Neuregulin 1 hypomorphic mutant mice: enhanced baseline locomotor activity but normal psychotropic drug-induced hyperlocomotion and prepulse inhibition regulation

Impaired extinction of operant cocaine in a genetic mouse model of schizophrenia risk

BACKGROUND

Individuals with schizophrenia have high rates of comorbid substance use problems. One potential explanation for this comorbidity is similar neuropathophysiology in substance use and schizophrenia, which may arise from shared genetic risk factors between the two disorders. Here we investigated if genetic risk for schizophrenia could affect drug reward and reinforcement for cocaine in an established mouse model of genetic risk for schizophrenia, the neuregulin 1 transmembrane domain heterozygous (Nrg1 TM HET) mouse.

METHODS

We examined drug-induced locomotor sensitization and conditioned place preference for several cocaine doses (5, 10, 20, 30 mg/kg) in male adult Nrg1 TM HET and wild-type-like (WT) littermates. We also investigated intravenous self-administration of and motivation for cocaine (doses 0.1, 0.5, 1 mg/kg/infusion), as well as extinction and cue-induced reinstatement of cocaine. In a follow-up experiment, we examined self-administration, extinction and cue-induced reinstatement of a natural reward, oral sucrose.

RESULTS

Cocaine preference was similar between Nrg1 TM HET mice and WT littermates at all doses tested. Locomotor sensitization to cocaine was not affected by Nrg1 genotype at any dose. Although self-administration and motivation for cocaine was unaffected, extinction of cocaine self-administration was impaired in Nrg1 TM HET compared to WT controls, and cue-induced reinstatement was greater in Nrg1 mutants in the middle of the reinstatement session. Sucrose self-administration and extinction thereof was not affected by genotype, but inactive lever responding was elevated during cue-induced reinstatement for operant sucrose in Nrg1 TM HET mice compared to WTs.

DISCUSSION

These results suggest impaired response inhibition for cocaine in Nrg1 TM HET mice and suggests Nrg1 mutation may contribute to behaviours which can limit control over cocaine use.

Methamphetamine-induced locomotor sensitization in mice is not associated with deficits in a range of cognitive, affective and social behaviours: interaction with brain-derived neurotrophic factor Val66Met genotype

Chronic methamphetamine (Meth) abuse may induce psychosis similar to that observed in schizophrenia. Brain-derived neurotrophic factor (BDNF) has been implicated in the development of psychosis. We have previously shown long-term protein expression changes in mice treated chronically with Meth depending on BDNF Val66Met genotype. The aim of this study was to investigate if these protein expression changes were associated with differential changes in a range of behavioural paradigms for cognition, anxiety, social and other behaviours. Male and female Val/Val, Val/Met and Met/Met mice were treated with an escalating Meth dose protocol from 6 to 9 weeks of age, with controls receiving saline injections. Several overlapping cohorts were tested in the Y-maze for short-term spatial memory, novel-object recognition test, context and cued fear conditioning, sociability and social preference, elevated plus maze for anxiety-like behaviour and prepulse inhibition (PPI) of acoustic startle. Finally, the animals were assessed for spontaneous exploratory locomotor activity and acute Meth-induced locomotor hyperactivity. Acute Meth caused significantly greater locomotor hyperactivity in mice previously treated with the drug than in saline-pretreated controls. Meth-pretreated female mice showed a mild increase in spontaneous locomotor activity. There were no Meth-induced deficits in any of the other behavioural tests. Val/Met mice showed higher overall social investigation time and lower PPI compared with the Val/Val genotype independent of pretreatment. These results show limited long-term effects of chronic Meth on a range of cognitive, affective and social behaviours despite marked drug-induced locomotor sensitization in mice. There was no interaction with BDNF Val66Met genotype.

Current advancements of modelling schizophrenia using patient-derived induced pluripotent stem cells

Schizophrenia (SZ) is a severe psychiatric disorder, with a prevalence of 1-2% world-wide and substantial health- and social care costs. The pathology is influenced by both genetic and environmental factors, however the underlying cause still remains elusive. SZ has symptoms including delusions, hallucinations, confused thoughts, diminished emotional responses, social withdrawal and anhedonia. The onset of psychosis is usually in late adolescence or early adulthood. Multiple genome-wide association and whole exome sequencing studies have provided extraordinary insights into the genetic variants underlying familial as well as polygenic forms of the disease. Nonetheless, a major limitation in schizophrenia research remains the lack of clinically relevant animal models, which in turn hampers the development of novel effective therapies for the patients. The emergence of human induced pluripotent stem cell (hiPSC) technology has allowed researchers to work with SZ patient-derived neuronal and glial cell types in vitro and to investigate the molecular basis of the disorder in a human neuronal context. In this review, we summarise findings from available studies using hiPSC-based neural models and discuss how these have provided new insights into molecular and cellular pathways of SZ. Further, we highlight different examples of how these models have shown alterations in neurogenesis, neuronal maturation, neuronal connectivity and synaptic impairment as well as mitochondrial dysfunction and dysregulation of miRNAs in SZ patient-derived cultures compared to controls. We discuss the pros and cons of these models and describe the potential of using such models for deciphering the contribution of specific human neural cell types to the development of the disease.

