Animal Models of SchizophreniaPharmacological Models- Advantages and Challenges -
Thomas Steckler
Pharmacological Models
• Does the model impair cognitive function in domains relevant to SZ?• Does the model resemble some of the pathophysiological constructs thought to contribute to
SZ?• Do we see relevant effects of therapeutic intervention in the model? • Can the effects seen in the model be reproduced (within/across labs) and is the model reliable?
Dopamine Glutamate CB 5-HT
Test
Acute(Sub-)chronic/Sensitization Withdrawal/Abstinence Neurodevelopmental (pre-/postnatal)
Manipulation
Measure
Publications on Pharmacological Models of Schizophrenia 2009
Medline search• 584 hits• 94 articles selected• 125 models published
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Challenge Models – General Features• In general based on face validity
– Drugs like amphetamine, lysergic acid diethylamide (LSD), phencyclidine (PCP), or ketamine produce schizophrenia-like symptoms in humans and/or exacerbate symptoms in schizophrenic patients
– Used to mimic aspects of schizophrenia in animals, almost exclusively originate from attempts to model positive symptoms
• High degree of practicability– Flexibility in choice of test, not limited to species-specific model (construct validity)– Allow for high throughput (esp. acute challenge models)– Duration of test rather than model generation may become the time-critical step
• Good validity to predict efficacy of antipsychotics to treat positive symptoms– Effective screening tools
Challenge Models – General Features
• In general, reports of activity in a wide variety of preclinical tests relevant for cognitive domains affected in schizophrenia– Speed of processing, attention, working memory, visual learning and
memory, problem solving/executive control, social cognition, gating• Good sensitivity to established and novel mechanisms of
action, also in tests of cognition– E.g., atypical antipsychotics, D1, 5-HT6, AMPA, mGlu2/3, mGlu5,
PDE10, nic. α7,…– Sensitivity depends on response window, which varies as a function of
model and test• Small window may lead to difficulties in detecting effects of test compounds
Challenge Models – General Features
dose
unreliable toxicnon-specificdesired irreversibility
PCP• NMDA channel blocker• Sigma receptor• Other ion channel receptors• Transporters• GPCRs
• Allow for fine-tuning of the models according to the need– Dose-response and time-response pilot studies help to optimize the
model for the specific test condition and to the compounds under investigation
– High variability in methodological details across labs, also in seemingly similar models
• Dose, route of administration, time of administration, duration and treatment regime in case of repeated dosing
– Different dosing risks undesired effects (esp. in acute and chronic models)
Challenge Models – General Features• Effects of challenge may depend on exact compound employed
– Seemingly the same mechanism of action may result into differed behavioural profile
• NMDA antagonists tested in various VI schedules of reinforcement
• Biconditional VI 30/VI 30:– Two-lever operant chamber– CS presentation: rats were rewarded under VI 30
schedule at the appropriate lever conditional on the presentation of a conditional stimulus (clicks or light)
– ISI: No stimuli presented, both levers present but inactive
• PCP decreased lever press rate and response accuracy at highest dose during CS presentation
• MK-801 had biphasic effects• Ketamine and memantine decreased
responding
Effects of NMDA antagonists on biconditional VI30/VI30
Gilmour et al., Psychopharmacology 205, 2009
Acute Challenge Models – Advantages and Disadvantages
• Good cross-species neural homology– From invertebrate to man, translational model– Some notable exceptions, e.g. PCP (neurotoxicity, abuse liability prevent
human testing)
Acute ketamine increases RCGU in HV
Frontomedial cortexFrontolateral cortexAnterior cingulate cortexPosterior cingulate cortexParietal cortexSomatosensory cortexMotor cortexTemporlateral cortexTemporomedial cortexOccipitomedial cortexOccipitolateral cortexCaudate nucleusPutamenThalamusCerebellum
Vollenweider et al., Eur Neuropsychopharmacology 7, 1997
Ketamine 30 mg/kg IP MK-801 0.5 mg/kg IP
Saline IP
Miyamoto et al., Neuropsychopharmacology 22, 2000
NMDA antagonism increases 2-DG brain uptake in mice
Acute Challenge Models – Advantages and Disadvantages
• Allow for deconstruction of the cognitive processes involved– E.g., effects on acquisition vs. consolidation vs. retrieval vs. extinction– No risk of carry-over effects
• Allow for deconstruction of the neural processes involved– E.g., local infusions into selected brain areas
• May represent mechanistic rather than disease models
Hertel et al., Behav Brain Res 72, 1995
1.5 mg/kg s.c.
