The DBA/2J strain and prepulse inhibition of startle: a model system to test antipsychotics?

Ketogenic diet for schizophrenia: clinical implication

PURPOSE OF REVIEW

The aim of this article is to review recent findings on the efficacy of ketogenic diet in preclinical models and in patients with schizophrenia. This review will also highlight emerging evidence for compromised glucose and energy metabolism in schizophrenia, which provides a strong rationale and a potential mechanism of action for ketogenic diet.

RECENT FINDINGS

Recent transcriptomic, proteomic and metabolomic evidence from postmortem prefrontal cortical samples and in-vivo NMR spectroscopy results support the hypothesis that there is a bioenergetics dysfunction characterized by abnormal glucose handling and mitochondrial dysfunctions resulting in impaired synaptic communication in the brain of people with schizophrenia. Ketogenic diet, which provides alternative fuel to glucose for bioenergetic processes in the brain, normalizes schizophrenia-like behaviours in translationally relevant pharmacological and genetic mouse models. Furthermore, recent case studies demonstrate that ketogenic diet produces improvement in psychiatric symptoms as well as metabolic dysfunctions and body composition in patients with schizophrenia.

SUMMARY

These results support that ketogenic diet may present a novel therapeutic approach through restoring brain energy metabolism in schizophrenia. Randomized controlled clinical trials are needed to further show the efficacy of ketogenic diet as a co-treatment to manage both clinical symptoms and metabolic abnormalities inherent to the disease and resulted by antipsychotic treatment.

Ketogenic diet prevents impaired prepulse inhibition of startle in an acute NMDA receptor hypofunction model of schizophrenia

Recent transcriptomic, proteomic and metabolomics studies have highlighted an abnormal cerebral glucose and energy metabolism as one of the potential pathophysiological mechanisms of schizophrenia. This raises the possibility that a metabolically-based intervention might have therapeutic value in the management of schizophrenia, a notion supported by our recent results that a low carbohydrate/high-fat therapeutic ketogenic diet (KD) prevented a variety of behavioural abnormalities induced by pharmacological inhibition of NMDA glutamate receptors. Here we asked if the beneficial effects of KD can be generalised to impaired prepulse inhibition of startle (PPI), a translationally validated endophenotype of schizophrenia, in a pharmacological model in mice. Furthermore, we addressed the issue of whether the effect of KD is linked to the calorie-restricted state typical of the initial phase of KD. We fed male C57BL/6 mice a KD for 7 weeks and tested PPI at 3 and 7 weeks, in the presence and absence of a significant digestible energy deficit, respectively. We used an NMDA receptor hypo-function model of schizophrenia induced by acute injection of dizocilpine (MK-801). We found that KD effectively prevented MK-801-induced PPI impairments at both 3 and 7 weeks, irrespective of the presence or absence of digestible energy deficit. Furthermore, there was a lack of correlation between PPI and body weight changes. These results support the efficacy of the therapeutic KD in a translational model of schizophrenia and furthermore provide evidence against the role of calorie restriction in its mechanism of action.

Mice repeatedly exposed to Group-A β-Haemolytic Streptococcus show perseverative behaviors, impaired sensorimotor gating, and immune activation in rostral diencephalon

Repeated exposure to Group-A β-Haemolytic Streptococcus (GAS) may constitute a vulnerability factor in the onset and course of pediatric motor disturbances. GAS infections/colonization can stimulate the production of antibodies, which may cross the blood brain barrier, target selected brain areas (e.g. basal ganglia), and exacerbate motor alterations. Here, we exposed developing SJL male mice to four injections with a GAS homogenate and evaluated the following domains: motor coordination; general locomotion; repetitive behaviors; perseverative responses; and sensorimotor gating (pre-pulse inhibition, PPI). To demonstrate that behavioral changes were associated with immune-mediated brain alterations, we analyzed, in selected brain areas, the presence of infiltrates and microglial activation (immunohistochemistry), monoamines (HPLC), and brain metabolites (in vivo Magnetic Resonance Spectroscopy). GAS-exposed mice showed increased repetitive and perseverative behaviors, impaired PPI, and reduced concentrations of serotonin in prefrontal cortex, a brain area linked to the behavioral domains investigated, wherein they also showed remarkable elevations in lactate. Active inflammatory processes were substantiated by the observation of infiltrates and microglial activation in the white matter of the anterior diencephalon. These data support the hypothesis that repeated GAS exposure may elicit inflammatory responses in brain areas involved in motor control and perseverative behavior, and result in phenotypic abnormalities.

A Methionine-Induced Animal Model of Schizophrenia: Face and Predictive Validity

BACKGROUND

Modulating the methylation process induces broad biochemical changes, some of which may be involved in schizophrenia. Methylation is in particular central to epigenesis, which is also recognized as a factor in the etiology of schizophrenia. Because methionine administration to patients with schizophrenia has been reported to exacerbate their psychotic symptoms and because mice treated with methionine exhibited social deficits and prepulse inhibition impairment, we investigated whether methionine administration could lead to behavioral changes that reflect schizophrenic symptoms in mice.

METHODS

l-Methionine was administered to mice twice a day for 7 days.

RESULTS

We found that this treatment induces behavioral responses that reflect the 3 types of schizophrenia-like symptoms (positive, negative, or cognitive deficits) as monitored in a battery of behavioral assays (locomotion, stereotypy, social interaction, forced swimming, prepulse inhibition, novel object recognition, and inhibitory avoidance). Moreover, these responses were differentially reversed by typical haloperidol and atypical clozapine antipsychotics in ways that parallel their effects in schizophrenics.

CONCLUSION

We thus propose the l-methionine treatment as an animal model recapitulating several symptoms of schizophrenia. We have established the face and predictive validity for this model. Our model relies on an essential natural amino acid and on an intervention that is relatively simple and time effective and may offer an additional tool for assessing novel antipsychotics.

Association of brain immune genes with social behavior of inbred mouse strains

Background

Social deficit is one of the core symptoms of neuropsychiatric diseases, in which immune genes play an important role. Although a few immune genes have been shown to regulate social and emotional behaviors, how immune gene network(s) may jointly regulate sociability has not been investigated so far.

Methods

To decipher the potential immune-mediated mechanisms underlying social behavior, we first studied the brain microarray data of eight inbred mouse strains with known variations in social behavior and retrieved the differentially expressed immune genes. We then made a protein-protein interaction analysis of them to find the major networks and explored the potential association of these genes with the behavior and brain morphology in the mouse phenome database. To validate the expression and function of the candidate immune genes, we selected the C57BL/6 J and DBA/2 J strains among the eight inbred strains, compared their social behaviors in resident-intruder and 3-chambered social tests and the mRNA levels of these genes, and analyzed the correlations of these genes with the social behaviors.

Results

A group of immune genes were differentially expressed in the brains of these mouse strains. The representative C57BL/6 J and DBA/2 J strains displayed significant differences in social behaviors, DBA/2 J mice being less active in social dominance and social interaction than C57BL/6 J mice. The mRNA levels of H2-d1 in the prefrontal cortex, hippocampus, and hypothalamus and C1qb in the hippocampus of the DBA/2 J strain were significantly down-regulated as compared to those in the C57BL/6 J strain. In contrast, Polr3b in the hippocampus and Tnfsf13b in the prefrontal cortex of the DBA/2 J strain were up-regulated. Furthermore, C1qb, Cx3cl1, H2-d1, H2-k1, Polr3b, and Tnfsf13b were predicted to be associated with various behavioral and brain morphological features across the eight inbred strains. Importantly, the C1qb mRNA level was confirmed to be significantly correlated with the sociability in DBA/2 J but not in C57BL/6 J mice.

Conclusions

Our study provided evidence on the association of immune gene network(s) with the brain development and behavior in animals and revealed neurobiological functions of novel brain immune genes that may contribute to social deficiency in animal models of neuropsychiatric disorders.