The effects of preventative cannabidiol in a male neuregulin 1 mouse model of schizophrenia

Cannabidiol (CBD) is a non-intoxicating cannabinoid with antipsychotic-like properties, however it’s potential to prevent schizophrenia development has not been thoroughly investigated. Brain maturation during adolescence creates a window where CBD could potentially limit the development of schizophrenia. The neuregulin 1 transmembrane domain heterozygous (Nrg1 TM HET) mutant mouse shows face, predictive, and construct validity for schizophrenia. Here we sought to determine if CBD given in adolescence could prevent the development of the schizophrenia-relevant phenotype, as well as susceptibility to the psychoactive cannabinoid Δ⁹-tetrahydrocannabinol (THC) in Nrg1 TM HET mice. Adolescent male Nrg1 mutants and wild type-like (WT) animals were administered 30 mg/kg CBD i.p. daily for seven weeks, and were tested for locomotion, social behavior, sensorimotor gating and cognition, and sensitivity to acute THC-induced behaviors. GAD67, GluA1, and NMDAR1 protein levels were measured in the hippocampus, striatum, and prefrontal cortex. Chronic adolescent CBD increased locomotion in animals regardless of genotype, was anxiolytic, and increased social behavior when animals were tested for their acute THC response. CBD did not alleviate the schizophrenia-relevant hyperlocomotive phenotype of Nrg1 mutants, nor deficits in social behaviors. Nrg1 mutant mice treated with CBD and THC showed no habituation to a startle pulse, suggesting CBD increased vulnerability to the startle habituation-reducing effects of THC in mutant mice. CBD increased levels of GluA1, but reduced levels of GAD67 in the hippocampus of Nrg1 mutants. These results suggest adolescent CBD is not effective as a preventative of schizophrenia-relevant behavioral deficits in mutants and may actually contribute to pathological changes in the brain that increase sensitivity to THC in particular behavioral domains.

Role of the NRG1/ErbB4 and PI3K/AKT/mTOR signaling pathways in the anti-psychotic effects of aripiprazole and sertindole in ketamine-induced schizophrenia-like behaviors in rats

Schizophrenia is a common mental disorder affecting patients' thoughts, behavior, and cognition. Recently, the NRG1/ErbB4 signaling pathway emerged as a candidate therapeutic target for schizophrenia. This study investigates the effects of aripiprazole and sertindole on the NRG1/ErbB4 and PI3K/AKT/mTOR signaling pathways in ketamine-induced schizophrenia in rats. Young male Wistar rats received ketamine (30 mg/kg, intraperitoneally) for 5 consecutive days and aripiprazole (3 mg/kg, orally) or sertindole (2.5 mg/kg, orally) for 14 days. The proposed pathway was investigated by injecting LY294002 (a selective PI3K inhibitor) (25 μg/kg, intrahippocampal injection) 30 min before the drugs. Twenty-four hours after the last injection, animals were subjected to behavioral tests: the open field test, sucrose preference test, novel object recognition task, and social interaction test. Both aripiprazole and sertindole significantly ameliorated ketamine-induced schizophrenic-like behavior, as expected, because of their previously demonstrated antipsychotic activity. Besides, both drugs alleviated ketamine-induced oxidative stress and neurotransmitter level changes in the hippocampus. They also increased the gamma-aminobutyric acid and glutamate levels and glutamate decarboxylase 67 and parvalbumin mRNA expression in the hippocampus. Moreover, aripiprazole and sertindole increased the NRG1 and ErbB4 mRNA expression levels and PI3K, p-Akt, and mTOR protein expression levels. Interestingly, pre-injecting LY294002 abolished all the effects of the drugs. This study reveals that the antipsychotic effects of aripiprazole and sertindole are partly due to oxidative stress reduction as well as NRG1/ErbB4 and PI3K/AKT/mTOR signaling pathways activation. The NRG1/ErbB4 and PI3K signaling pathways may offer a new therapeutic approach for treating schizophrenia in humans.

Repeated administration of N-ethyl-pentedrone induces increased aggression and impairs social exploration after withdrawal in mice

N-ethyl-pentedrone (NEPD, 2-(ethylamino)-1-phenyl-1-pentanone) is one of the latest synthetic cathinone derivatives that emerged into the illicit drug market. This drug has psychostimulant properties and has been related with several intoxications and even fatalities. However, information about the consequences of its acute and repeated consumption is lacking. Thus, the aim of our study was to investigate the behavioral effects after both acute and repeated NEPD exposure as well as the neurochemical changes. Male OF1 mice were treated with an acute dose (1, 3 or 10 mg/kg, i.p.) or received repeated injections of these doses (twice/day, 5 days) of NEPD. Shortly after drug-exposure or during drug-withdrawal, anxiety-like behavior, aggressiveness, social interaction, depressive-like symptoms, body weight and temperature were assessed. Also, monoamine synthesis enzymes, levels of neurotransmitters and their precursors and main metabolites, as well as ΔFosB, were determined in striatum and prefrontal cortex from post-mortem tissue. Acute administration of NEPD induced anxiolytic effects and reduced social exploration whereas during withdrawal after repeated administration the anxiolytic effect had vanished, and the reduced social exploration was still present and accompanied with increased aggressive behavior. Moreover, NEPD (10 mg/kg) induced slight hyperthermia and reduced weight gain during the repeated administration, whereas increased locomotor activity and lack of depressive symptoms were found during withdrawal. This was accompanied by increased plasma corticosterone and decrease in striatal dopamine. Finally, the long-lasting and robust increase in ΔFosB levels found in striatum after NEPD chronic exposure suggests a high risk of dependence. The increased aggressivity and locomotor activity, together with this potential of inducing dependence justify a warning about the risks of consumption of NEPD if translated to humans.