2.5 mg/kg s.c.
Abi-Dargham and Moore, Neuroscientist 9, 2003
Increased prefrontal dopamine release following acute amphetamine in rats
Cognitive symptoms in schizophrenia associated with
prefrontal DA hypofunction
Acute Challenge Models – Advantages and Disadvantages
• Gained popularity due to high sensitivity to detect clinically used drugs– Risks to detect more of the same
• Potential drug/drug interactions• Time-dependent effects
– Pharmacokinetics determine behavioural response• Need for time-limited cognitive tests
– Pharmacodynamics may determine behavioural response
Prefrontal Dopamine Prefrontal Glutamate
PCP-induced DA peak followed by sustained glutamate efflux
Adams and Moghaddam, J Neurosci 15, 1998
PCP increases peripheral and central AMPH levels
Sershen et al., Neurochem Int 52, 2008
Acute AmphetamineEffects on Cognitive Function in Animals
Reduced 5-CSRRT reaction time / increased impulsivity in rats
Higgins et al., Behav Brain Res 185, 2007
Impaired conditional discrimination in rats
Dunn et al., Psychopharmacology 177, 2005
Reduced stop-signal reaction time in rats with slow baseline
Feola et al., Behav Neurosci 114, 2000 Idris et al., Psychopharmacology 179, 2005
Impaired reversal learning in rats
Amphetamine Effects Aren’t Necessarily Disruptive, but Depend on Task DifficultyIncreasing attentional load improves accuracy and shortens correct response
latency in rats on 5-CSRRT
Grottick and Higgins, Psychopharmacology 164, 2002
total trials total trials
• Extended number of trials (100 → 250), beneficial effects seen during later stages• Shorter stimulus duration (0.5 s → 0.25 s)
Antipsychotics Reverse Effects of Acute Amphetamine
Haloperidol, but not clozapine, reverses the amphetamine-induced impairment in reversal learning
Idris et al., Psychopharmacology 179, 2005
Clozapine, but not haloperidol or eticlopride, reverses the amphetamine-induced impairment in conditional
discrimination
Dunn and Killcross, Psychopharmacology 188, 2006
• Validity to predict cognitive enhancing effects in patients limited ?
Acute PCP – Impairments Across Multiple Cognitive Domains
Speed of processing, attention
Social cognition
Working memory
Visual learning and memory
Problem solving, flexibility
Antipsychotics Reverse Effects of Acute PCP
Task Species Attenuation of PCP Deficit Reference5-CSRTT Rat • Clozapine (acute)
• Clozapine (chronic)• Risperidone
ExacerbatesNOExacerbates
Amitai et al., Psychopharmacology 193, 2007
Reversal learning Rat • Clozapine• Lamotrigine
YESYES
Idris et al., Psychopharmacology 179, 2005
Radial arm maze Rat • Quetiapine (chronic) YES He et al., Behav Brain Res 168, 2006
Social recognition Rat • Clozapine• Amisulpride• Haloperidol
YES (partially)YESNO
Terranova et al., Psychopharmacology 181, 2005
• Acute PCP model seems more sensitive to atypical than to typical antipsychotics
• Limited validity to predict cognitive enhancing effects in patients ?
