclyde, Glas-gow, UK). Spontaneous and miniature synaptic events were defined asthose recorded in the absence and presence of 0.3 M tetrodotoxin(TTX), respectively. Frequencies of synaptic events were calculatedas the reciprocals of interevent intervals. The decay of synapticcurrents was fitted to double exponential functions. Statistical com-parisons of the frequency and amplitude of synaptic currents before,during, and after 5-HT were made using the Kolmogorov-Smirnov(K-S) test. P 0.01 was considered significant. Numerical values areexpressed as mean SD. About two-thirds of the cells were recordedin the shoulder region or Fr2 region of the frontal cortex and the restwere in the anterior cingulate cortex (Paxinos and Watson 1986).Because no difference was observed among cells from the two areas,data were pooled.

Bicuculline methiodide (Bic) (10 M) was used to blockGABA

Areceptor-mediated synaptic events whereas ionotropic

glutamate receptors were blocked by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) (10 M) and D(-)2-amino-5-phosphonovalericacid (D-APV) (20 M). 5-HT, -methyl-5-HT, 1-(m-chlorophe-

nyl)-biguanide (mCPBG), and risperidone were obtained fromResearch Biochemical International (Natick, MA).

R E S U L T S

5-HT induces an enhancement of sIPSCs in neocorticalpyramidal cells

Bath application of 40 M 5-HT induced an enhancemen

of sIPSCs recorded in pyramidal cells. Specimen recordsunder control conditions and during application of 5-HT areshown in Fig. 1, A and B, respectively. The effects of 5-HTlasted for 6 min (range 310 min), as shown in Fig. 1CDuring the 2-min period of peak 5-HT enhancement, sIPSCfrequency and amplitude were increased by 810 260%and 110 45%, respectively (n 38). The kinetics osIPSCs were not altered by 5-HT. Depending on recordingconditions, the 1090% rise time was 0.51 ms, and thedouble exponential decay had a fast time constant of 2 4 mand a slower time constant of 1020 ms, similar to thosedescribed previously (Zhou and Hablitz 1997b). In the presence of 5-HT, there were more large-amplitude events al-though small-amplitude events also were increased. Theffect of 5-HT declined in the continued presence of theagonist. Dose-response relations were not studied due to thelong time needed for a full recovery. However, 10 M 5-HTwas not able to reliably induce a large sIPSC enhancementwhereas the responses induced by 40 and 100 M 5-HTwere indistinguishable, indicating that 40 M was a nearlysaturation concentration. Events recorded under our recording conditions (20 M D-APV, 10 M CNQX, up to 100M 5-HT, symmetric Cl and a holding potential of70mV) were sIPSCs because all events were blocked by 10M Bic in three cells tested (see also Zhou and Hablitz1997b).

5-HT2A receptors enhance sIPSCs in pyramidal cells

5-HT2A

receptors are expressed abundantly in the cortex(Wright et al. 1995). To examine if activation of thesreceptors could increase sIPSC frequency in pyramidacells, the 5-HT

2-specific agonist -methyl-5-HT (Baxter e

al. 1995; Sheldon and Aghajanian 1990) was bath appliedIn all pyramidal neurons tested (n 25), 20 M -methyl5-HT produced an enhancement of sIPSCs similar to thainduced by 5-HT (Fig. 2). The mean frequency and ampli-tude of sIPSCs were increased by 820 180% and 115 42% over control levels, respectively. The kinetics of sIPSCswere not altered by -methyl-5-HT. The enhancing effect o-methyl-5-HT also declined over time, lasting from 3 to 10min among different cells. We also tested the selective5-HT

2Aantagonist, risperidone (Baxter et al. 1995). Be

cause of the desensitization, experiments attempting to apply risperidone (10 M) after an -methyl-5-HT-inducedenhancement of sIPSCs were inconclusive. Therefore wepreincubated brain slices with 5 or 10 M risperidone. Withthis treatment, -methyl-5-HT failed to induce any significant change of sIPSCs in six pyramidal neurons from sixslices. In two additional pyramidal neurons, pretreatmenwith risperidone also rendered 40 M 5-HT ineffective inenhancing sIPSCs. These results indicate that 5-HT en

2990 F.-M. ZHOU AND J. J. HABLITZ


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hancement of sIPSCs in pyramidal cells was mediated byactivation of 5-HT

2Areceptors on GABAergic interneurons.

We sought to determine the mechanism underlying the5-HT

2Areceptor enhancement of sIPSCs. Under the somatic

recording conditions employed, -methyl-5-HT induced nodetectable direct inward current in layer I neurons (n 20) orlayer II/III fast-spiking interneurons (n 3). In current-clamprecordings, -methyl-5-HT failed to induce a significant depo-larization or increase in spontaneous firing in seven layer Ineurons tested. -methyl-5-HT also failed to alter input resis-tance under either voltage- or current-clamp conditions. Nohyperpolarization or outward current was induced by 5-HT or-methyl-5-HT in any of the cells recorded in this study.

Furthermore despite the enhancement of sIPSCs, bath applica-tion of 5-HT (n 4) or -methyl-5-HT (n 2) did not induceany detectable change in the frequency or amplitude of min-iature IPSCs (mISPCs) recorded in the presence of 0.3 MTTX (Fig. 3).

Activation of 5-HT2A

receptors enhances sIPSCsin interneurons

Layer I neurons receive GABAergic inputs (Zhou andHablitz 1997b). Our results presented in the preceding sec-

tion suggest that serotonergic activation may enhance thiGABAergic input to layer I neurons. To test this idea, westudied the effects of 5-HT on sIPSCs recorded in layer neurons. 5-HT (40100 M) produced an enhancement osIPSCs in 37/52 layer I neurons. As shown in Fig. 4-methyl-5-HT (20 M) also increased sIPSCs in layer Ineurons (15/20). The sIPSC enhancement in layer I neuronwas also desensitizing. However, the percentage increasein frequency (90 48%) and amplitude (46 37%) in layeI neurons were lower than those in pyramidal neuronsSimilarly, -methyl-5-HT did not induce any significanenhancement of sIPSCs in four layer I neurons from fourslices preincubated with 10 M risperidone, indicating an

involvement of 5-HT2A receptors.