Orexin deficiency affects sensorimotor gating and its amphetamine-induced impairment

The orexin neuropeptides have an important role in the regulation of the sleep/wake cycle and foraging, as well as in reward processing and emotions. Furthermore, recent research implicates the orexin system in different behavioral endophenotypes of neuropsychiatric diseases such as social avoidance and cognitive flexibility. Utilizing orexin-deficient mice, the present study tested the hypothesis that orexin is involved in two further mouse behavioral endophenotypes of neuropsychiatric disorders, i.e., sensorimotor gating and amphetamine sensitivity. The data revealed that orexin-deficient mice expressed a deficit in sensorimotor gating, measured by prepulse inhibition of the startle response. Amphetamine treatment impaired prepulse inhibition in wildtype and heterozygous orexin-deficient mice, but had no effects in homozygous orexin-deficient mice. Furthermore, locomotor activity and center time in the open field was not affected by orexin deficiency but was similarly increased or decreased, respectively, by amphetamine treatment in all genotypes. These data indicate that the orexin system modulates prepulse inhibition and is involved in mediating amphetamine's effect on prepulse inhibition. Future studies should investigate whether pharmacological manipulations of the orexin system can be used to treat neuropsychiatric diseases associated with deficits in sensorimotor gating, such as schizophrenia or attention deficit hyperactivity disorder.

Sex Differences in Psychosis: Focus on Animal Models

Most psychiatric illnesses, such as schizophrenia, show profound sex differences in incidence, clinical presentation, course, and outcome. Fortunately, more recently the literature on sex differences and (to a lesser extent) effects of sex steroid hormones is expanding, and in this review we have focused on such studies in psychosis, both from a clinical/epidemiological and preclinical/animal model perspective. We begin by briefly describing the clinical evidence for sex differences in schizophrenia epidemiology, symptomatology, and pathophysiology. We then detail sex differences and sex hormone effects in behavioral animal models of psychosis, specifically psychotropic drug-induced locomotor hyperactivity and disruption of prepulse inhibition. We expand on the preclinical data to include developmental and genetic models of psychosis, such as the maternal immune activation model and neuregulin transgenic animals, respectively. Finally, we suggest several recommendations for future studies, in order to facilitate a better understanding of sex differences in the development of psychosis.

The behavioural phenotype of 14-month-old female TAU58/2 transgenic mice

Frontotemporal dementia (FTD) and Alzheimer's disease (AD) exhibit intracellular inclusions [neurofibrillary tangles (NFT's)] of microtubule-associated protein tau that contributes to neuronal dysfunction and death. Mutations in the microtubule-associated protein tau (MAPT) gene leads to tau hyperphosphorylation and promotes NFT formation. The TAU58/2 transgenic mouse model expresses mutant human tau (P301S mutation) and exhibits behavioural abnormalities relevant to dementia in early adulthood. Here we comprehensively determined the behavioural phenotype of TAU58/2 transgenic female mice at 14 months of age using test paradigms relevant to FTD and AD. TAU58/2 females showed a significant motor deficit and lower bodyweight compared to WT littermates. Transgenic females failed to habituate to the test arena in the light-dark test. Interestingly, transgenics did not exhibit an anxiolytic-like phenotype and intermediate-term spatial learning in the cheeseboard test was intact. However, a significant learning deficit was detected in the 1st trial across test days indicating impaired long-term spatial memory. In addition, the preference for a previously rewarded location was absent in transgenic females during probe trial testing. Finally, TAU58/2 mice had a defective acoustic startle response and impaired sensorimotor gating. In conclusion TAU58/2 mice exhibit several behavioural deficits that resemble those observed in human FTD and AD. Additionally, we observed a novel startle response deficit in these mice. At 14 months of age, TAU58/2 females represent a later disease stage and are therefore a potentially useful model to test efficacy of therapeutics to reverse or ameliorate behavioural deficits in post-onset tauopapthy-related neurodegenerative disorders.