Attenuation of PCP effects on prefrontal rCBF
Gozzi et al., Neuropsychopharmacology 33, 2008
Repeated Challenge Models
• Suggested to better model the behavioural and metabolic dysfunction of schizophrenia
• Translational value: comparison with e.g. amphetamine, PCP or ketamine abusers (etiological validity)
• (Sub-)chronic models allow for testing at steady state (osmotic minipump)
• Abstinence models– Enable testing without challenge drug on board– Reduce some pharmacokinetic issues (e.g., drug/drug interactions,
dependency on T½)– At least in part based on finding that dug-induced psychosis can last
for weeks despite abstinence (e.g. PCP)
Effects of Amphetamine Abstinence in Man
• The effects of repeated exposure to amphetamine reproduce the main features of paranoid schizophrenia, cognitive and negative symptoms
• Following discontinuation of drug use, subjects remain more sensitive to the psychotogenic effects of amphetamine
• There is an increased sensitivity of the mesolimbic dopamine system to the effects of amphetamine, which resembles the hyper-responsiveness seen in the system in schizophrenic patients
Reviewed in Sarter et al., Psychopharmacology 202, 2009
Index Brain area Effect ReferenceDopamine Prefrontal cortex - basal utilization Hamamura and Fibiger, Eur J Pharmacol 237, 1993
↑ stress-induced utilizationGABA Prefrontal cortex ↓ parvalbumin immunoreactivity Morshedi and Meredith, Neuroscience 149, 2007
Glucose utilization Accumbens ↓ basal utilization Tsai et al., Psychiat Res 57, 1995
NGF Hippocampus, occ cortex, hypothals
↓ level Angelucci et al., Eur Neuropsychopharmacol 17, 2007
BDNF Occipital cortex, hypothalamus
↓ level Angelucci et al., Eur Neuropsychopharmacol 17, 2007
CaMKII Striatum ↑ expression Greenstein et al., Synapse 61, 2007
Repeated Amphetamine – Neurobiological Effects in Rodents
Effects of Amphetamine Sensitization, Withdrawal and Abstinence
Naive
Sensitized
Hedou et al., Neuropharmacology 40, 2001
Amphetamine 1.5 mg/kg IP 5 days
Withdrawal 2 days, followed by microdialysis
Fletcher et al., Neuropsychopharmacology 32, 2007
sensitization weeks withdrawal weeks
Altered prefrontal DA levels in sensitized animals under withdrawal
Long-lasting 5-CSRTT deficit
Amphetamine 1 - 5 mg/kg 3x/week, 5 weeks
Attenuation of Impaired Performance in Amphetamine Abstinent Rats by D1 Agonism
Increased impairment with increased attentional load
Testing during weeks 6 + 7 of withdrawal
Stimulation of prefrontal D1 with SKF38393 improves performance in sensitized rats
SKF 0.06 µg
Testing during weeks11 + 12 of withdrawal
Fletcher et al., Neuropsychopharmacology 32, 2007
Cognitive Effects of Amphetamine Sensitization
Sarter et al., Psychopharmacology 202, 2009
Antipsychotics Attenuate the Effects of Amphetamine Pre-treatment
Pre-treatment regimen
Attenuation of impaired attention by haloperidol and clozapine
VI: Vigilance IndexHaloperidol 0.025 mg/kg SC, 10 daysClozapine 2.5 mg/kg SC, 10 daysAll rats received amphetamine (1.0 mg/kg) challenge
Sustained attention task
Martinez and Sarter, Neuropsychopharmacology 33, 2008
Effects of Subchronic PCP on DA Utilization and Metabolic Activity
Subchronic PCP reduces basal DA utilization in prefrontal cortex in rats
Jentsch et al., Neuropsychopharmacology 17, 1997
Subchronic PCP reduces LCGU in prefrontal cortex in rats
Vehicle
PCP (2.58 mg/kg chronic intermittend)
Cochran et al., Neuropsychopharmacology 28, 2003