Differential expression of brain immune genes and schizophrenia-related behavior in C57BL/6N and DBA/2J female mice

Mounting evidence suggests the association of immune genes with complex neuropsychiatric diseases, such as schizophrenia. However, immune gene expression in the brain and their involvement in schizophrenia-related behavior in animal models have not been well studied so far. We analyzed the social (resident-intruder) and sensorimotor gating (pre-pulse inhibition (PPI) of acoustic startle) behaviors, and expression profiles of several brain immune genes in adult C57BL/6N and DBA/2J female mice. Compared to C57BL/6N mice, DBA/2J mice exhibited less social interaction in the resident-intruder test and reduced pre-pulse inhibition. The mRNA levels of Il1b and Il6 genes were significantly higher in the cortex and hypothalamus, while the mRNA level of C1qb was lower in the cortex, hippocampus and hypothalamus of DBA/2J mice compared to C57BL/6N mice. Furthermore, Tnfsf13b was up-regulated in the cortex and hippocampus, and so did Cd47 in the hippocampus, while Cx3cl1 was down-regulated in the cortex of DBA/2J mice. Our study demonstrates the differential expression of several immune genes in C57BL/6N and DBA/2J strains and more importantly provides clues on their potential importance in regulating schizophrenia-related endophenotypes in animal models.

Sensorimotor gating is disrupted by acute but not chronic systemic exposure to caffeine in mice

RATIONALE

Caffeine is a psychostimulant drug that blocks adenosine A₁ and A₂A receptors (A₁Rs and A₂ARs). However, its ability to disrupt early sensory gating as indexed by prepulse inhibition (PPI), which is consistently disrupted by other psychostimulant agents, has never been convincingly demonstrated.

OBJECTIVES

To compare the impact of caffeine on PPI expression in C57BL/6 mice by two dose-response experiments differing in terms of chronicity, regimen, and route of administration. To study separately the acute effect of selective antagonists against A₁R or A₂AR.

METHODS

Caffeine (10, 30, 100 mg/kg, intraperitoneal (i.p.)) was either administered shortly before testing or via caffeinated drinking water (0.3, 1.0, 2 g/l) in home cages over 3 weeks. Two separate dose-response studies tested the acute effect of the selective A₁R antagonist, 1,3 dipropyl-8 cyclopentyl xanthine (DPCPX), and the selective A₂AR antagonist, 5-amino-7-(2-phenylethyl)-2-(2-furyl)-pyrazolo-[4,3-e]-1,2,4-triazolo[1,5-c] (SCH 58261) (0.2, 1.0, 5.0 mg/kg, i.p.). The two drugs were combined in a final experiment to identify their potential synergistic interaction.

RESULTS

While the two lower acute doses of caffeine attenuated PPI, the highest dose potentiated PPI. By contrast, chronic caffeine exposure did not affect PPI. Neither DPCPX nor SCH 58261 altered PPI, and no synergism was observed when the two drugs were combined.

CONCLUSIONS

This is the first demonstration that acute caffeine disrupts PPI, but the relative contribution of A₁R and A₂AR blockade remains unclear, and possible non-adenosinergic mechanisms cannot be ruled out. The null effect under chronic caffeine exposure might involve the development of tolerance, but the precise receptor subtypes involved also warrant further investigation.

Mixed housing with DBA/2 mice induces stress in C57BL/6 mice: implications for interventions based on social enrichment

Several behavioral interventions, based on social enrichment and observational learning are applied in treatment of neuropsychiatric disorders. However, the mechanism of such modulatory effect and the safety of applied methods on individuals involved in social support need further investigation. We took advantage of known differences between inbred mouse strains to reveal the effect of social enrichment on behavior and neurobiology of animals with different behavioral phenotypes. C57BL/6 and DBA/2 female mice displaying multiple differences in cognitive, social, and emotional behavior were group-housed either in same-strain or in mixed-strain conditions. Comprehensive behavioral phenotyping and analysis of expression of several plasticity- and stress-related genes were done to measure the reciprocal effects of social interaction between the strains. Contrary to our expectation, mixed housing did not change the behavior of DBA/2 mice. Nevertheless, the level of serum corticosterone and the expression of glucocorticoid receptor Nr3c1 in the brain were increased in mixed housed DBA/2 as compared with those of separately housed DBA/2 mice. In contrast, socially active C57BL/6 animals were more sensitive to the mixed housing, displaying several signs of stress: alterations in learning, social, and anxiety-like behavior and anhedonia. These behavioral impairments were accompanied by the elevated serum corticosterone and the reduced expression of Nr3c1, as well as the elevated Bdnf levels in the cortex and hippocampus. Our results demonstrate the importance of social factors in modulation of both behavior and the underlying neurobiological mechanisms in stress response, and draw attention to the potential negative impact of social interventions for individuals involved in social support.

Modeling combined schizophrenia-related behavioral and metabolic phenotypes in rodents

Schizophrenia is a chronic, debilitating disorder with a complex behavioral and cognitive phenotype underlined by a similarly complex etiology involving an interaction between susceptibility genes and environmental factors during early development. Limited progress has been made in developing novel pharmacotherapy, partly due to a lack of valid animal models. The recent recognition of the potentially causal role of central and peripheral energy metabolism in the pathophysiology of schizophrenia raises the need of research on animal models that combine both behavioral and metabolic phenotypic domains, similar to what have been identified in humans. In this review we focus on selected genetic (DBA/2J mice, leptin receptor mutants, and PSD-93 knockout mice), early neurodevelopmental (maternal protein deprivation) and pharmacological (acute phencyclidine) animal models that capture the combined behavioral and metabolic abnormalities shown by schizophrenic patients. In reviewing behavioral phenotypes relevant to schizophrenia we apply the principles established by the Research Domain Criteria (RDoC) for better translation. We demonstrate that etiologically diverse manipulations such as specific breeding, deletion of genes that are primarily involved in metabolic regulation and in synaptic plasticity, as well as early metabolic deprivation and adult pharmacological challenge of the glutamate system can lead to schizophrenia-related behavioral and metabolic phenotypes, which suggest that these pathways might be interlinked. We propose that using animal models that combine different domains of schizophrenia can be used as a translationally valid approach to capture the system-level complex interplay between peripheral and central processes in the development of psychopathology.

Positive allosteric modulation of GABAB receptors ameliorates sensorimotor gating in rodent models

BACKGROUND

Converging evidence points to the involvement of γ-amino-butyric acid B receptors (GABABRs) in the regulation of information processing. We previously showed that GABABR agonists exhibit antipsychotic-like properties in rodent models of sensorimotor gating deficits, as measured by the prepulse inhibition (PPI) of the acoustic startle reflex. The therapeutic potential of these agents, however, is limited by their neuromuscular side effects; thus, in this study, we analyzed whether rac-BHFF, a potent GABABR-positive allosteric modulator (PAM), could counter spontaneous and pharmacologically induced PPI deficits across various rodent models.

METHODS

We tested the antipsychotic effects of rac-BHFF on the PPI deficits caused by the N-methyl-D-aspartate glutamate receptor antagonist dizocilpine, in Sprague-Dawley rats and C57BL/6 mice. Furthermore, we verified whether rac-BHFF ameliorated the spontaneous PPI impairments in DBA/2J mice.

RESULTS

rac-BHFF dose-dependently countered the PPI deficits across all three models, in a fashion akin to the GABABR agonist baclofen and the atypical antipsychotic clozapine; in contrast with these compounds, however, rac-BHFF did not affect startle magnitude.

CONCLUSIONS

The present data further support the implication of GABABRs in the modulation of sensorimotor gating and point to their PAMs as a novel promising tool for antipsychotic treatment, with fewer side effects than GABABR agonists.

CRF1 receptor antagonists do not reverse pharmacological disruption of prepulse inhibition in rodents

RATIONALE

As enhanced corticotropin-releasing factor (CRF) transmission is associated with induction of sensorimotor gating deficits, CRF₁ receptor antagonists may reverse disrupted prepulse inhibition (PPI), an operational measure of sensorimotor gating.

OBJECTIVES

To determine the effects of CRF₁ receptor antagonists in pharmacological models of disrupted PPI and to determine if long-term elevated central CRF levels alter sensitivity towards PPI disrupting drugs.

METHODS

CP154,526 (10-40 mg/kg), SSR125543 (3-30 mg/kg) and DMP695 (40 mg/kg) were tested on PPI disruption provoked by D-amphetamine (2.5, 3 mg/kg), ketamine (5, 30 mg/kg) and MK801 (0.2, 0.5 mg/kg) in Wistar rats, C57Bl/6J and CD1 mice, and on spontaneously low PPI in Iffa Credo rats and DBA/2J mice. PPI-disrupting effects of D-amphetamine (2.5-5 mg/kg) and MK801 (0.3-1 mg/kg) were examined in CRF-overexpressing (CRFtg) mice, which display PPI deficits. Finally, we determined the influence of CP154,526 on D-amphetamine-induced dopamine outflow in nucleus accumbens and prefrontal cortex of CRFtg mice using in vivo microdialysis.