Resveratrol ameliorates the effect of maternal immune activation associated with schizophrenia in adulthood offspring

Maternal exposure to infectious agents such as arboviruses, bacteria, or other protozoans has been associated with an elevated risk of schizophrenia (SZ). Evidence suggests that immunological processes occurring during infection may disturb the neural progenitor, impacting the central nervous system (CNS) functions. Moreover, growing evidence suggests that resveratrol (RSV) has neuroprotective activity through anti-oxidant and anti-inflammatory mechanisms. Therefore, we investigated if the treatment with RSV during pregnancy would prevent the abnormalities associated with a SZ-like phenotype induced by maternal immune activation (MIA). Pregnant dams stimulated with a subcutaneous (s.c.) injection of polyriboinosinic-polyribocytidylic acid (poly I:C; 50 mg/kg), a viral nucleic acid mimetic or vehicle, on gestational day (GD) 12.5, were treated with RSV (40 mg/kg, s.c.) or saline, from GD 9.5 to GD 14.5. On day 45 after birth, the offspring was evaluated using a three-compartment social interaction test, elevated plus maze, and hyperlocomotion test induced by amphetamine. After the behavioral tests, the relative expression of mRNA to synapsin 1 (Syn1), oligodendrocyte transcription factor 1 (Olig1), and SRY (sex-determining region Y)-box 2 (Sox2) was determined in the hippocampus and cortex. Treatment with RSV restored the social behavior and attenuated the hyperlocomotion of the offspring bred by dams submitted to MIA. RSV prevented the effects of MIA on Syn1 and Olig1 expression in the hippocampus and Syn1 in the cortex. The present study showed that maternal treatment with RSV attenuates some of the negative behavioral impacts caused by MIA, with modulation of synaptic and oligodendrogenesis processes.

Contribution of CB2 receptors in schizophrenia-related symptoms in various animal models: Short review

Schizophrenia is a severe and chronic mental disease with a high prevalence and a variety of symptoms. Data from behavioural studies suggest that it is rational to investigate the endocannabinoid system (ECS) and its cannabinoid receptor (CBr) because they seem to underlie susceptibility to schizophrenia, and these findings have pointed to several lines of future research. Currently, most available studies address the role of CBr type 1 in schizophrenia-like responses. Here, we present for the first time, a review that demonstrates the pivotal role of CBr type 2 in the regulation of neurobiological processes underlying cognition, psychosis- and mood-related (anxiety, depression) behaviours, all of which may be included in schizophrenia symptoms. This review is based on available evidence from the PubMed database regarding schizophrenia-like symptoms induced via CB2r modulation in various animal models. The data presented in this manuscript indicate that CB2r could be a promising new key target in the treatment of different central nervous system (CNS) disorders, which manifest as psychosis, mood-related disturbances and/or memory impairment.

Antidepressant-like effects of ketamine in a mouse model of serotonergic dysfunction

Traditional monoaminergic treatments of depression frequently exhibit suboptimal tolerability and effectiveness. The 'short' (s) allele variant of 5-HTTLPR is known to compromise transcriptional efficacy of the serotonin transporter (5-HTT) and can reduce treatment response to traditional antidepressants (e.g. selective serotonin reuptake inhibitors or SSRIs). This study sought to establish the 5-HTT knock-out (KO) line as a mouse model of SSRI-resistant depression and assess its response to a novel glutamatergic antidepressant, ketamine, a non-competitive N-methyl-d-aspartate receptor (NMDAR) antagonist. Following acute antidepressant treatment, 5-HTT KO mice and wild-type (WT) controls were subjected to the forced-swim test (FST), one of the most widely used techniques to detect acute antidepressant response. As hypothesised, when assessed 30 min after administration in the FST, the SSRI sertraline (20 mg/kg, i.p.) produced antidepressant-like effects in WT control but not in 5-HTT KO mice. In contrast, ketamine (20 mg/kg, i.p.) induced antidepressant-like effects in both genotypes. 5-HTT KO mice also exhibited a reduced locomotor response to both MK-801 (another NMDAR antagonist) and ketamine, and reduced GluN2A protein levels in the hippocampus, suggesting glutamatergic dysfunction in this model. These results highlight the utility of 5-HTT KO mice as a relevant model of SSRI-resistant depression and demonstrate that ketamine can produce acute antidepressant-like effects in conditions of 5-HTT deficiency. These findings extend existing literature that indicates ketamine is effective in ameliorating symptoms of treatment-resistant depression and may have implications for understanding the cellular and molecular mechanisms underlying the antidepressant effects of ketamine. This article is part of the special issue entitled 'Serotonin Research: Crossing Scales and Boundaries'.

Map2k7 Haploinsufficiency Induces Brain Imaging Endophenotypes and Behavioral Phenotypes Relevant to Schizophrenia

c-Jun N-terminal kinase (JNK) signaling contributes to functional plasticity in the brain and cognition. Accumulating evidence implicates a role for MAP kinase kinase 7 (MAP2K7), a JNK activator encoded by the Map2k7 gene, and other JNK pathway components in schizophrenia (ScZ). Mice haploinsufficient for Map2k7 (Map2k7+/- mice) display ScZ-relevant cognitive deficits, although the mechanisms are unclear. Here we show that Map2k7+/- mice display translationally relevant alterations in brain function, including hippocampal and mesolimbic system hypermetabolism with a contrasting prefrontal cortex (PFC) hypometabolism, reminiscent of patients with ScZ. In addition Map2k7+/- mice show alterations in functional brain network connectivity paralleling those reported in early ScZ, including PFC and hippocampal hyperconnectivity and compromised mesolimbic system functional connectivity. We also show that although the cerebral metabolic response to ketamine is preserved, the response to dextroamphetamine (d-amphetamine) is significantly attenuated in Map2k7+/- mice, supporting monoamine neurotransmitter system dysfunction but not glutamate/NMDA receptor (NMDA-R) dysfunction as a consequence of Map2k7 haploinsufficiency. These effects are mirrored behaviorally with an attenuated impact of d-amphetamine on sensorimotor gating and locomotion, whereas similar deficits produced by ketamine are preserved, in Map2k7+/- mice. In addition, Map2k7+/- mice show a basal hyperactivity and sensorimotor gating deficit. Overall, these data suggest that Map2k7 modifies brain and monoamine neurotransmitter system function in a manner relevant to the positive and cognitive symptoms of ScZ.