Contribution of 5-HT3

receptors

In other cell systems, 5-HT3

receptors are coupled to cationchannels conducting inward currents under physiological conditions (Jackson and Yakel 1995; Kawa 1994; McMahon and Kaue1997). A recent immunohistochemical study indicated that 5-HTreceptors are expressed only in a subset of inhibitory neurons incerebral cortex (Morales and Bloom 1997). Therefore we rea

FIG. 1. Serotonin (5-HT)-induced enhancement of spontaneous inhibitory postsynaptic potentials (sIPSCs) in pyramidaneurons. Recordings were made from an 18-day-old frontapyramidal neuron at 70 mV. Bathing solution contained 20M D(-)2-amino-5-phosphonovaleric acid (D-APV) and 10 M6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) but no TTX. AsIPSCs recorded under control condition. Mean interevent interval and amplitude during the control period were 0.58 s (1.7Hz) and 40 pA, respectively. B: bath application of 40 M5-HT-enhanced sIPSCs. Mean interevent interval was decreased to 60 ms (17 Hz) for the first 4 min. Mean amplitudewas only increased to 95 pA. C: scatter plot showing the changeof interevent interval of sIPSCs induced by 5-HT and th

desensitization of this effect during the entire recording.

2995-HT RECEPTORS IN CORTICAL INTERNEURONS


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soned that activation of these 5-HT3

receptors might induce atransient enhancement of sIPSCs through a direct excitation ofinhibitory neurons. Indeed, in 4 of 52 layer I cells, bath applicationof 40100M 5-HT induced a burst-like enhancement of sIPSCs,lasting for 520 s. The rapid desensitization of this enhancementis indicative of 5-HT

3receptor involvement. Therefore we tested

the specific 5-HT3

receptor agonist, mCPBG. In 2 of 21 layer Icells and in 2 of 19 pyramidal neurons, bath application of 40 or100 M mCPBG also induced a brief enhancement of sIPSCs inthe absence TTX (Fig. 5). The similarity of 5-HT and mCPBGresponses suggests that the transient enhancement of sIPSCs wasmediated by activation of 5-HT

3receptors in inhibitory neurons

FIG. 2. -methyl-5-HT enhances sIPSCs inpyramidal neurons. Recordings were made froma 17-day-old frontal pyramidal neuron at 70mV in the presence of 20 M D-APV and 10 MCNQX but no TTX. A: sIPSCs recorded undecontrol condition. Mean interevent interval andamplitude during the control period were 0.6 (1.7 Hz) and 40 pA, respectively. B: bath application of 20 M -methyl-5-HT enhanced sIPSCs. Mean interval was decreased to 65 ms (15Hz). Mean amplitude was only increased to 78pA. C: enhancing effect of -methyl-5-HT onsIPSCs started to decline in 6 min; sIPSCdeclined to near control level in 10 min. D and

E: scatter plots showing the effects of-methyl5-HT on sIPSC interevent interval and amplitudeduring the entire recording.

FIG. 3. 5-HT had no effect on miniature IPSCs in cortical neurons. Recordings were made from a 17-day-old anterior cingulatpyramidal neuron at 70 mV in the presence of 20 M D-APV, 10M CNQX, and 0.3 M TTX. A: cumulative probability plot indicating that the distribution of mIPSC interevent intervals was noaltered by 100 M 5-HT. B: cumulative probability plot indicatingthat the distribution of mIPSC amplitude was not altered by 100 M5-HT.



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Activation of 5-HT3

receptors induces a desensitizing inwardcurrent in interneurons

Interneurons were examined for a 5-HT3-receptor-mediated

inward current. Indeed, as shown in Fig. 6A, bath application of5-HT produced an inward current in the absence or presence of0.3 M TTX. Similar currents were observed in response tomCPBG (Fig. 6B). In layer I neurons, 40100 M 5-HT (10 of108) and 40100 M mCPBG (4 of 43 cells) induced a directinward current (315 319 pA, ranging from 30 to 1,000 pA)at a holding potential of70 mV (Fig. 6, A and B). In the

remainder of the layer I cells, 5-HT and mCPBG did not inducedetectable direct inward currents or changes in input resistance.On application of 5-HT or mCPBG to responding cells, theinward current developed rapidly. In the continued presence of5-HT or mCPBG, the current declined, presumably due todesensitization. The exact kinetics of both activation and de-sensitization were not examined because bath application ofdrugs was employed. In the responding cells, 5-HT induced adecrease in input resistance, ranging from 10 to 75% (Fig. 6, Aand B). The decrease in input resistance was correlated with the

magnitude of the inward current. The relatively large amplitude of the observed 5-HT

3-receptor-mediated current suggest

that the low number of responsive cells was due to a paucity of5-HT

3-receptor-expressing cells not a problem in current de

tection. Furthermore neither 5-HT nor mCPBG was able toinduce any direct inward current in the pyramidal neurontested (n 82).