RESULTS

No CRF₁-antagonists improved PPI deficits in any test. CRFtg mice showed blunted PPI disruption in response to MK801, but not D-amphetamine. Further, D-amphetamine-induced dopamine release was less pronounced in CRFtg versus wild-type mice, a response normalized by pretreatment with CP154,526.

CONCLUSION

The inability of CRF₁ receptor antagonists to block pharmacological disruption of sensorimotor gating suggests that the involvement of CRF₁ receptors in the modulation of dopaminergic and glutamatergic neurotransmission relevant for sensory gating is limited. Furthermore, the alterations observed in CRFtg mice support the notion that long-term elevated central CRF levels induce changes in these neurotransmitter systems.

SSR504734 enhances basal expression of prepulse inhibition but exacerbates the disruption of prepulse inhibition by apomorphine

RATIONALE

Inhibition of glycine transporter 1 (GlyT1) elevates extracellular glycine and can thus increase N-methyl-D-aspartate receptor (NMDAR) excitability in the brain. The potent GlyT1 inhibitor, SSR504734, has also been shown to potentiate the behavioral effects of direct and indirect dopamine agonists. Thus, an acute systemic dose of SSR504734 was sufficient to exacerbate the motor-stimulant effect of the dopamine releaser amphetamine in C57BL/6 mice, even though SSR504734 alone exerted no significant effect on motor activity.

OBJECTIVES

Here, we explore if SSR504734 might modulate dopamine-dependent sensory gating in the paradigm of prepulse inhibition (PPI) of the acoustic startle reflex.

METHODS

Experiment 1 characterized the effect of SSR504734 (10 and 30 mg/kg i.p.) on PPI expression when administered alone. Experiments 2 and 3 investigated the impact of SSR504734 when administered in conjunction with the dopamine receptor agonist, apomorphine (1 and 2 mg/kg s.c.), which is known to reliably disrupt PPI.

RESULTS

When administered alone, acute SSR504734 enhanced PPI only at 30 mg/kg--a dose that has been shown to improve cognitive functions including working memory, which has been linked to enhanced NMDAR function resulting from the elevation of extracellular glycine. However, this effect did not allow SSR504734 to antagonize the PPI-disruptive effect of apomorphine. At the lower dose of 10 mg/kg--that was insufficient to enhance PPI when administered alone--SSR504734 even exacerbated the deleterious effect of apomorphine on PPI.

CONCLUSIONS

The therapeutic potential of GlyT1 inhibition against distinct behavioral/cognitive deficiency might require different magnitudes of GlyT1 inhibition.

Novel drug-regulated transcriptional networks in brain reveal pharmacological properties of psychotropic drugs

Background

Despite their widespread use, the biological mechanisms underlying the efficacy of psychotropic drugs are still incompletely known; improved understanding of these is essential for development of novel more effective drugs and rational design of therapy. Given the large number of psychotropic drugs available and their differential pharmacological effects, it would be important to establish specific predictors of response to various classes of drugs.

Results

To identify the molecular mechanisms that may initiate therapeutic effects, whole-genome expression profiling (using 324 Illumina Mouse WG-6 microarrays) of drug-induced alterations in the mouse brain was undertaken, with a focus on the time-course (1, 2, 4 and 8 h) of gene expression changes produced by eighteen major psychotropic drugs: antidepressants, antipsychotics, anxiolytics, psychostimulants and opioids. The resulting database is freely accessible at http://www.genes2mind.org. Bioinformatics approaches led to the identification of three main drug-responsive genomic networks and indicated neurobiological pathways that mediate the alterations in transcription. Each tested psychotropic drug was characterized by a unique gene network expression profile related to its neuropharmacological properties. Functional links that connect expression of the networks to the development of neuronal adaptations (MAPK signaling pathway), control of brain metabolism (adipocytokine pathway), and organization of cell projections (mTOR pathway) were found.

Conclusions

The comparison of gene expression alterations between various drugs opened a new means to classify the different psychoactive compounds and to predict their cellular targets; this is well exemplified in the case of tianeptine, an antidepressant with unknown mechanisms of action. This work represents the first proof-of-concept study of a molecular classification of psychoactive drugs.

Mouse strain differences in phencyclidine-induced behavioural changes

Administration of phencyclidine (PCP) is acknowledged to generate a model of psychosis in animals. With the identification of genetic susceptibility factors for schizophrenia and bipolar disorder, great efforts have been made to generate genetic animal models for major mental illnesses. As these disorders are multifactorial, comparisons among drug-induced (non-genetic) and genetic models are becoming an important issue in biological psychiatry. A major barrier is that the standard mouse strain used in the generation of genetic models is C57BL/6, whereas almost all studies with PCP-induced models have utilized other strains. To fill this technical gap, we systematically compared the behavioural changes upon PCP administration in different mouse strains, including C57BL/6N, C57BL/6J, ddY, and ICR. We observed strain differences in PCP-induced hyperlocomotion and enhanced immobility in the forced swim test (ddY>>C57BL/6N and 6J>ICR). In contrast, there was no strain difference in the impairment of recognition memory in the novel object recognition memory test after withdrawal of chronic PCP administration. This study provides practical guidance for comparing genetic with PCP-induced models of psychosis in C57BL/6. Furthermore, such strain differences may provide a clue to the biological mechanisms underlying PCP-induced endophenotypes possibly relevant to major mental illnesses.

Dual inhibitor of PDE7 and GSK-3-VP1.15 acts as antipsychotic and cognitive enhancer in C57BL/6J mice

Cognitive deficit is a core of schizophrenia and it is not effectively treated by the available antipsychotic drugs, hence new and more effective therapy is needed. Schizophrenia is considered as a pathway disorder where Disrupted-In-Schizophrenia-1 (DISC1) is important molecular player that regulates multiple cellular cascades. We recently reported synergistic action between phosphodiesterase-4 (PDE4) and glycogen synthase kinase-3 (GSK-3) as DISC1 interacting proteins. In the current study we characterized behavioural effects of a newly developed compound, VP1.15 that inhibits both PDE7 and GSK-3 with main focus on its antipsychotic and cognitive capacities. VP1.15 reduced ambulation in C57BL/6J mice in a dose-dependent manner (7.5 mg/kg and 3 mg/kg, respectively) and, hence, lower dose was chosen for the further analysis. VP1.1.5 facilitated pre-pulse inhibition (PPI), reversed amphetamine- but not MK-801-induced PPI deficit. The drug was able to ameliorate the disrupted latent inhibition (LI) induced by the increased number of conditioning trials and reversed amphetamine-induced LI deficit, supporting further its antipsychotic effects. The drug also significantly improved episodic memory in the spatial object recognition test, facilitated working memory in Y-maze and enhanced cued fear memory, but had no effect on executive function in the Puzzle box and contextual fear conditioning. Taken together, VP1.15 elicited antipsychotic effects and also facilitated cognitive domains in mice, suggesting that multitarget drugs, affecting molecular substrates from the same pathway, perhaps could be antipsychotics of new-generation that open a new possibilities in drug discoveries. This article is part of a Special Issue entitled 'Cognitive Enhancers'.

Effects of α7 nicotinic acetylcholine receptor agonists on antipsychotic efficacy in a preclinical mouse model of psychosis

RATIONALE

Antipsychotics normalize responses in the DBA/2 mouse model of prepulse inhibition (PPI), a preclinical model of sensorimotor gating deficits. The α7 nicotinic acetylcholine receptor (nAChR) as a molecular target is considered an attractive approach for improvement of cognitive deficits in schizophrenia (CDS). Assessment of clinical efficacy of novel agents in CDS involves treating patients already on antipsychotic medications.