The maternal immune activation model uncovers a role for the Arx gene in GABAergic dysfunction in schizophrenia

A hallmark feature of schizophrenia is altered high frequency neural oscillations, including reduced auditory-evoked gamma oscillatory power, which is underpinned by parvalbumin (PV) interneuron dysfunction. Maternal immune activation (MIA) in rodents models an environmental risk factor for schizophrenia and recapitulates these PV interneuron changes. This study sought to link reduced PV expression in the MIA model with alterations to auditory-evoked gamma oscillations and transcript expression. We further aligned transcriptional findings from the animal model with human genome sequencing data. We show that MIA, induced by the viral mimetic, poly-I:C in C57Bl/6 mice, caused in adult offspring reduced auditory-evoked gamma and theta oscillatory power paralleled by reduced PV protein levels. We then showed the Arx gene, critical to healthy neurodevelopment of PV interneurons, is reduced in the forebrain of MIA exposed mice. Finally, in a whole-genome sequenced patient cohort, we identified a novel missense mutation of ARX in a patient with schizophrenia and in the Psychiatric Genomics Consortium 2 cohort, a nominal association of proximal ARX SNPs with the disorder. This suggests MIA, as a risk factor for schizophrenia, may be influencing Arx expression to induce the GABAergic dysfunction seen in schizophrenia and that the ARX gene may play a role in the prenatal origins of schizophrenia pathophysiology.

First behavioural assessment of a novel Immp2l knockdown mouse model with relevance for Gilles de la Tourette syndrome and Autism spectrum disorder

Gilles de la Tourette syndrome (GTS) is a neurodevelopmental disorder, which shares some clinical features with Autism spectrum disorder (ASD). The genetic factors relevant to the development of both disorders are yet to be fully understood, however, some genetic association studies have identified inner mitochondrial membrane peptidase subunit 2 (IMMP2L) as a potential risk gene for both GTS and ASD. The impact of Immp2l deficiency on behavioural domains is currently unknown. A new genetic mouse model for Immp2l was developed. Adult heterozygous (HET) and homozygous (HOMO) Immp2l knockdown (Immp2l KD) mice of both sexes were compared to wild type-like (WT) littermates in the open field (OF), social interaction, novel object recognition, marble burying, and prepulse inhibition (PPI). The effect of acute dexamphetamine (2 mg/kg) on OF behaviour was also determined. OF locomotion was significantly higher in HET compared to HOMO male littermates. Male and female HOMO mice were much more sensitive to the locomotor-stimulating effects of dexamphetamine (DEX), whereas only HOMO males exhibited significant increased DEX-induced OF exploration compared to control groups. HOMO females failed to habituate to an acoustic startle stimulus. Furthermore, compared to HOMO females, HET females showed reduced social interaction, and a similar trend was seen in HET males. The Immp2l KD mouse model possesses moderate face validity for preclinical research into GTS and ASD, in particular as dysfunctional dopaminergic neurotransmission appears to be one mechanism leading to disease presentation. The sex-dependent differences observed in most findings reinforce the strong influence of sex in the pathophysiology of GTS and ASD.

Interaction of Brain-Derived Neurotrophic Factor Val66Met genotype and history of stress in regulation of prepulse inhibition in mice

The Brain-Derived Neurotrophic Factor (BDNF) Val66Met polymorphism results in reduced activity-dependent BDNF release and has been implicated in schizophrenia. However, effects of the polymorphism on functional dopaminergic and N-methyl-d-aspartate (NMDA) receptor-associated activity remain unclear. We used prepulse inhibition, a measure of sensorimotor gating which is disrupted in schizophrenia, and assessed the effects of acute treatment with the dopamine receptor agonist, apomorphine (APO), and the NMDA receptor antagonist, MK-801. We used adult humanized hBDNF^Val66Met 'knockin' mice which express either the Val/Val, Val/Met or Met/Met genotype. An interaction of BDNF with stress was modelled by chronic young-adult treatment with corticosterone (CORT). At 1 or 3mg/kg, APO had no effect in Val/Val mice but significantly reduced PPI at the 100ms inter-stimulus interval (ISI) in Val/Met and Met/Met mice. However, after CORT pretreatment, APO significantly reduced PPI in all genotypes similarly. At 0.1 or 0.25mg/kg, MK-801 significantly disrupted PPI at the 100ms ISI independent of genotype or CORT pretreatment. There were differential effects of APO and MK-801 on PPI at the 30ms ISI and startle between the genotypes, irrespective of CORT pretreatment. These results show that the BDNF Val66Met Val/Met and Met/Met genotypes are more sensitive than the Val/Val genotype to the effect of APO on PPI. A history of stress, here modelled by chronic CORT administration, increases effects of APO in Val/Val mice.