The reversal potential of the 5-HT3

-receptor-mediatedcurrent was examined by voltage-ramp experiments. ACsCl-based intracellular pipette solution was used to par

tially block voltage-dependent K

currents in these experiments. Currents were evoked by ramping cells from 35 to65 mV in 10 ms in the absence and presence of 100 M5-HT. The difference current, obtained by subtracting thecontrol current from the current evoked in the presence o5-HT, represents the current induced by 5-HT. The currenreversed polarity between 5 and 2 mV in the three layeI cells tested (Fig. 7). An inward rectification was evident inthe current-voltage relation in the voltage range 65 to 35mV. A similar inward rectification of 5-HT

3-receptor-medi

FIG. 4. 5-HT and -methyl-5-HT induced a moderate enhancement of sIPSCs in layer I neurons. Recordings were madefrom a 17-day-old frontal layer I neuron at 70 mV. Bathingsolution contained 20 M D-APV and 10 M CNQX but noTTX. A: sIPSCs recorded under control condition. Mean interevent interval and amplitude during the control period were 190ms and 62 pA, respectively. B: bath application of 20 M-methyl-5-HT enhanced sIPSCs. Mean interevent interval wadecreased to 90 ms for the 2-min peak period. Mean amplitudewas only increased to 68 pA. C: enhancing effect of-methyl5-HT on sIPSCs started to decline in 5 min; sIPSCs declinedto control level in 10 min. D: scatter plot showing the enhancement of sIPSCs by -methyl-5-HT and the desensitization of this effect during the entire recording.

FIG. 5. Transient enhancement of sIPSCs by 5-HTreceptors. Recordings were made from a 17-day-olfrontal layer I neuron (top) and a 16-day-old frontapyramidal neuron (bottom) at 70 mV in the presencof 20 M D-APV and 10 M CNQX but no TTX. Inboth of these 2 neurons, bath application of 100 MmCPBG, a specific 5-HT3 agonist, evoked a brief bursof sIPSCs, lasting for 5 s.



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ated currents has been observed in other cell types (Kawa1994; Yang et al. 1992).

We also tested both mCPBG and -methyl-5-HT in 10

pyramidal neurons. In each of these cells, bath application of40 or 80 M mCPBG for 5 min failed to induce any visiblechange in sIPSCs, whereas subsequent application of 20 M-methyl-5-HT was able to induce a strong enhancement ofsIPSCs (Fig. 8). These results suggest that there are moreinterneurons expressing 5-HT

2Athan 5-HT

3receptor in cere-

bral cortex, as indicated by recent anatomic studies (Jakab andGoldman-Rakic 1998; Morales and Bloom 1997; Willins et al.1998).

5-HT enhances sEPSCs but not mEPSCs in pyramidal cells

It has been reported that 5-HT can increase pyramidal cellexcitability (Araneda and Andrade 1991; Sheldon and Agha-

janian 1991). Accordingly, we reasoned that 5-HT might in-duce an increase in sEPSCs. To test this idea, we recordedsEPSCs from pyramidal neurons after blockade of GABAergicinhibition with 10 M Bic. Bath application of 5-HT (50100M, n 7) or -methyl-5-HT (20 M, n 8) enhancedsEPSCs in each of these cells (Fig. 9). The mean frequency ofsEPSCs was increased to 880 230% of control levels. Mostof the increase in frequency was due to an augmentation in thenumber of small- and medium-amplitude events. The meanamplitude of sEPSCs was not or only minimally enhanced(20%). The 5-HT- and -methyl-5-HT-induced enhancementof sEPSC frequency also displayed desensitization. However,this process was slower than that observed with sIPSCs: thefrequency started to decline 10 min after applying 5-HT or-methyl-5-HT. Further, this desensitization was not complete.The frequency of sEPSCs was still higher in the prolongedpresence of 5-HT or -methyl-5-HT than that under controlconditions and was sustained as long as the recording conditionwas stable. Preincubation of brain slices with 10 M risperi-done prevented -methyl-5-HT from having any effect onsEPSCs in two pyramidal neurons from two slices, suggestingan involvement of 5-HT

2Areceptors.

In the presence of 0.3 M TTX, neither 5-HT nor -methyl-5-HT induced any change in mEPSCs (n 6). These resultssuggested that 5-HT and -methyl-5-HT might induce action

potential firing in pyramidal neurons. However, bath application of 5-HT or -methyl-5-HT did not induce any detectabledirect inward current in the absence (n 53) or presence (n

6) of TTX or depolarization (n 4) in pyramidal neuronsInput resistance of these pyramidal neurons was also nochanged by 5-HT or -methyl-5-HT.

5-HT did not enhance sEPSCs in layer I neurons

To further characterize the effects of 5-HT on cortical neuronal circuits, we studied the modulation of excitatory synapticinputs to layer I neurons, a type of cortical interneuron. Incontrast to pyramidal neurons, 5-HT (50 or 100 M, n 6and -methyl-5-HT (20 M, n 5) were unable to induce anydetectable change in the frequency or amplitude of sEPSCs(Fig. 10). Kinetics of these sEPSCs were also not altered by

5-HT or -methyl-5-HT and were similar to those reportedpreviously (Zhou and Hablitz 1997a).

FIG. 6. 5-HT and 1-(m-chlorophenyl)-biguanide (mCPBG) induced direct transient inward currents in a minority of layer I neuronsRecordings were made from a 17-day-oldfrontal layer I neuron at 70 mV in the presence of 20 M D-APV and 10 M CNQX buno TTX. A: bath application of 50 M 5-HTinduced a large direct inward current of550pA at peak. Current declined in the continuedpresence of 5-HT. Note that there was anincrease in sIPSCs on the declining phase othe direct inward current, indicating that therwas a slower 5-HT receptor mediating thdelayed enhancement of sIPSCs. B: after 30min of washing out 5-HT, bath application o50 M mCPBG induced a similar direct inward current of450 pA at peak in the samelayer I neuron. The smaller amplitude walikely a result of less optimal recording conditions. Current also showed a desensitizationin the continued presence of mCPBG. Notthat there was no increase in sIPSCs.

FIG. 7. Current-voltage relation for the 5-HT-induced current in a layer neuron. Control bathing solution contained 0.3 M TTX, 20 M D-APV, 10M CNQX, and 10 M bicuculline methiodide (Bic). Intracellular pipettsolution contained 135 mM CsCl. A, top: command voltage protocol used. Celwas held at 65 mV, stepped to 35 mV for 1 s to inactivate voltage-dependencurrents, and then ramped back to 65 mV. Middle and bottom: currentevoked by ramping the cell from 35 to 65 mV in the absence and presenceof 100 M 5-HT. B: difference current, obtained by subtracting the controcurrent from the current evoked in the presence of 5-HT, represents th5-HT-induced current. This current, when plotted against voltage changereverses its polarity near 0 mV and shows a modest inward rectification.