OBJECTIVE

We evaluated the effects of the combination of α7 nAChR agonists ABT-107 (0.1-10.0 mg/kg i.p.), A-582941 (0.04-4.0 mg/kg i.p.), and PNU282987 (1.0-10.0 mg/kg i.p.) with risperidone (0.1-1.0 mg/kg i.p.) or haloperidol (0.3-3.0 mg/kg i.p.), representative atypical and typical antipsychotic agents in the DBA/2 mouse PPI model. The same α7 agonists were given alone or in combination with a dose of antipsychotic medication that induces a minimal level of catalepsy in rats, an assay with predictive validity for the induction of extrapyramidal symptoms.

RESULTS

The α7 nAChR agonists ABT-107, A-582941, and PNU282987 had no effect in DBA/2 mouse PPI when given alone yet increased the effects of haloperidol and risperidone. The α7 nAChR agonists did not cause catalepsy in rats, nor did they enhance antipsychotic-induced catalepsy.

CONCLUSIONS

When given in combination with either a typical or atypical antipsychotic, α7 nAChR agonists did not impair efficacy in the DBA/2 J mouse PPI model. The efficacy but not the motoric side effects of antipsychotics was enhanced, suggesting that adjunctive therapy of α7 nAChR agonists not only could be useful for the treatment of cognitive deficits associated with schizophrenia but also could enhance the efficacy against positive symptoms.

Parametric and pharmacological modulations of latent inhibition in mouse inbred strains

Latent inhibition (LI) is a cross species selective attention phenomenon, which is disrupted by amphetamine and enhanced by antipsychotic drugs (APDs). Accumulating data of LI in gene-modified mice as well as in mouse inbred strains suggest genetic component of LI. Here we study modulation of LI in mouse inbred strains with spontaneously disrupted LI by parametric manipulations (number of pre-exposures and conditioning trials) and pharmacological treatments with antipsychotics and NMDA modulator, D-serine. C3H/He and CBA/J inbred mice showed disrupted LI under conditions with 40 pre-exposures (PE) and 2 trials of the conditioned stimulus-unconditioned stimulus (CS-US) due to either loss of the pre-exposure effect or a ceiling effect of poor learning, respectively. The increased number of pre-exposures and/or number of conditioning trials corrected expression of LI in these inbred mice. The disrupted LI was also reversed by haloperidol in both inbred strains at 1.2 mg/kg but not at 0.4 mg/kg, as well as by clozapine (at 3 mg/kg in C3H/He and at 9 mg/kg in CBA/J mice). D-serine potentiated LI in C3H/He mice at 600 mg/kg, but not in the CBA/J at both studied doses (600 and 1800 mg/kg). Desipramine (10 mg/kg) had no effect on LI in both inbred mouse strains. Our findings demonstrated some resemblance between the effects of parametric and pharmacological manipulations on LI, suggesting that APDs may affect the capacity of the brain processes environmental stimuli in LI. Taken together, LI may offer a translational strategy that allows prediction of drug efficacy for cognitive impairments in schizophrenia.

Strain-dependent changes in acoustic startle response and its plasticity across adolescence in mice

Acoustic startle response and its plasticity, e.g., habituation and prepulse inhibition (PPI), have been extensively investigated, being altered in several neuropsychiatric disorders. Yet, little is known about the expression of startle-related behaviors during adolescence, a critical phase in the development of a variety of major neuropsychiatric pathologies. The present study investigated for the first time startle behaviors across adolescence in male mice of the inbred strains C57BL/6J and DBA/2J. Pre-pubertal (4 weeks of age) mice displayed reduced startle reactivity and altered PPI compared to adult animals (8 weeks of age), but these effects were observed only in the C57BL/6J strain. Strain differences were also clearly detected for startle response, habituation, and PPI. All effects were modulated by the intensity of the pulse stimulus and were not confounded by differences in anxiety levels. Our data demonstrate that genetic factors and the early adolescent phase are critically important considerations in the design of mouse models of neuropsychiatric disturbances.

The effect of thiamin tetrahydrofurfuryl disulfide on behavior of juvenile DBA/2J mice

Due to genetic defects or illness some individuals require higher amounts of thiamin than are typically provided by the diet. Lipid-soluble thiamin precursors can achieve high blood levels of thiamin and result in increased concentrations in the central nervous system. High intakes of thiamin have been reported as beneficial in children with autism and attention deficit/hyperactivity disorder. The current study examined the effect of thiamin tetrahydrofurfuryl disulfide (TTFD), a lipophilic precursor, on behavior in the juvenile male DBA/2J mouse. Mice given by oral gavage deionized water or deionized water providing 100 mg or 340 mg TTFD/kg body weight daily for 17 d, starting at postnatal day 18, were tested for effects on operant learning, social interaction, general activity level, and prepulse inhibition of acoustic startle, as well as effects on growth and select organ weights. Results indicate lower activity and altered social interaction at both treatment levels and decreased acoustic startle at the 100 mg/kg level. Compared to controls, percent weight gain was lower in the TTFD-treatment groups, but percent body length increase was not affected by TTFD treatment. TTFD treatment did not influence percent organ weights as percentage of body weights. TTFD treatment resulted in increased whole brain thiamin concentrations. These results support the concept that lipophilic thiamin precursors provided during early development can affect a number of behavioral parameters. In clinical trials with children with behavior disorders, attention should be given to preventing possible adverse gastrointestinal irritant effects associated with TTFD therapy.

Targeting the nicotinic alpha7 acetylcholine receptor to enhance cognition in disease

A promising drug target currently under investigation to improve cognitive deficits in neuropsychiatric and neurological disorders is the neuronal nicotinic alpha7 acetylcholine receptor (α7nAChR). Improving cognitive impairments in diseases such as Alzheimer's (AD) and schizophrenia remains a large unmet medical need, and the α7nAChR has many properties that make it an attractive therapeutic target. The α7nAChR is a ligand gated ion channel that has particularly high permeability to Ca(2+) and is expressed in key brain regions involved in cognitive processes (e.g., hippocampus). The α7nAChRs are localized both pre-synaptically, where they can regulate neurotransmitter release, and post-synaptically where they can activate intracellular signaling cascades and influence downstream processes involved in learning and memory. In particular, activation of the α7nAChR with small molecule agonists enhances long-term potentiation, an in vitro model of synaptic plasticity, and improves performance across multiple cognitive domains in rodents, monkeys, and humans. Positive allosteric modulation of the α7nAChR offers an alternate approach to direct agonism that could prove to be particularly beneficial in certain disease populations where smoking nicotine is prevalent (e.g., schizophrenia) and could interfere with an orthosteric agonist approach. The current review focuses on the neurobiology of the α7nAChR, its role in cognition and the development status of some of the most promising molecules advancing for the treatment of cognitive dysfunction in disease.

Prepulse inhibition of the startle reflex and response to antipsychotic treatments in two outbred mouse strains in comparison to the inbred DBA/2 mouse

RATIONALE

Naturally low prepulse inhibition (PPI) in DBA/2 mice is increased by marketed antipsychotics and compounds acting at novel targets relevant to schizophrenia. Whether other mouse strains with naturally low PPI respond similarly and could be translational models of schizophrenia is unknown.

OBJECTIVE

Baseline levels of PPI were determined in outbred CF-1 and Black Swiss mice. CF-1 and Black Swiss mice were then compared to DBA/2 mice for their responses to typical (haloperidol) and atypical (clozapine) antipsychotics and to compounds with potential antipsychotic activity, a histamine H(3) receptor antagonist (thioperamide) and a glycine transporter-1 inhibitor (SSR504734).

RESULTS

CF-1 and Black Swiss mice had naturally low PPI, similar to the level in C57BL/6 mice, but higher than that in DBA/2 mice. Haloperidol (0.3-1 mg/kg) increased PPI in DBA/2, CF-1, and Black Swiss mice. Clozapine (3 mg/kg) increased PPI in DBA/2 and CF-1 mice, but not in Black Swiss mice. Thioperamide (10-30 mg/kg) and SSR504734 (30 mg/kg) increased PPI only in DBA/2 mice. Strain differences in PPI responsiveness were not due to differences in brain concentrations of the tested compounds.

CONCLUSIONS

CF-1 mice with naturally low PPI may be useful for testing typical and atypical antipsychotics while Black Swiss mice only responded to a typical antipsychotic. DBA/2 mice remain the only strain with naturally low PPI that responds to marketed antipsychotics, as well as to compounds with novel mechanisms of action. Thus, DBA/2 mice may be the strain of choice for screening novel chemical entities for their ability to increase PPI.