Sensorimotor gating deficits and effects of antipsychotics on the hyperactivity in VGF-overexpressing mice

BACKGROUND

VGF nerve growth factor inducible (VGF) is a neuropeptide which is expressed in neuronal cells and endocrine cells. VGF is induced by several neurotrophic factors. The expression level of VGF in patients with schizophrenia is increased in cerebrospinal fluid (CSF) and prefrontal cortex. In our previous study, we generated mice in which the expression level of VGF in the brain was increased. VGF-overexpressing mice exhibited abnormal behaviors including hyperactivity. However, it remains unknown whether VGF-overexpressing mice exhibit the endophenotype of schizophrenia and whether abnormal behaviors in these mice can be improved by antipsychotics.

METHODS

In the present study, we investigated schizophrenia-like behaviors and the responsiveness to antipsychotics in transgenic mice.

RESULTS

VGF-overexpressing mice (1) exhibited prepulse inhibition (PPI) impairment, (2) showed normalized hyperactivity following antipsychotic drug treatment, and (3) showed abnormal responsiveness to haloperidol.

CONCLUSION

Upregulation of VGF may be implicated in the pathophysiology of schizophrenia and abnormalities of dopaminergic signaling.

Selective enhancement of NMDA receptor-mediated locomotor hyperactivity by male sex hormones in mice

RATIONALE

Altered glutamate NMDA receptor function is implicated in schizophrenia, and gender differences have been demonstrated in this illness.

OBJECTIVES

This study aimed to investigate the interaction of gonadal hormones with NMDA receptor-mediated locomotor hyperactivity and PPI disruption in mice.

RESULTS

The effect of 0.25 mg/kg of MK-801 on locomotor activity was greater in male mice than in female mice. Gonadectomy (by surgical castration) significantly reduced MK-801-induced hyperlocomotion in male mice, but no effect of gonadectomy was seen in female mice or on amphetamine-induced locomotor hyperactivity. The effect of MK-801 on prepulse inhibition of startle (PPI) was similar in intact and castrated male mice and in ovariectomized (OVX) female mice. In contrast, there was no effect of MK-801 on PPI in intact female mice. Forebrain NMDA receptor density, as measured with [³H]MK-801 autoradiography, was significantly higher in male than in female mice but was not significantly altered by either castration or OVX.

CONCLUSIONS

These results suggest that male sex hormones enhance the effect of NMDA receptor blockade on psychosis-like behaviour. This interaction was not seen in female mice and was independent of NMDA receptor density in the forebrain. Male sex hormones may be involved in psychosis by an interaction with NMDA receptor hypofunction.

Specialized Information Processing Deficits and Distinct Metabolomic Profiles Following TM-Domain Disruption of Nrg1

Although there is considerable genetic and pathologic evidence for an association between neuregulin 1 (NRG1) dysregulation and schizophrenia, the underlying molecular and cellular mechanisms remain unclear. Mutant mice containing disruption of the transmembrane (TM) domain of the NRG1 gene constitute a heuristic model for dysregulation of NRG1-ErbB4 signaling in schizophrenia. The present study focused on hitherto uncharacterized information processing phenotypes in this mutant line. Using a mass spectrometry-based metabolomics approach, we also quantified levels of unique metabolites in brain. Across 2 different sites and protocols, Nrg1 mutants demonstrated deficits in prepulse inhibition, a measure of sensorimotor gating, that is, disrupted in schizophrenia; these deficits were partially reversed by acute treatment with second, but not first-, generation antipsychotic drugs. However, Nrg1 mutants did not show a specific deficit in latent inhibition, a measure of selective attention that is also disrupted in schizophrenia. In contrast, in a "what-where-when" object recognition memory task, Nrg1 mutants displayed sex-specific (males only) disruption of "what-when" performance, indicative of impaired temporal aspects of episodic memory. Differential metabolomic profiling revealed that these behavioral phenotypes were accompanied, most prominently, by alterations in lipid metabolism pathways. This study is the first to associate these novel physiological mechanisms, previously independently identified as being abnormal in schizophrenia, with disruption of NRG1 function. These data suggest novel mechanisms by which compromised neuregulin function from birth might lead to schizophrenia-relevant behavioral changes in adulthood.

Behavioral abnormalities with disruption of brain structure in mice overexpressing VGF

VGF nerve growth factor inducible (VGF) is a neuropeptide induced by nerve growth factor and brain-derived neurotrophic factor. This peptide is involved in synaptic plasticity, neurogenesis, and neurite growth in the brain. Patients with depression and bipolar disorder have lower-than-normal levels of VGF, whereas patients with schizophrenia and other cohorts of patients with depression have higher-than-normal levels. VGF knockout mice display behavioral abnormalities such as higher depressive behavior and memory dysfunction. However, it is unclear whether upregulation of VGF affects brain function. In the present study, we generated mice that overexpress VGF and investigated several behavioral phenotypes and the brain structure. These adult VGF-overexpressing mice showed (a) hyperactivity, working memory impairment, a higher depressive state, and lower sociality compared with wild-type mice; (b) lower brain weight without a change in body weight; (c) increased lateral ventricle volume compared with wild-type mice; and (d) striatal morphological defects. These results suggest that VGF may modulate a variety of behaviors and brain development. This transgenic mouse line may provide a useful model for research on mental illnesses.