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5-HT decreased eIPSCs and eEPSCs in pyramidal neurons

In the nucleus accumbens, Nicola and Malenka (1997) re-ported that dopamine inhibited evoked IPSCs by depressingCa2 influx through voltage-dependent Ca2 channels. There-fore we reasoned that the enhancement of sIPSCs and sEPSCsinduced by 5-HT

2Areceptor activation might mediated by

increased Ca2 influx through voltage-dependent Ca2 chan-nels. To test this idea, we examined the effects of 5-HT onevoked IPSCs (eIPSCs) and eEPSCs in pyramidal neurons. Asshown in Fig. 11, monosynaptic eIPSCs were reliably evokedin the presence of 10 M CNQX and 40 M D-APV. A modestpaired-pulse synaptic depression was observed at intervals of100200 ms. Bath application of 40 M 5-HT induced arobust increase in sIPSCs each of the 5 pyramidal neuronstested (Fig. 11). However, 5-HT simultaneously decreased theamplitude of eIPSCs to 80% of control level in these cells.Paired-pulse depression was not significantly changed. Simi-larly, eEPSCs in pyramidal neurons were reduced, whereassEPSCs were enhanced in frequency (n 4 cells).

The strong enhancement of sIPSCs and sEPSCs induced by5-HT

2Areceptor activation does not appear to be mediated by

increased Ca2 influx. Instead, a decrease in eEPSCs andeIPSCs suggests that 5-HT might modulate the availability otransmitter vesicles (Wang and Zucker 1998). SimilarlyKondo and Marty (1998) reported that norepinephrine increased sIPSCs but decreased eIPSCs in cerebellar stellateneurons.

D I S C U S S I O N

The main findings of this study are that 5-HT induces alarge, desensitizing enhancement of sIPSCs and a weakelonger-lasting enhancement of sEPSCs through 5-HT

2Arecep

tors and that 5-HT3

receptors appear to be present exclusivelyon interneurons. These results may provide a cellular explanation to the predominantly inhibitory 5-HT effect in cerebracortex.


receptors induces a desensitizingenhancement of sIPSCs in pyramidal neurons

In the present study, carried out in a neocortical in vitro slicepreparation, the most prominent effect of 5-HT was a strong

FIG. 8. 5-HT2A receptor expressing interneurons are more abundant than 5-HT3 receptoexpressing interneurons. Recordings were madfrom an 18-day-old frontal pyramidal neuron a70 mV in the presence of 20 M D-APV and10 M CNQX but no TTX. A: sIPSCs recordedunder control condition. B: bath application o80 M mCPBG induced no visible change insIPSCs. C: bath application of 20 M -methyl5-HT, on top of 80 M mCPBG, induced massive enhancement of sIPSCs. D and E: scat

ter plots showing the effects of mCPBG an-methyl-5-HT on interevent interval and amplitude of sIPSCs during the entire recording.



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enhancement of sIPSCs in pyramidal neurons. This effectappeared to be mediated predominantly by 5-HT

2Areceptors

because it was mimicked by the 5-HT2-agonist -methyl-5-HT

and blocked by the specific 5-HT2A

-antagonist risperidone.This is consistent with the fact that 5-HT

2Areceptors are the

most abundant 5-HT receptors in the cerebral cortex (Burnet etal. 1995; Jakab and Goldman-Rakic 1998; Mengod et al. 1997;Willins et al. 1997; Wright et al. 1995). A similar action of5-HT

2Areceptors has been reported in the hippocampus

(Piguet and Galvan 1994; Shen and Andrade 1998). This 5-HTenhancement of sIPSCs fits well with the generally inhibitoryeffects of 5-HT repeatedly observed in cerebral cortex in vivo(Reader and Jasper 1984). However, Aghajanian and Marek(1997) recently reported that, in rat neocortical pyramidalneurons in vitro, 5-HT

2Areceptor activation induced only a

minimal enhancement of sIPSCs with a strong enhancement ofsEPSCs, indicating an excitatory 5-HT effect on cerebral cor-tex. The reason(s) for this discrepancy is unknown.

How 5-HT2A

receptor activation leads to an enhancement ofsIPSCs is not clear. The increase in both frequency and am-plitude of sIPSCs and its TTX sensitivity suggested an en-hanced excitability of inhibitory neurons. However, our so-

matic recordings failed to reveal a 5-HT2A

-receptor-mediateddirect inward current or depolarization. This is similar to thesituation with 5-HT-induced enhancement of sEPSCs (Aghajanian and Marek 1997; present study). However, we cannorule out the possibility that a subset of GABAergic neuronwere depolarized by 5-HT but might have evaded our detection, especially most of our interneurons were from layer I andlaminar differences may exist. Cox et al. (1998) recently reported that glutamate locally activates dendritic terminals andinduces dendritic transmitter release, which is not detected bysomatic recording in thalamic interneurons. 5-HT may act onaxon and/or dendritic terminals in a similar fashion. Furthermore, because we used relatively large recording pipettesintracellular factor(s) might be dialyzed such that certain 5-HTresponses including the 5-HT-induced depolarization (Aranedaand Andrade 1991) were washed out in the recorded cell(Yakel et al. 1988). On the other hand, we found that 5-HTdecreased the amplitude of eIPSCs, indicating that 5-HT didnot increase action potential-evoked Ca2 influx. Therefore iseems that 5-HT

2Areceptor activation may instead affect trans

mitter vesicles through other signaling pathways. This is consistent with studies showing that 5-HT

2Areceptor activation

FIG. 9. -Methyl-5-HT enhances sEPSCs in pyramidal neurons. Recordings weremade from an 18-day-old frontal pyramidaneuron at 70 mV in the presence of 10 MBic but no TTX. A: sEPSCs recorded undecontrol condition. Mean interevent intervaand amplitude during the control period were2.1 s and 24 pA, respectively. B: bath application of 20 M -methyl-5-HT decreasedthe mean interevent interval of sEPSCs to 80ms. Mean amplitude was only increased to29.2 pA. Enhancing effect of-methyl-5-HTon sEPSCs showed little decline. C: addition

of 20 M D-APV and 10 M CNQX blockedall synaptic events. D and E: scatter plots osEPSC interevent interval and amplitudduring the entire recording.