Modulation of sensorimotor gating in prepulse inhibition by conditional brain glycine transporter 1 deletion in mice

Inhibition of glycine transporter 1 (GlyT1) augments N-methyl-D-aspartate receptor (NMDAR)-mediated transmission and represents a potential antipsychotic drug target according to the NMDAR hypofunction hypothesis of schizophrenia. Preclinical evaluation of GlyT1 inhibiting drugs using the prepulse inhibition (PPI) test, however, has yielded mixed outcomes. Here, we tested for the first time the impact of two conditional knockouts of GlyT1 on PPI expression. Complete deletion of GlyT1 in the cerebral cortices confers resistance to PPI disruption induced by the NMDAR blocker MK-801 (0.2mg/kg, i.p.) without affecting PPI expression in unchallenged conditions. In contrast, restricting GlyT1 deletion to neurons in forebrain including the striatum significantly attenuated PPI, and the animals remained sensitive to the PPI-disruptive effect of MK-801 at the same dose. These results demonstrate in mice that depending on the regional and/or cell-type specificity, deletion of the GlyT1 gene could yield divergent effects on PPI.

Involvement of the cholinergic system in conditioning and perceptual memory

The cholinergic systems play a pivotal role in learning and memory, and have been the centre of attention when it comes to diseases containing cognitive deficits. It is therefore not surprising, that the cholinergic transmitter system has experienced detailed examination of its role in numerous behavioural situations not least with the perspective that cognition may be rescued with appropriate cholinergic 'boosters'. Here we reviewed the literature on (i) cholinergic lesions, (ii) pharmacological intervention of muscarinic or nicotinic system, or (iii) genetic deletion of selective receptor subtypes with respect to sensory discrimination and conditioning procedures. We consider visual, auditory, olfactory and somatosensory processing first before discussing more complex tasks such as startle responses, latent inhibition, negative patterning, eye blink and fear conditioning, and passive avoidance paradigms. An overarching reoccurring theme is that lesions of the cholinergic projection neurones of the basal forebrain impact negatively on acquisition learning in these paradigms and blockade of muscarinic (and to a lesser extent nicotinic) receptors in the target structures produce similar behavioural deficits. While these pertain mainly to impairments in acquisition learning, some rare cases extend to memory consolidation. Such single case observations warranted replication and more in-depth studies. Intriguingly, receptor blockade or receptor gene knockout repeatedly produced contradictory results (for example in fear conditioning) and combined studies, in which genetically altered mice are pharmacological manipulated, are so far missing. However, they are desperately needed to clarify underlying reasons for these contradictions. Consistently, stimulation of either muscarinic (mainly M(1)) or nicotinic (predominantly α7) receptors was beneficial for learning and memory formation across all paradigms supporting the notion that research into the development and mechanisms of novel and better cholinomimetics may prove useful in the treatment of neurodegenerative or psychiatric disorders with cognitive endophenotypes.

Sensorimotor gating and vigilance-dependent choice accuracy: a within-subject correlative analysis in wild-type C57BL/6 mice

Deterioration in attention and related processes is an early sign in schizophrenia predictive of disease development. Amongst the various translational paradigms for assessing attention in rodents, it is not known if they are equivalent in detecting individual differences. Answers here are pertinent to their use in the general human population for identifying individuals at high risk of developing schizophrenia. The present study employed a within-subject approach to examine in mice two common paradigms for assessing attention that differ markedly in their implementation. An operant-based two-choice visual discrimination task (2-CVDT) that depends on effortful attention to brief visual cues was contrasted with prepulse inhibition (PPI) of the acoustic startle reflex, a well-established test of pre-attentive gating whereby processing of a startle-eliciting stimulus is inhibited by a preceding weak prepulse stimulus. Here, we revealed a correlation showing that individual mice with low PPI tended to perform poorly in the 2-CVDT in terms of choice accuracy but not response speed. This specific positive correlation suggests that the two readouts might be regulated via common attentional mechanisms, which might be critically dependent on normal muscarinic and N-methyl-d-asparate receptor functions. As demonstrated here, blockade of either receptor type by scopolamine or dizocilpine impaired 2-CVDT performance at doses that have been shown to disrupt PPI in mice. Further studies contrasting these two paradigms would be warranted to characterize the possible underlying psychological constructs that give rise to this correlation and to clarify whether the two paradigms may effectively capture schizophrenia-related cognitive deficits belonging to orthogonal domains.

Enhanced dopamine function in DISC1-L100P mutant mice: implications for schizophrenia

Significant advances have been made in understanding the role of disrupted-in-schizophrenia-1 (DISC1) in the brain and accumulating findings suggest the possible implication of DISC1 in the regulation of dopamine (DA) function. A mutation in the second exon of DISC1 at L100P leads to the development of schizophrenia-related behavior in mutant mice (DISC1-L100P). We investigated here the role of DA in the expression of schizophrenia-related endophenotypes in the DISC1-L100P genetic mouse model. The mutated DISC1 resulted in facilitation of the psychostimulant effect of amphetamine in DISC1-L100P mutant mice assessed in the open field and prepulse inhibition (PPI) tests. Biochemical studies detected a 2.1-fold increase in the proportion of striatal D receptors without significant changes in DA release in vivo in the striatum of DISC1-L100P mutants in response to the low dose of amphetamine. The D(2) receptor antagonist haloperidol reversed the hyperactivity, PPI and latent inhibition (LI) deficits and blocked the psychostimulant effect of amphetamine in DISC1-L100P mutants. Taken together, our findings show the role of DISC1 in D(2) -related pathophysiological mechanism of schizophrenia, linking DISC1 with well-established DA hypothesis of schizophrenia.

The effects of d-amphetamine, methylphenidate, sydnocarb, and caffeine on prepulse inhibition of the startle reflex in DBA/2 mice

RATIONALE

Dopamine (DA) agonists decrease prepulse inhibition (PPI) and are widely used in translational models for the sensorimotor gating deficits in schizophrenia. Reductions in PPI induced by DA agonists are routinely reversed by antipsychotics in these translational models. Nevertheless, under conditions of low-baseline PPI, DA agonists may increase PPI in humans and experimental animals. DBA/2 mice have naturally low-baseline PPI, which as in the drug-induced translational models, is increased by antipsychotics.

OBJECTIVE

Determine whether DBA/2 mice respond like other models of low-baseline PPI by evaluating the effect of psychostimulants (caffeine, 30-100 mg/kg IP) and the indirect DA agonists d-amphetamine (0.3-10 mg/kg IP), methylphenidate (10-100 mg/kg IP), and sydnocarb (10-30 mg/kg IP), a selective DA transporter inhibitor on PPI. Furthermore, baseline PPI in DBA/2 mice was increased by noise exposure and the effect of d-amphetamine was assessed.

RESULTS

PPI was increased at one dose for each of the psychostimulants when baseline PPI was low in naïve DBA/2 mice. Effective doses were 3 mg/kg of d-amphetamine, 30 mg/kg of methylphenidate, 30 mg/kg of sydnocarb, and 100 mg/kg of caffeine. Higher doses of d-amphetamine (10 mg/kg) and methylphenidate (100 mg/kg IP) decreased PPI. When the baseline PPI was increased by noise exposure, 10 mg/kg of d-amphetamine only reduced PPI.

CONCLUSION

Lower doses of psychostimulants increased PPI in naïve DBA/2 mice in a manner consistent with their naturally low-baseline PPI, and higher doses decreased PPI, consistent with effects observed in most mouse strains.