First Behavioural Characterisation of a Knockout Mouse Model for the Transforming Growth Factor (TGF)-β Superfamily Cytokine, MIC-1/GDF15

Macrophage inhibitory cytokine-1 (MIC-1), also known as growth differentiation factor 15 (GDF15), is a stress response cytokine. MIC-1/GDF15 is secreted into the cerebrospinal fluid and increased levels of MIC-1/GDF15 are associated with a variety of diseases including cognitive decline. Furthermore, Mic-1/Gdf15 knockout mice (Mic-1 KO) weigh more, have increased adiposity, associated with increased spontaneous food intake, and exhibit reduced basal energy expenditure and physical activity. The current study was designed to comprehensively determine the role of MIC-1/GDF15 on behavioural domains of male and female knockout mice including locomotion, exploration, anxiety, cognition, social behaviours, and sensorimotor gating. Mic-1 KO mice exhibited a task-dependent increase in locomotion and exploration and reduced anxiety-related behaviours across tests. Spatial working memory and social behaviours were not affected by Mic-1/Gdf15 deficiency. Interestingly, knockout mice formed an increased association with the conditioned stimulus in fear conditioning testing and also displayed significantly improved prepulse inhibition. Overall sex effects were evident for social behaviours, fear conditioning, and sensorimotor gating. This is the first study defining the role of Mic-1/Gdf15 in a number of behavioural domains. Whether the observed impact is based on direct actions of Mic-1/Gdf15 deficiency on the CNS or whether the behavioural effects are mediated by indirect actions on e.g. other neurotransmitter systems must be clarified in future studies.

Gene × Environment Interactions in Schizophrenia: Evidence from Genetic Mouse Models

The study of gene × environment, as well as epistatic interactions in schizophrenia, has provided important insight into the complex etiopathologic basis of schizophrenia. It has also increased our understanding of the role of susceptibility genes in the disorder and is an important consideration as we seek to translate genetic advances into novel antipsychotic treatment targets. This review summarises data arising from research involving the modelling of gene × environment interactions in schizophrenia using preclinical genetic models. Evidence for synergistic effects on the expression of schizophrenia-relevant endophenotypes will be discussed. It is proposed that valid and multifactorial preclinical models are important tools for identifying critical areas, as well as underlying mechanisms, of convergence of genetic and environmental risk factors, and their interaction in schizophrenia.

14-3-3ζ deficient mice in the BALB/c background display behavioural and anatomical defects associated with neurodevelopmental disorders

Sequencing and expression analyses implicate 14-3-3ζ as a genetic risk factor for neurodevelopmental disorders such as schizophrenia and autism. In support of this notion, we recently found that 14-3-3ζ^−/− mice in the Sv/129 background display schizophrenia-like defects. As epistatic interactions play a significant role in disease pathogenesis we generated a new congenic strain in the BALB/c background to determine the impact of genetic interactions on the 14-3-3ζ^−/− phenotype. In addition to replicating defects such as aberrant mossy fibre connectivity and impaired spatial memory, our analysis of 14-3-3ζ^−/− BALB/c mice identified enlarged lateral ventricles, reduced synaptic density and ectopically positioned pyramidal neurons in all subfields of the hippocampus. In contrast to our previous analyses, 14-3-3ζ^−/− BALB/c mice lacked locomotor hyperactivity that was underscored by normal levels of the dopamine transporter (DAT) and dopamine signalling. Taken together, our results demonstrate that dysfunction of 14-3-3ζ gives rise to many of the pathological hallmarks associated with the human condition. 14-3-3ζ-deficient BALB/c mice therefore provide a novel model to address the underlying biology of structural defects affecting the hippocampus and ventricle, and cognitive defects such as hippocampal-dependent learning and memory.

Neuregulin 1 expression and electrophysiological abnormalities in the Neuregulin 1 transmembrane domain heterozygous mutant mouse

Background

The Neuregulin 1 transmembrane domain heterozygous mutant (Nrg1 TM HET) mouse is used to investigate the role of Nrg1 in brain function and schizophrenia-like behavioural phenotypes. However, the molecular alterations in brain Nrg1 expression that underpin the behavioural observations have been assumed, but not directly determined. Here we comprehensively characterise mRNA Nrg1 transcripts throughout development of the Nrg1 TM HET mouse. In addition, we investigate the regulation of high-frequency (gamma) electrophysiological oscillations in this mutant mouse to associate molecular changes in Nrg1 with a schizophrenia-relevant neurophysiological profile.

Methods

Using exonic probes spanning the cysteine-rich, epidermal growth factor (EGF)-like, transmembrane and intracellular domain encoding regions of Nrg1, mRNA levels were measured using qPCR in hippocampus and frontal cortex from male and female Nrg1 TM HET and wild type-like (WT) mice throughout development. We also performed electrophysiological recordings in adult mice and analysed gamma oscillatory at baseline, in responses to auditory stimuli and to ketamine.