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increases intracellular Ca2 concentration by releasing Ca2

from intracellular stores in nonneuronal cell types (Hagberg etal. 1998; Ozaki et al. 1997; Saucier and Albert 1997) and that5-HT might increase the number of transmitter vesicles avail-able for release (Wang and Zucker 1998).

The mechanism(s) underlying the desensitization of5-HT

2A-receptor-mediated enhancement of sIPSCs was not

examined in this paper. However, studies in nonneuronal cellsystems have indicated that agonist-induced desensitizationwas associated with decreased numbers of 5-HT

2Areceptors

(Berry et al. 1996; Roth et al. 1995; Saucier and Albert 1997).Because our observed desensitization of 5-HT

2A-receptor-me-

diated enhancement of sIPSCs showed a time course compa-rable with the agonist-induced internalization of 5-HT

2Are-

ceptors in a cell line (Berry et al. 1996), a similar mechanismmight be operational in cortical interneurons. A tonic desensi-tization may exist in cerebral cortex due to the physiologicalrelease of 5-HT, which may underlie 5-HT supersensitivity ofcortical pyramidal neurons after 5-HT denervation (Ferron etal. 1982).

We also found that 5-HT enhancement of sIPSCs in layer Ineurons was much weaker than in pyramidal neurons, indicat-

ing that GABAergic neurons innervating interneurons versuspyramidal neurons are differentially modulated by 5-HT.Therefore our results that 5-HT can greatly increase GABAer-gic inhibitory inputs to pyramidal neurons are consistent withthe large body of in vivo studies showing that 5-HT inhibitspyramidal neurons.


receptors enhances sEPSC frequency inpyramidal neurons

5-HT and -methyl-5-HT greatly increased the frequencybut not the amplitude of sEPSCs in every pyramidal neuron

tested, as reported by Aghajanian and Marek (1997). This isconsistent with Jakab and Goldman-Rakic (1998) that 5-HT

2A

receptors are expressed uniformly in all cortical pyramidaneurons. The enhancing effect was TTX sensitive. In a largesample of pyramidal neurons, no detectable direct inwardcurrent or input conductance change was produced by 5-HT or-methyl-5-HT. 5-HT also decreased the amplitude of eEPSCs. This situation is quite similar to that of 5-HT-induced

enhancement of sIPSCs. Therefore the possibilities envisionedfor sIPSC enhancement are also applicable to sEPSCs.

Recent data have shown that 5-HT2A

receptors are highlyexpressed in cortical pyramidal neurons, the proximal apicadendrites in particular (Hamada et al. 1998; Jakab and Goldman-Rakic 1998; Roth et al. 1997). This suggests that dendrites, the major postsynaptic membrane, are the major site o5-HT action. However, the strong enhancement of sEPSCfrequency suggests that 5-HT was acting presynaptically. Thiapparent contradiction may be reconciled by the followingpossibilities. First, dendritic 5-HT

2Areceptors might induce a

local depolarization (Cox et al. 1998). Such local effects cancause either dendritic transmitter release or a release of retro-

grade messengers with subsequent effects on presynaptic axonterminals (Maletic-Savatic and Malinow 1998; Morishita et al1998). Second, 5-HT

2Areceptors have been detected in a

minority of axon terminals (Jakab and Goldman-Rakic 1998)and activation of these terminal 5-HT receptors may be responsible for the observed sEPSC enhancement.

5-HT does not affect sEPSCs in layer I neurons

5-HT and -methyl-5-HT had no effect on sEPSCs in layeI neurons. Even though sampling bias might have contributedto this observation, the fact that activation of 5-HT

2Areceptor

induced robust enhancement of sEPSCs in all pyramidal neu

rons tested suggests that this differential modulation of sEPSCsin the two cell types was real. 5-HT

2Areceptor expression i

high in pyramidal neuron proximal apical dendrites and low indistal parts (Jakab and Goldman-Rakic 1998; Willins et al1997). It is possible that activation of dendritic 5-HT

2Arecep

tors may induce dendritic transmitter release and/or release oretrograde messenger(s). Therefore a lack of proximity of layerI neurons (Zhou and Hablitz 1996b) to pyramidal proximaapical dendrites may lead to a lack of 5-HT effect on sEPSCsin layer I neurons.

FIG. 11. 5-HT decreased evoked IPSCs (eIPSCs) in pyramidal neuronsRecordings were made from a 16-day-old frontal pyramidal neuron at 70 mVin the presence of 10 M CNQX and 40 M D-APV. Left: monosynaptieIPSCs recorded under control condition. Paired stimuli (5 V 0.1 ms) werdelivered at 100-ms interval. sIPSCs were small and relatively infrequen

Right: bath application of 40 M 5-HT induced a large increase in sIPSCs bua small decrease (by 20% in amplitude) in eIPSCs. Paired-pulse depressionwas not significantly changed.

FIG. 10. -Methyl-5-HT had no effect on sEPSCs in layer I neurons.Recordings were made from an 18-day-old frontal layer I neuron at 70 mV

in the presence of 10 M Bic but no TTX. A: sEPSCs recorded under controlcondition. B: bath application of 20 M -methyl-5-HT induced no visiblechange in sEPSCs. Cand D: cumulative plots showing that the amplitude (P0.99) and interevent interval (P 0.2) distributions of sEPSCs are notdifferent under control and -methyl-5-HT.