Glycine transporter (GlyT1) inhibitors with reduced residence time increase prepulse inhibition without inducing hyperlocomotion in DBA/2 mice

Inhibition of the glycine transporter type 1 (GlyT1) leading to potentiation of the glycine site (GlyB) on the N-methyl-d-aspartate (NMDA) receptor has been proposed as a novel therapeutic approach for schizophrenia. However, sarcosine-based GlyT1 inhibitors produce undesirable side effects including compulsive walking and respiratory distress. The influence of specific biochemical properties of GlyT1 inhibitors, such as mode of inhibition and residence time, on adverse effects is unknown. Two GlyT1 inhibitors that contain a sarcosine moiety, sarcosine and ALX-5407, and two compounds that do not contain a sarcosine moiety, Roche-7 and Merck (S)-13h, were evaluated for their potency, mode of inhibition, and target residence times in vitro, and modulation of prepulse inhibition (PPI) and locomotor activity in vivo. (S)-13h and sarcosine were competitive inhibitors while ALX-5407 and Roche-7 demonstrated mixed noncompetitive inhibition. Potency of GlyT1 inhibition (ALX-5407>(S)-13h>Roche-7≫sarcosine) did not correlate with residence time on GlyT1 (sarcosine=Roche-7≪(S)-13h<ALX-5407). ALX-5407 and (S)-13h induced compulsive walking, termed obstinate progression (OP), at doses that increased PPI in DBA/2 mice, demonstrating that OP was not a function of mode of inhibition or inhibitor chemotype. Sarcosine and Roche-7 increased PPI without inducing OP, suggesting that compounds with decreased GlyT1 residence time were efficacious without adverse effects. Direct activation of the GlyB site by d-serine did not produce OP. However, OP induced by (S)-13h was blocked by strychnine, a glycine receptor (GlyA) antagonist, suggesting that OP induced by GlyT1 inhibition was mediated by GlyA. Thus, GlyT1 inhibitors with short residence times demonstrated efficacy without mechanism-based adverse effects.

Pharmacological effects of metabotropic glutamate receptor ligands on prepulse inhibition in DBA/2J mice

Schizophrenic patients typically exhibit impairment of sensorimotor gating, which can be modeled in animals using acoustic prepulse inhibition of the startle. Both classical and atypical antipsychotics have been shown to improve prepulse inhibition in DBA/2J mice, a non-pharmacological model for impaired sensorimotor gating. The purpose of the present study was to clarify whether metabotropic glutamate receptors participate in control of sensorimotor gating. We evaluated various metabotropic glutamate receptor ligands on prepulse inhibition in DBA/2J mice. This basal level of prepulse inhibition in DBA/2J mice was increased by only the mGlu(1) receptor antagonists [2-cyclopropyl-5-[1-(2-fluoro-3-pyridinyl)-5-methyl-1H-1,2,3-triazol-4-yl]-2,3-dihydro-1H-isoindol-1-one] (CFMTI), 6-amino-N-cyclohexyl-N,3-dimethylthiazolo[3,2-alpha]benzimidazole-2-carboxamide hydrochloride (YM-298198), and (3,4-dihydro-2H-pyrano[2,3-b]quinolin-7-yl)-(cis-4-methoxycyclohexyl)-methanone (JNJ16259685). There was no effect after treatments with the mGlu(5) receptor antagonist 2-methyl-6-(phenylethynyl)pyridine hydrochloride (MPEP), the mGlu(2/3) receptor agonist (-)-2-oxa-4-aminobicyclo[3.1.0]hexane-4,6-dicarboxylate (LY379268), the mGlu(2/3) receptor antagonist (2S)-2-amino-2-[(1S,2S)-2-carboxycycloprop-1-yl]-3-(xanth-9-yl) propanoic acid (LY341495), the mGlu(7) receptor agonist N,N'-dibenzhydrylethane-1,2-diamine dihydrochloride (AMN082), the mGlu(7) receptor antagonist 6-(4-methoxyphenyl)-5-methyl-3-pyridin-4-ylisoxazonolo[4,5-c]pyridin-4(5H)-one (MMPIP), or the mGlu(8) receptor agonist (S)-3,4-dicarboxyphenylglycine (DCPG). These findings indicate that inhibition of mGlu(1) receptor selectively increases prepulse inhibition in DBA/2J mice and suggest that mGlu(1) receptor antagonists could be a novel treatment for some aspects of schizophrenia.

Behavioral and neurobiological changes in C57BL/6 mouse exposed to cuprizone: effects of antipsychotics

Recent human studies suggest a role for altered oligodendrocytes in the pathophysiology of schizophrenia. Our recent animal study has reported some schizophrenia-like behaviors in mice exposed to cuprizone (Xu et al., 2009), a copper chelator that has been shown to selectively damage the white matter. This study was to explore mechanisms underlying the behavioral changes in cuprizone-exposed mice and to examine effects of the antipsychotics haloperidol, clozapine and quetiapine on the changes in the mice. Mice given cuprizone for 14 days showed a deficit in the prepulse inhibition of acoustic startle response and higher dopamine in the prefrontal cortex (PFC), which changes were not seen in mice given cuprizone plus antipsychotics. Mice given cuprizone for 21 days showed lower spontaneous alternations in Y-maze, which was not seen in mice treated with cuprizone plus the antipsychotics. Mice given cuprizone for 28 days displayed less social interactions, which was not seen in mice given cuprizone plus clozapine/quetiapine, but was seen in mice given cuprizone plus haloperidol. Mice given cuprizone for 42 days showed myelin sheath loss and lower myelin basic protein in PFC, caudate putamen, and hippocampus. The white matter damage in PFC was attenuated in mice given cuprizone plus clozapine/haloperidol. But the white matter damage in caudate putamen and hippocampus was only attenuated by clozapine and quetiapine, not by haloperidol. These results help us to understand the behavioral changes and provide experimental evidence for the protective effects of antipsychotics on white matter damage in cuprizone-exposed mice.

Modeling the positive symptoms of schizophrenia in genetically modified mice: pharmacology and methodology aspects

In recent years, there have been huge advances in the use of genetically modified mice to study pathophysiological mechanisms involved in schizophrenia. This has allowed rapid progress in our understanding of the role of several proposed gene mechanisms in schizophrenia, and yet this research has also revealed how much still remains unresolved. Behavioral studies in genetically modified mice are reviewed with special emphasis on modeling psychotic-like behavior. I will particularly focus on observations on locomotor hyperactivity and disruptions of prepulse inhibition (PPI). Recommendations are included to address pharmacological and methodological aspects in future studies. Mouse models of dopaminergic and glutamatergic dysfunction are then discussed, reflecting the most important and widely studied neurotransmitter systems in schizophrenia. Subsequently, psychosis-like behavior in mice with modifications in the most widely studied schizophrenia susceptibility genes is reviewed. Taken together, the available studies reveal a wealth of available data which have already provided crucial new insight and mechanistic clues which could lead to new treatments or even prevention strategies for schizophrenia.

Serotonin transporter, 5-HT1A receptor, and behavior in DBA/2J mice in comparison with four inbred mouse strains

Prepulse inhibition (PPI), the reduction in acoustic startle produced when it is preceded by a weak prepulse stimulus, is impaired in schizophrenic patients. The DBA/2J mouse strain displayed deficient PPI and is therefore suggested as an experimental animal model for the loss of sensorimotor gating in schizophrenia. Brain serotonin (5-HT) has been implicated in the pathophysiology of several psychiatric disorders, including major depressive disorder and schizophrenia. In the present study, behavior, 5-HT transporter (5-HTT) mRNA level, 5-HT(1A) receptor mRNA level, and 5-HT(1A) receptor density in the brain regions were studied in DBA/2J mice in comparison with four inbred mouse strains (CBA/Lac, C57BL/6, BALB/c, and ICR). A decrease in 5-HTT mRNA level in the midbrain and a reduced density of 5-HT(1A) receptors in the frontal cortex without significant changes in 5-HT(1A) receptor mRNA level in DBA/2J mice were found. It was shown that, along with decreased PPI, DBA/2J mice demonstrated considerably reduced immobility in the tail suspension test and in the forced swim test. No significant interstrain differences in intermale aggression, or in light-dark box and elevated plus-maze tests, were found. The results suggested the involvement of decreased 5-HTT gene expression and 5-HT(1A) receptor density in genetically defined PPI deficiency and showed a lack of any association between PPI deficiency and predisposition to aggressive, anxiety, and depressive-like behaviors.

Are DBA/2 mice associated with schizophrenia-like endophenotypes? A behavioural contrast with C57BL/6 mice

RATIONALE

Due to its intrinsic deficiency in prepulse inhibition (PPI), the inbred DBA/2 mouse strain has been considered as an animal model for evaluating antipsychotic drugs. However, the PPI impairment observed in DBA/2 mice relative to the common C57BL/6 strain is confounded by a concomitant reduction in baseline startle reactivity. In this study, we examined the robustness of the PPI deficit when this confound is fully taken into account.