PCP Abstinence – Neurochemical and Neuroanatomical Effects Suggest Decent Etiological
Validity vis-a-vis Schizophrenic PatientsIndex Brain area Effect Reference
Dopamine Prefrontal cortex ↓ basal utilization Jetsch et al., Science 277, 1997
↓ stress-induced utilization Jentsch et al., Neuropsychopharmacology 17, 1997; Noda et al., Neuropsychopharmacology 23, 2000
Glutamate Prefrontal cortex ↓ extracellular basal level Murai et al., Behav Brain Res 180, 2007
GABA Frontal cortex, hippocampus
↓ parvalbumin expression Cochran et al., Neuropsychopharmacology 28, 2003; Reynolds et al., Neurotox Res 6, 2004; Abdul-Monim et al., Behav Brain Res 169, 2006
Glucose utilization Prefrontal cortex ↓ basal utilization Cochran et al., Neuropsychopharmacology 28, 2003*
NAA and NAAG Temporal cortex ↓ level Reynolds et al., Schizophr Res 73, 2005
CaMKII Prefrontal cortex ↓ learning-associated phosphorylation
Enomoto et al., Mol Pharmacol 68, 2005
↓ swim-stress-induced phosphorylation
Murai et al., Behav Brain Res 180, 2007
ERK Hippocampus, amygdala ↓ learning-associated phosphorylation
Enomoto et al., Mol Pharmacol 68, 2005
Neurodegeneration Cingulate cortex Neuronal vacuolization Olney et al., Science 244, 1989
Cingulate, entorhinal, retrospl cx, hippocampus
Altered morphology Ellison and Switzer, Neuroreport 5, 1993
Prefrontal cortex ↓ number of spine synapses↑ astroglial process density
Hajszan et al., Biol Psychiatry 60, 2006
Modified from Mouri et al., Neurochem Int 51, 2007*chronic intermittent
Cognitive Effects Acute versus Chronic PCP
• High degree of heterogeneity of treatment regimes (number, frequency, duration, dose)
• Testing w/o PCP challenge dose
Acute PCP Chronic PCP Comment5-CSRRT Mild impairment (Amitai et al.,
Psychopharmacology 193, 2007)Impairment (Amitai et al., Psychopharmacology 193, 2007; Amitai & Markou, Psychopharmacology 202, 2009)
Tested over 5 days repeated treatment
Set shifting Impairment (Eggerton et al., Psychopharmacology 179, 2005)
No impairment (Deschenes et al., Behav Brain Res 167, 2006)
Test 1 day after 33 days treatment
Novel object recognition
Novelty preference intact (Pichat et al., Neuropsychopharmacology 32, 2007)
Impairment (Mandillo et al., Behav Pharmacol 14, 2003)
Test 1 day after 5 days treatment
Delayed alternation
Delay-dep. impairment (Jentsch et al., Neuropsychopharmacology 17, 1997)
Water maze Impaired acquisition (Podhorna & Didriksen, Behav Pharmacol 16, 2005; Wass et al., Behav Brain Res 174, 2006)
Impaired acquisition, intact consolidation (Didriksen et al., Psychopharmacology 193, 2007; Podhorna & Didriksen, Behav Pharmacol 16, 2005))
Cognitive Effects Acute versus Abstinence from Chronic PCP
Acute Wihdrawal/AbstinenceSet shifting ↓ ED shift (Eggerton et al.,
Psychopharmacology 179, 2005)↓ ED shift (Rodefer et al., Eur J Neurosci 21, 2005; McLean et al., Behav Brain Res 189, 2008; Goetghebeur and Dias, Psychopharmacology 202, 2009; Broberg et al., Psychopharmacology 206, 2009)
- (Fletcher et al., Psychopharmacology 183, 2005)
Reversal learning ↓ (Idris et al., Psychopharmacology 179, 2005)
↓ (Abdul-Monim et al., J Psychopharmacol 21, 2006; Abdul-Monim et al., Behav Brain Res 169, 2006)
Novel object recognition
- Novelty preference (Pichat et al., Neuropsychopharmacology 32, 2007)
↓ Novelty preference (Hashimoto et al., Eur J Pharmacol 519, 2005; Harte et al., Behav Brain Res 184, 2007; Nagai et al., Psychopharmacology 202, 2009)
