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