MATERIALS AND METHODS

Male DBA/2 and C57BL/6 mice were compared in a PPI experiment using multiple pulse stimulus intensities, allowing the possible matching of startle reactivity prior to examination of PPI. The known PPI-enhancing effect of the antipsychotic, clozapine, was then evaluated in half of the animals, whilst the other half was subjected to two additional schizophrenia-relevant behavioural tests: latent inhibition (LI) and locomotor reaction to the psychostimulants-amphetamine and phencyclidine.

RESULTS

PPI deficiency in DBA/2 relative to C57BL/6 mice was essentially independent of the strain difference in baseline startle reactivity. Yet, there was no evidence that DBA/2 mice were superior in detecting the PPI-facilitating effect of clozapine when startle difference was balanced. Compared with C57BL/6 mice, DBA/2 mice also showed impaired LI and a different temporal profile in their responses to amphetamine and phencyclidine.

CONCLUSION

Relative to the C57BL/6 strain, DBA/2 mice displayed multiple behavioural traits relevant to schizophrenia psycho- and physiopathology, indicative of both dopaminergic and glutamatergic/N-methyl-D: -aspartic acid receptor dysfunctions. Further examination of their underlying neurobiological differences is therefore warranted in order to enhance the power of this specific inter-strain comparison as a model of schizophrenia.

Mood stabilizers increase prepulse inhibition in DBA/2NCrl mice

RATIONALE

Lithium and several antiepileptic drugs have mood-stabilizing effects in bipolar disorder and schizophrenia. Both disorders are characterized by deficits in prepulse inhibition (PPI) of the acoustic startle response.

OBJECTIVES

Using the DBA/2 model of naturally low PPI, which is reliably increased by antipsychotics, five mood stabilizers in clinical use were tested to determine whether they would also increase PPI in this model. All drugs were administered intraperitoneally (i.p.) 30 min before testing.

RESULTS

Lithium chloride (30 mg/kg), topiramate (100 and 300 mg/kg), carbamazepine (30, 60, and 100 mg/kg), valproic acid (178 and 316 mg/kg), and lamotrigine (3, 10, and 30 mg/kg) increased percent PPI. The antiepileptic drugs carbamazepine, valproic acid, and lamotrigine at high doses also decreased no-stimulus amplitudes and increased startle amplitudes. At high doses of carbamazepine, valproic acid, and lamotrigine, increases in percent PPI were independent of the increases in startle amplitude.

CONCLUSIONS

The demonstrated efficacy of five mood stabilizers in the DBA/2 model of naturally low PPI points to the translational value of this model in predicting therapeutic activity in schizophrenia and bipolar disorder of compounds with diverse mechanisms of action.

Interactions between the glycine transporter 1(GlyT1) inhibitor SSR504734 and psychoactive drugs in mouse motor behaviour

The specific glycine transporter 1 (GlyT1) inhibitor, SSR504734, is highly effective in enhancing N-methyl-D-aspartate receptor (NMDAR) function by elevating the availability of the NMDAR co-agonist, glycine, in the vicinity of NMDAR-containing glutamatergic synapses. According to the glutamatergic hypofunction hypothesis of schizophrenia, SSR504734 may therefore possess antipsychotic potential. Here, we evaluated the effects of SSR504734 in response to three psychomimetic drugs: phencyclidine, amphetamine, and apomorphine in male C57BL/6 mice. SSR504734 attenuated phencyclidine-induced (5 mg/kg, i.p.) hyperlocomotion, but potentiated the motor stimulant and motor depressant effects of amphetamine (2.5 mg/kg, i.p.) and apomorphine (0.75 mg/kg, s.c.), respectively. Hence, SSR504734 not only confers resistance to NMDAR blockade, but also enhances the locomotor response to dopaminergic stimulation. The latter finding adds to reports that SSR504734 may modulate dopamine-mediated behaviour by interference with normal glutamate-dopamine interaction. The specificity of this action of SSR504734 will be highly relevant to its potential application as an antipsychotic agent.

Sensorimotor gating in neurotensin-1 receptor null mice

BACKGROUND

Converging evidence has implicated endogenous neurotensin (NT) in the pathophysiology of brain processes relevant to schizophrenia. Prepulse inhibition of the startle reflex (PPI) is a measure of sensorimotor gating and considered to be of strong relevance to neuropsychiatric disorders associated with psychosis and cognitive dysfunction. Mice genetically engineered to not express NT display deficits in PPI that model the PPI deficits seen in schizophrenia patients. NT1 receptors have been most strongly implicated in mediating the psychosis relevant effects of NT such as attenuating PPI deficits. To investigate the role of NT1 receptors in the regulation of PPI, we measured baseline PPI in wildtype (WT) and NT1 knockout (KO) mice. We also tested the effects of amphetamine and dizocilpine, a dopamine agonist and NMDA antagonist, respectively, that reduce PPI as well as the NT1 selective receptor agonist PD149163, known to increase PPI in rats.

METHODS

Baseline PPI and acoustic startle response were measured in WT and NT1 KO mice. After baseline testing, mice were tested again after receiving intraperatoneal (IP) saline or one of three doses of amphetamine (1.0, 3.0 and 10.0 mg/kg), dizocilpine (0.3, 1.0 and 3.0 mg/kg) and PD149163 (0.5, 2.0 and 6.0 mg/kg) on separate test days.

RESULTS

Baseline PPI and acoustic startle response in NT1 KO mice were not significantly different from NT1 WT mice. WT and KO mice exhibited similar responses to the PPI-disrupting effects of dizocilpine and amphetamine. PD149163 significantly facilitated PPI (P < 0.004) and decreased the acoustic startle response (P < 0.001) in WT but not NT1 KO mice.

CONCLUSIONS

The data does not support the regulation of baseline PPI or the PPI disruptive effects of amphetamine or dizocilpine by endogenous NT acting at the NT1 receptor, although they support the antipsychotic potential of pharmacological activation of NT1 receptors by NT1 agonists.

Pro-cognitive and antipsychotic efficacy of the alpha7 nicotinic partial agonist SSR180711 in pharmacological and neurodevelopmental latent inhibition models of schizophrenia

Schizophrenia symptoms can be segregated into positive, negative and cognitive, which exhibit differential sensitivity to drug treatments. Accumulating evidence points to efficacy of alpha7 nicotinic receptor (nAChR) agonists for cognitive deficits in schizophrenia but their activity against positive symptoms is thought to be minimal. The present study examined potential pro-cognitive and antipsychotic activity of the novel selective alpha7 nAChR partial agonist SSR180711 using the latent inhibition (LI) model. LI is the reduced efficacy of a previously non-reinforced stimulus to gain behavioral control when paired with reinforcement, compared with a novel stimulus. Here, no-drug controls displayed LI if non-reinforced pre-exposure to a tone was followed by weak but not strong conditioning (2 vs 5 tone-shock pairings). MK801 (0.05 mg/kg, i.p.) -treated rats as well as rats neonatally treated with nitric oxide synthase inhibitor L-NoArg (10 mg/kg, s.c.) on postnatal days 4-5, persisted in displaying LI with strong conditioning, whereas amphetamine (1 mg/kg) -treated rats failed to show LI with weak conditioning. SSR180711 (0.3, 1, 3 mg/kg, i.p.) was able to alleviate abnormally persistent LI produced by acute MK801 and neonatal L-NoArg; these models are believed to model cognitive aspects of schizophrenia and activity here was consistent with previous findings with alpha7-nAChR agonists. In addition, unexpectedly, SSR180711 (1, 3 mg/kg, i.p.) potentiated LI with strong conditioning in no-drug controls and reversed amphetamine-induced LI disruption, two effects considered predictive of activity against positive symptoms of schizophrenia. These findings suggest that SSR180711 may be beneficial not only for the treatment of cognitive symptoms in schizophrenia, as reported multiple times previously, but also positive symptoms.