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5-HT3

receptors were observed only in interneurons

Our present results show that 5-HT and mCPBG induced alarge desensitizing inward current in fast spiking interneurons.This current had a reversal potential near 0 mV and showed amodest inward rectification. The induction of this current wasaccompanied by a large increase in input conductance, indi-cating that 5-HT was opening ion channels. These biophysicaland pharmacological properties suggest that this inward current

was mediated by 5-HT3 receptors (Derkach et al. 1989; Jack-son and Yakel 1995; Kawa 1994; McMahon and Kauer 1997;Yang et al. 1992). Consistent with a recent immunohistochem-ical study (Morales and Bloom 1997), this 5-HT

3-receptor-

mediated current was recorded exclusively in a small numberof cortical interneurons. However, it is possible that our rela-tively slow drug application system might have caused a cer-tain amount of underestimation of 5-HT

3receptor expression

in cortical neurons.The functional significance of such a highly selective ex-

pression of 5-HT3

receptors remains to be established. How-ever, it appears certain that a short pulse of 5-HT released from5-HT nerve terminals can result in a transient excitation offast-spiking interneurons and a subsequent transient inhibitionof targets innervated by these interneurons. It will be importantto determine if GABAergic neurons receiving 5-HT baskets(Hornug and Celio 1992) express 5-HT

3receptors. If that is the

case, then 5-HT baskets are suited ideally to rapidly deliverlarge amounts of 5-HT to 5-HT

3receptors on these neurons.

Functional considerations

Our data clearly show that 5-HT2A

-receptor-mediated ef-fects are widespread in cerebral cortex. Because of the lowdensity of 5-HT terminals and synapses, our results also sug-gest that nerve terminal-released 5-HT may spread and act onnonsynaptic 5-HT receptors (Audet et al. 1989; Descarries and

Umbriaco 1995; Seguela et al. 1989). Further, our data indicatethat in cerebral cortex, the predominantly inhibitory effect of5-HT might be affected by multiple factors; i.e., precise spatialand temporal location and quantity of 5-HT released, the rateof 5-HT clearance, and the state of the 5-HT receptors. Asshown by Blier and De Montigny (1997), most antidepressantsincrease brain 5-HT levels, whereas our results suggest thatsuch treatments may alter the sensitivity of 5-HT receptors onGABAergic neurons and thereby the excitation-inhibition bal-ance in cortical neuronal circuitry. Therefore 5-HT modulationof GABAergic neurons may play an important role in thepathophysiology and treatment of major psychiatric disorders(Abi-Dargham et al. 1997).

In conclusion, our study demonstrated that 5-HT preferen-

tially induced a large desensitizing enhancement of sIPSCs incortical pyramidal neurons; 5-HT also induced a weaker butlonger-lasting enhancement of sEPSCs in pyramidal neurons.Therefore short 5-HT pulses may inhibit cortical circuitry,whereas prolonged 5-HT presence may result in excitation.

We thank A. Margolis for excellent technical help and Dr. Lori McMahonfor commenting on an early version of this paper.

This work was supported by National Institutes of Health grants to J. J.Hablitz and a Young Investigator Award from National Alliance for Researchon Schizophrenia and Depression to F.-M. Zhou.

Present address and address for reprint requests: F.-M. Zhou, Division of

Neuroscience, Baylor College of Medicine, One Baylor Plaza, Houston, TX77030.

Received 16 February 1999; accepted in final form 15 July 1999.

REFERENCES

ABI-DARGHAM, A., LARUELLE, M., AGHAJANIAN, G. K., CHARNEY, D., ANDKRYSTAL, J. The role of serotonin in the pathophysiology and treatment oschizophrenia. J. Neuropsychiatry Clin. Neurosci. 9: 117, 1997.

AGHAJANIAN, G. K. AND MAREK, G. J. Serotonin induces excitatory postsyn

aptic potentials in apical dendrities of neocortical pyramidal neurons. Neuropharmacology 36: 589599, 1997.

ARANEDA, R. AND ANDRADE, R. 5-Hydroxytryptamine2 and 5-hydroxytryptamine1A receptors mediate opposing responses on membrane excitability in rat association cortex. Neuroscience 40: 399412, 1991.

AUDET, M. A., DESCARRIES, L., AND DOUCET, G. Quantified regional andlaminar distribution of the serotonin innervation in the anterior half of theadult rat cerebral cortex. J. Chem. Neuroanat. 2: 2944, 1989.

BAUMGARTEN, H. G. AND GROZDANOVIC, Z. Anatomy of the central serotoninergic projection systems. In: Serotoninergic Neurons and 5-HT Receptors inthe CNS, edited by H. G. Baumgarten and M. Gothert. Berlin, GermanySpringer-Verlag, 1997, p. 4189.

BAXTER, G., KENNETT, G., BLANEY, F., AND BLACKBURN, T. 5-HT2 receptosubtypes: a family re-united? Trends Pharmacol. Sci. 16: 105110, 1995.

BERRY, S., SHAH, M. C., KAHAN, N., AND ROTH, B. L. Rapid agonist-inducedinternalization of the 5-hydroxytryptamine2A receptor occurs via the endosome pathway in vitro. Mol. Pharmacol. 50: 306313, 1996.

BLIER, P. AND DE MONTIGNY, C. Current psychiatric uses of drugs acting on theserotonin system. In: Serotoninergic Neurons and 5-HT Receptors in theCNS, edited by H. G. Baumgarten and M. Gothert. Berlin, GermanySpringer-Verlag, 1997, P. 728749.