↓ Novelty preference following additional acute PCP challenge (Pichat et al., Neuropsychopharmacology 32, 2007)
Delayed alternation, T-maze
↓(Stefani and Moghaddam, Behav Brain Res 134, 2002)
↓ Delay-dependent (Seillier and Giuffrida, Behav Brain Res 204, 2009)
- (Stefani and Moghaddam, Behav Brain Res 134, 2002)
Reference memory, radial maze
- (Li et al., Pharmacol Biochem Behav 75, 2003)
Antipsychotics Reverse Effects of Repeated PCPTask Species Attenuation of PCP deficit Reference5-CSRTT Rat • Clozapine (chronic) YES Amitai et al., Psychopharmacology 193, 2007
Set shifting Rat • Clozapine• Risperidone• Haloperidol
YESYESNO
McLean et al., Behav Brain Res 189, 2008
• Sertindole• Risperidone• Haloperidol• (Modafinil)
YESNONOYES
Goetgebheur and Dias, Psychopharmacology 202, 2009
• Sertindole YES Broberg et al., Psychopharmacology 206, 2009
Object retrieval Monkey • Clozapine (3 days) YES Jentsch et al., Science 277, 1997
Novel object recognition
Rat • Clozapine• Risperidone• Haloperidol
YESYESNO
Grayson et al., Behav Brain Res 187, 2007
Mouse • Clozapine• Haloperidol
YESNO
Hashimoto et al., Eur J Pharmacol 519, 2005
• Aripiprazole• Haloperidol
YESNO
Nagai et al., Psychopharmacology 202, 2009
Water maze Rat • Clozapine• Risperidone• Sertindole• Haloperidol
YESYESYESNO
Didiriksen et al., Psychopharmacology 193, 2007
• Data support suggestion that repeated PCP model is more sensitive to atypical than to typical antipsychotics – but limited use of typical antipsychotics
Conclusion IAcute DA and NMDA Challenge Models
• Generally considered to be of predictive utility for models of positive symptoms
• High degree of cross-species neural homology – Comparable biological substrates affected across species
• Translational model: can be used to challenge healthy volunteers under well controlled experimental conditions
• Limited utility as disease model of cognitive symptoms• Limited etiological validity vis-a-vis schizophrenia
• Useful for screening purposes, to increase the response window (testing of impaired rather than normal animals)
• Strong mechanistic aspect, risks detection of compounds with effects analogous to current antipsychotics and false positives; no reports of superiority of novel mechanisms of action
Conclusion IIRepeated DA and NMDA Challenge Models• Activity in a wide variety of preclinical test relevant for cognitive domains
impaired in schizophrenia• High degree of cross-species homology/etiological validity
– Comparable biological substrates affected across species– Neurochemical and –anatomical features resembling schizophrenia more closely
• Translational model: can be used to compare with certain non-schizophrenic human populations (e.g., amphetamine abusers) to bridge the gap
• Highly variable treatment and test protocols– Difficulty to compare results across labs and to evaluate reliability and
reproducibility
• Atypical antipsychotics more efficacious than typical antipsychotics • Some novel mechanisms of action show activity – but definitive clinical
proof of concept missing
Flipping the Coin
• Do effects of atypical antipsychotics in pharmacological models of schizophrenia translate into effects on cognitive function in schizophrenic patients?
• Are these clinical effects statistically significant or clinically relevant?
• Answer determines utility of pharmacological models to predict therapeutic effects