Dopaminergic hypofunctions and prepulse inhibition deficits in mice lacking midkine

Midkine is a 13-kDa retinoic acid-induced heparin-binding growth factor involved in various biological phenomena such as cell migration, neurogenesis, and tissue repair. We previously demonstrated that midkine-deficient (Mdk(-/-)) mice exhibited a delayed hippocampal development with impaired working memory and increased anxiety only at the age of 4 weeks. To assess whether midkine gene could play important roles in development and maintenance of central nervous system, we investigated biochemical and behavioral parameters in dopamine and glutamate neurotransmission of Mdk(-/-) mice. The Mdk(-/-) mice exhibited a hypodopaminergic state (i.e., decreased levels of dopamine and its receptors in the striatum) with no alterations of glutamatergic system (i.e., normal level of glutamate, glutamine, glycine, d-serine, l-serine, and NMDA receptors in the frontal cortex and hippocampus). We also found prepulse inhibition deficits reversed by clozapine and haloperidol in the Mdk(-/-) mice. Our results suggested that midkine deficiency may be related to neurochemical and behavioral dysfunctions in dopaminergic system.

Using the MATRICS to guide development of a preclinical cognitive test battery for research in schizophrenia

Cognitive deficits in schizophrenia are among the core symptoms of the disease, correlate with functional outcome, and are not well treated with current antipsychotic therapies. In order to bring together academic, industrial, and governmental bodies to address this great 'unmet therapeutic need', the NIMH sponsored the Measurement and Treatment Research to Improve Cognition in Schizophrenia (MATRICS) initiative. Through careful factor analysis and consensus of expert opinion, MATRICS identified seven domains of cognition that are deficient in schizophrenia (attention/vigilance, working memory, reasoning and problem solving, processing speed, visual learning and memory, verbal learning and memory, and social cognition) and recommended a specific neuropsychological test battery to probe these domains. In order to move the field forward and outline an approach for translational research, there is a need for a "preclinical MATRICS" to develop a rodent test battery that is appropriate for drug development. In this review, we outline such an approach and review current rodent tasks that target these seven domains of cognition. The rodent tasks are discussed in terms of their validity for probing each cognitive domain as well as a brief overview of the pharmacology and manipulations relevant to schizophrenia for each task.

Developing translational animal models for symptoms of schizophrenia or bipolar mania

Animal models have long been used to explore hypotheses regarding the neurobiological substrates of and treatments for psychiatric disorders. Early attempts to develop models that mimic the entirety of the diagnostic syndromes in psychiatry have evolved into more appropriate efforts to model specific symptoms. Such an approach reflects the facts that even in patients, clinical symptoms transcend diagnostic categories, and the specific etiologies of psychiatric disorders are unknown. An animal model can only be identified adequately by specifying both the manipulation (drug, lesion, strain) used to induce abnormalities and the measure(s) used to characterize them. A wide range of pharmacological, lesion, and developmental manipulations have been combined with various measures of information processing to develop useful animal models that parallel human tests. Prepulse inhibition of startle, event-related potential (ERP) measures of auditory gating, and Cambridge neuropsychological test automated battery (CANTAB) measures of cognition are examples of measures that can be used in both rodents and humans and that are robustly altered in both psychiatric disorders and animals manipulated with appropriate drugs or lesions. The further development of cross-species models is critically important, given the new opportunities for the development and registration of specific treatments for the cognitive disorders of schizophrenia that are not ameliorated by available drugs. In moving beyond the focus on psychotic symptoms to the cognitive symptoms of schizophrenia, animal models that do not involve manipulations of dopamine D(2) receptors but that do utilize information processing measures that are correlated with cognitive disturbances are receiving increased attention. Here, selected examples of how cross-species measures of psychiatric disorders are developed and validated are discussed. Specific animal paradigms that parallel the specific domains of cognition that are altered in schizophrenia provide one focus of the review. Another focus includes efforts to develop new human models of psychiatric symptoms that are designed to parallel existing tests used in rodents.

Short-term selective breeding for high and low prepulse inhibition of the acoustic startle response; pharmacological characterization and QTL mapping in the selected lines

Selective breeding offers several important advantages over using inbred strain panels in detecting genetically correlated traits to the selection phenotype. The purpose of the current study was to selectively breed for prepulse inhibition (PPI) of the acoustic startle response (ASR), to pharmacologically and behaviorally characterize the selected lines and to use the lines for quantitative trait loci (QTL) mapping. Starting with heterogeneous stock mice formed by crossing the C57BL/6J, DBA/2J, BALB/cJ and LP/J inbred strains and using a short-term selective breeding strategy, animals were selected for High and Low PPI. The selection phenotype was the 80 dB prepulse tone (15 dB above the background noise). After five generations of selection, the High and Low lines differed significantly (78.1 +/- 3.1 vs. 45.2 +/- 3.9 [percent inhibition], p < 0.00001). The effects of haloperidol and MK-801 on PPI were not different between the High and Low lines. However, at the highest dose tested (10 mg/kg), the High line was more sensitive than the Low line to the disruptive PPI effects of methamphetamine. The lines did not differ in terms of basal activity or methamphetamine-induced changes in locomotor activity. The High and Low lines were genotyped using a panel of 768 SNPs. Significant QTLs (LOD > 10) were detected on chromosomes 11 and 16 that appeared similar to those detected previously [Hitzemann, R., Bell, J., Rasmussen, E., McCaughran, J. Mapping the genes for the acoustic startle response (ASR) and prepulse inhibition of the ASR in the BXD recombinant inbred series: effect of high-frequency hearing loss and cochlear pathology. In: Willott JF, editor. Handbook of mouse auditory research: From behavior to molecular biology. New York: CRC Press; 2001, p. 441-455.; Petryshen, T. L, Kirby, A., Hammer, R.P. Jr, Purcell, S., O'Leary, S.B., Singer, J.B., et al. Two quantitative trait loci for prepulse inhibition of startle identified on mouse chromosome 16 using chromosome substitution strains. Genetics 2005; 171: 1895-1904.]. Overall, the current study illustrates that the heritability of PPI is sufficient for shortterm selective breeding and that the lines which are developed can be used to characterize the factors associated with the regulation of PPI.

Nicotine and nicotinic system in hypoglutamatergic models of schizophrenia

Schizophrenia is a complex neuropsychiatric disorder with devastating consequences. It is characterized by thought fragmentation, hallucination and delusion, collectively referred to as positive symptoms. In addition, mood changes or affective disorders, referred to as negative symptoms, as well as cognitive impairments can be manifested in these patients. Arguably, modeling such a disorder in its entirety in animals might not be feasible. Despite this limitation, various models with significant construct, predictive and some face validity have been developed. One such model, based on hypoglutamatergic hypothesis of schizophrenia, makes use of administering NMDA receptor antagonists and evaluating behavioral paradigms such as sensorimotor gating. Because of very high incidence of smoking among schizophrenic patients, it has been postulated that some of these patients may actually be self medicating with tobacco's nicotine. Research on nicotinic-glutamatergic interactions using various animal models has yielded conflicting results. In this review, some of these models and possible confounding factors are discussed. Overall, a therapeutic potential for nicotinic agonists in schizophrenia can be suggested. Moreover, it is evident that various experimental paradigms or models of schizophrenia symptoms need to be combined to provide a wider spectrum of the behavioral phenotype, as each model has its inherent limitations.

Altered hippocampal circuit function in C3H alpha7 null mutant heterozygous mice

The alpha7 subtype of nicotinic receptor is highly expressed in the hippocampus where it is purported to modulate release of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA). The alpha7 receptor-mediated release of GABA is thought to contribute to hippocampal inhibition (gating) of response to repetitive auditory stimulation. This hypothesis is supported by observations of hippocampal auditory gating deficits in mouse strains with low levels of hippocampal alpha7 receptors compared to strains with high levels of hippocampal alpha7 receptors. The difficulty with comparisons between mouse strains, however, is that different strains have different genetic backgrounds. Thus, the observed interstrain differences in hippocampal auditory gating might result from factors other than interstrain variations in the density of hippocampal alpha7 receptors. To address this issue, hippocampal binding of the alpha7 receptor-selective antagonist alpha-bungarotoxin as well as hippocampal auditory gating characteristics were compared in C3H wild type and C3H alpha7 receptor null mutant heterozygous mice. The C3H alpha7 heterozygous mice exhibited significant reductions in hippocampal alpha7 receptor levels and abnormal hippocampal auditory gating compared to the C3H wild type mice. In addition, a general increase in CA3 pyramidal neuron responsivity was observed in the heterozygous mice compared to the wild type mice. These data suggest that decreasing hippocampal alpha7 receptor density results in a profound alteration in hippocampal circuit function.