BURNET, P.W.J., EASTWOOD, S. L., LACEY, K., AND HARRISON, P. J. Thdistribution of 5-HT1A and 5-HT2A receptor mRNA in human brain. Brai

Res. 676: 157168, 1995.COX, C. L., ZHOU, Q., AND SHERMAN, S. M. Glutamate locally activate

dendritic outputs of thalamic interneurons. Nature 394: 478482, 1998.DAHLSTROM, A. AND FUXE, K. Evidence for the existence of monoamine

containing neurons in the central nervous system. I. Demonstration omonoamines in the cell bodies of brain stem neurons. Acta Physiol. ScandSuppl. 232: 155, 1964.

DAVIES, M. F., DEISZ, R. A., PRINCE, D. A., AND PEROUTKA, S. J. Two distinceffects of 5-hydroxytryptamine on single cortical neurons. Brain Res. 423347352, 1987.

DEFELIPE, J., HENDRY, S.H.C., HASHIKAWA, T., AND JONES, E. G. Synaptirelationships of serotonin-immunoreactive terminal baskets on GABA neurons in the cat auditory cortex. Cereb. Cortex 1: 177183, 1991.

DERKACH, V., SURPRENANT, A., AND NORTH, R. A. 5-HT3 receptors are membrane ion channels. Nature 339: 706709, 1989.

DESCARRIES, L. AND UMBRIACO, D. Ultrastructural basis of monoamine andacetycholine function in CNS. Semin. Neurosci. 7: 309318, 1995.

FERRON, A., DESCARRIES, L., AND READER, T. A. Altered neuronal responsiveness to biogenic amines in rat cerebral cortex after serotonin denervation odepletion. Brain Res. 231: 93108, 1982.

GABBOTT, P.L.A. AND SOMOGYI, P. Quantitative distribution of GABA-immunoreactive neurons in the visual cortex (area 17) of the cat. Exp. Brain Res61: 323331, 1986.

HAGBERG, G. B., BLOMSTRAND, F., NILSSON, M., TAMIR, H., AND HANSSON, EStimulation of 5-HT2A receptors on astrocytes in primary culture openvoltage-independent Ca2 channels. Neurochem. Intl. 32: 153162, 1998.

HAMADA, S., SENZAKI, K., HAMAGUCHI, K., TABUCHI, K., YAMAMOTO, H.

YAMAMOTO, T., YOSHIKAWA, S., OKANO, H., AND OKADO, N. Localization o5-HT2A receptor in rat cerebral cortex and olfactory system revealed byimmunohistochemitry using two antibodies raised in rat and chicken. Mol

Brain Res. 54: 199211, 1998.HORNUG, J. P. AND CELIO, M. R. The selective innervation by serotoninergi

axons of calbindin-containing interneurons in the neocortex and hippocampus of the marmoset. J. Comp. Neurol. 320: 457467, 1992.

HORNUG, J. P., FRITSCHY, J. M., AND TORK, I. Distribution of two morphologically distinct subsets of serotonergic axons in the cerebral cortex of themarmoset. J. Comp. Neurol. 297: 165181, 1990.

HOYER, D., CLARKE, D. E., FOZARD, J. R., HARTIG, P. R., MARTIN, G. R.MYLECHARANE, E. J., SAXENA, P. R., AND HUMPHREY, P.P.A. Internationaunion of pharmacology classification of receptors for 5-hydroxytryptamine(serotonin). Pharmacol. Rev. 46: 157203, 1994.



12/12

JACKSON, M. B. AND YAKEL, J. L. The 5-HT3 receptor channel. Annu. Rev.

Physiol. 57: 44768, 1995.JACOBS, B. L. AND AZMITIA, E. C. Structure and fuction of the brain serotonin

system. Physiol. Rev. 72: 165229, 1992.JAKAB, R. L. AND GOLDMAN-RAKIC, P. S. 5-Hydroxytryptamine2A serotonin

receptors in the primate cerebral cortex: possible site of action of halluci-nogenic and antipsychotic drugs in pyramidal cell apical dendrites. Proc.

Natl. Acad. Sci. USA 95: 735740, 1998.KAWA, K. Distribution and functional properties of 5-HT3 receptors om the rat

hippocampal dentate gyrus: a patch-clamp study. J. Neurophysiol. 71:19361947, 1994.

KONDO, S. AND MARTY, A. Differential effects of noradrenaline on evoked,spontaneous and miniature IPSCs in rat cerebellar stellate cells. J. Physiol.(Lond.) 509: 23343, 1998.

LIDOV, H.G.W., GRZANNA, R., AND MOLLIVER, M. E. The serotonin innervationof the cerebral cortex in the rat-an immunohistochemical analysis. Neuro-science 5: 207227, 1980.

MALETIC-SAVATIC, M. AND MALINOW, R. Calcium-evoked dendritic exocytosisin cultured hippocampal neurons. I. Trans-Golgi network-derived organellesundergo regulated exocytosis. J. Neurosci. 18: 68036813, 1998.

MARICQ, A. V., PETERSON, A. S., BRAKE, A. J., MYERS, R. M., AND JULIUS, D.Primary structure and functional expression of the 5-HT3 receptor, a sero-tonin gated ion channel. Science 254: 432437, 1991.

MENGOD, G., PALACIOS, J. M., WIEDERHOLD, K. H., AND HOYER, D. 5-Hy-droxytryptamine receptor histochemistry: comparison of receptor mRNAdistribution and radioligand autoradiography in the brain. In: Serotoninergic

Neurons and 5-HT Receptors in the CNS, edited by H. G. Baumgarten and

M. Gothert. Berlin, Germany: Springer-Verlag, 1997, p. 213237.MCMAHON, L. L. AND KAUER, J. A. Hippocampal interneurons are excitatedvia serotonin-gated ion channels. J. Neurophysiol. 78: 24932502, 1997.

MORALES, M. AND BLOOM, F. E. The 5-HT3 receptor is present in differentsubpopulations of GABAergic neurons in the rat telencephalon. J. Neurosci.17: 31573167, 1997.

MORISHITA, W., KIROV, S. A., AND ALGER, B. E. Evidence for metabotropicglutamate receptor activation in the induction of depolarization-inducedsuppression of inhibition in hippocampal CA1. J. Neurosci. 18: 48704882,1998.

MULLIGAN, K. A. AND TORK, I. Serotoninergic innervation of the cat cerebralcortex. J. Comp. Neurol. 270: 86110, 1988.

NICOLA, S. M. AND MALENKA, R. C. Dopamine depresses excitatory andinhibitory synaptic transmission by distinct mechanisms in the nucleusaccumbens. J. Neurosci. 17: 56975710, 1997.

OZAKI, N., MANJI, H., LUBIERMAN, V., LU, S. J., LAPPALAINEN, J., ROSENTHAL,N. E., AND GOLDMAN, D. A naturally occurring amino acid substitution of

the human serotonin 5-HT2A receptor influences amplitude and timing ofintracellular calcium mobilization. J. Neurochem. 68: 21862193, 1997.

PAXINOS, G. AND WATSON, C. The Rat Brain in Stereotaxic Coordinates (2nded.). Sydney: Academic, 1986.

PHILLIS, J. W. Microiontophoretic studies of cortical biogenic amines. In:Monoamine Innervation of Cerebral Cortex, edited by L. Descarries, T. R.Reader, and H. H. Jasper. New York: Alan R. Liss, 1984, p. 175194.

PIGUET, P. AND GALVAN, M. Transient and long-lasting actions of 5-HT on ratdentate gyrus neurons in vitro. J. Physiol. (Lond.) 481: 629639, 1994.

READER, T. A. AND JASPER, H. H. Interactions between monoamines and othertransmitters in cerebral cortex. In: Monoamine Innervation of CerebralCortex, edited by L. Descarries, T. R. Reader, and H. H. Jasper. New York:Alan R. Liss, 1984, p. 195225.

ROTH, B. L., PALVIMAKI, E. P., BERRY, S., KAHAN, N., SACHS, N., ULER, A.AND CHOUDHARY, M. S. 5-Hydroxytryptamine2A (5-HT2A) receptor desensitization can occur without down-regulation. J. Pharmacol. Exp. Ther. 27516381646, 1995.

SAUCIER, C. AND ALBERT, P. R. Identification of an endogenou5-hydroxytryptamine2A receptor in NIH-3T3 cells: agonist-induced downregulation involves decreases in receptor RNA and number. J. Neurochem

68: 19982011, 1997.SEGUELA, P., WATKINS, K. C., AND DESCARRIES, L. Ultrastructural relationship

of serotonin axon terminals in the cerebral cortex of the adult rat. J. Comp

Neurol. 289: 129142, 1989.SHELDON, P. W. AND AGHAJANIAN, G. K. Serotonin (5-HT) induces IPSCs in

pyramidal layer cells of rat piriform cortex: evidence for mediation by5-HT2-activated interneuron. Brain Res. 506: 6269, 1990.

SHELDON, P. W. AND AGHAJANIAN, G. K. Excitatory resposes to serotoni(5-HT) in neurons in rat piriform cortex: evidence for mediation by 5-HT1in pyramidal cells and 5-HT2 receptors in interneurons. Synapse 9: 2082181991.

SHEN, R . Y. AND ANDRADE, R. 5-Hydroxytryptamine2

receptor facilitate

GABAergic neurotransmission in rat hippocampus. J. Pharmacol Exp. Ther

285: 805812, 1998.SMILEY, J. F. AND GOLDMAN-RAKIC, P. S. Serotonergic axons in monke

prefrontal cerebral cortex synapse predominantly on interneurons as demonstrated by serial section electron microscopy. J. Comp. Neurol. 367431443, 1996.

TANAKA, E. AND NORTH, R. A. Actions of 5-hydroxytryptamine on neurons o

the rat cingulate cortex. J. Neurophysiol. 69: 174957, 1993.TORK, I. Anatomy of the srotonergic system. Ann. NY Acad. Sci. 600: 935

1990.WANG, C. AND ZUCKER, R. S. Regulation of synaptic vesicle recycling by

calcium and serotonin. Neuron 21: 155167, 1998.WILLINS, D. L., DEUTCH, A. Y., AND ROTH, B. L. Serotonin 5-HT2A receptor

are expressed on pyramidal neurons and interneurons in the rat cortexSynapse 27: 79 82, 1997.

WRIGHT, D. F., SEROOGY, K. B., LUNDGREN, K. H., DAVIS, B. M., AND JENNESL. Comparative localization of serotonin1A, 1C, and 2 receptor subtypmRNAs in rat brain. J. Comp. Neurol. 351: 357373, 1995.

YAKEL, J. L., TRUSSELL, L. O., AND JACKSON, M. B. Three serotonin response

in cultured mouse hippocampal and striatal neurons. J. Neurosci. 8: 12751285, 1988.

YANG, J., MATHIE, A., AND HILLE, B. 5-HT3 receptor channels in dissociated rasuperior cervical ganglion neurons. J. Physiol. (Lond.) 448: 237256, 1992

ZHOU, F.-M. AND HABLITZ, J. J. Rat neocortical layer I neurons. I. Actionpotential and repetitive firing properties. J. Neurophysiol. 76: 6516671996a.

ZHOU, F.-M. AND HABLITZ, J. J. Morphological properties of intracellularlylabeled rat neocortical layer I neurons. J. Comp. Neurol. 376: 1982131996b.

ZHOU, F.-M., HABLITZ, J. J. Rapid kinetics and inward rectification of miniature EPSCs in layer I neurons of rat neocortex. J. Neurophysiol. 7724162426, 1997a.

ZHOU, F.-M. AND HABLITZ, J. J. Metabotropic glutamate receptor enhancemenof spontaneous IPSCs in neocortical interneurons. J. Neurophysiol. 7822872295, 1997b.


fu-ming zhou and john j. hablitz- activation of serotonin receptors modulates synaptic transmission...

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