Results

In both hippocampus and cortex, Nrg1 TM HET mice show significantly reduced expression of the exon encoding the transmembrane domain of Nrg1 compared with WT, but unaltered mRNA expression encoding the extracellular bioactive EGF-like and the cysteine-rich (type III) domains, and development-specific and region-specific reductions in the mRNA encoding the intracellular domain. Hippocampal Nrg1 protein expression was not altered, but NMDA receptor NR2B subunit phosphorylation was lower in Nrg1 TM HET mice. We identified elevated ongoing and reduced sensory-evoked gamma power in Nrg1 TM HET mice.

Interpretation

We found no evidence to support the claim that the Nrg1 TM HET mouse represents a simple haploinsufficient model. Further research is required to explore the possibility that mutation results in a gain of Nrg1 function.

Partial genetic deletion of neuregulin 1 modulates the effects of stress on sensorimotor gating, dendritic morphology, and HPA axis activity in adolescent mice

Stress has been linked to the pathogenesis of schizophrenia. Genetic variation in neuregulin 1 (NRG1) increases the risk of developing schizophrenia and may help predict which high-risk individuals will transition to psychosis. NRG1 also modulates sensorimotor gating, a schizophrenia endophenotype. We used an animal model to demonstrate that partial genetic deletion of Nrg1 interacts with stress to promote neurobehavioral deficits of relevance to schizophrenia. Nrg1 heterozygous (HET) mice displayed greater acute stress-induced anxiety-related behavior than wild-type (WT) mice. Repeated stress in adolescence disrupted the normal development of higher prepulse inhibition of startle selectively in Nrg1 HET mice but not in WT mice. Further, repeated stress increased dendritic spine density in pyramidal neurons of the medial prefrontal cortex (mPFC) selectively in Nrg1 HET mice. Partial genetic deletion of Nrg1 also modulated the adaptive response of the hypothalamic-pituitary-adrenal axis to repeated stress, with Nrg1 HET displaying a reduced repeated stress-induced level of plasma corticosterone than WT mice. Our results demonstrate that Nrg1 confers vulnerability to repeated stress-induced sensorimotor gating deficits, dendritic spine growth in the mPFC, and an abberant endocrine response in adolescence.

Phenotypic effects of maternal immune activation and early postnatal milieu in mice mutant for the schizophrenia risk gene neuregulin-1

Risk of schizophrenia is likely to involve gene × environment (G × E) interactions. Neuregulin 1 (NRG1) is a schizophrenia risk gene, hence any interaction with environmental adversity, such as maternal infection, may provide further insights into the basis of the disease. This study examined the individual and combined effects of prenatal immune activation with polyriboinosinic-polyribocytidilic acid (Poly I:C) and disruption of the schizophrenia risk gene NRG1 on the expression of behavioral phenotypes related to schizophrenia. NRG1 heterozygous (NRG1 HET) mutant breeding pairs were time-mated. Pregnant dams received a single injection (5mg/kg i.p.) of Poly I:C or vehicle on gestation day 9 (GD9). Offspring were then cross-fostered to vehicle-treated or Poly I:C-treated dams. Expression of schizophrenia-related behavioral endophenotypes was assessed at adolescence and in adulthood. Combining NRG1 disruption and prenatal environmental insult (Poly I:C) caused developmental stage-specific deficits in social behavior, spatial working memory and prepulse inhibition (PPI). However, combining Poly I:C and cross-fostering produced a number of behavioral deficits in the open field, social behavior and PPI. This became more complex by combining NRG1 deletion with both Poly I:C exposure and cross-fostering, which had a robust effect on PPI. These findings suggest that concepts of G × E interaction in risk of schizophrenia should be elaborated to multiple interactions that involve individual genes interacting with diverse biological and psychosocial environmental factors over early life, to differentially influence particular domains of psychopathology, sometimes over specific stages of development.

Distinct phenotypes of new transmembrane-domain neuregulin 1 mutant mice and the rescue effects of valproate on the observed schizophrenia-related cognitive deficits

Accumulating evidence suggests that neuregulin 1 (NRG1) might be involved in the neurodevelopment, neural plasticity, GABAergic neurotransmission, and pathogenesis of schizophrenia. NRG1 is abundantly expressed in the hippocampus, and emerging studies have begun to reveal the link between NRG1 signaling and cognitive deficits in schizophrenic patients. Because the transmembrane domain of NRG1 is vital for both forward and reverse signaling cascades, new Nrg1-deficient mice that carry a truncation of the transmembrane domain of the Nrg1 gene were characterized and used in this study to test a NRG1 loss-of-function hypothesis for schizophrenia. Both male and female Nrg1 heterozygous mutant mice and their wild-type littermates were used in a series of 4 experiments to characterize the impact of Nrg1 on behavioral phenotypes and to determine the importance of Nrg1 in the regulation of hippocampal neuromorphology and local GABAergic interneurons. First, a comprehensive battery of behavioral tasks indicated that male Nrg1-deficient mice exhibited significant impairments in cognitive functions. Second, pharmacological challenges were conducted and revealed that Nrg1 haploinsufficiency altered GABAergic activity in males. Third, although no genotype-specific neuromorphological alterations were found in the hippocampal CA1 pyramidal neurons, significant reductions in the hippocampal expressions of GAD67 and parvalbumin were revealed in the Nrg1-deficient males. Fourth, chronic treatment with valproate rescued the observed behavioral deficits and hippocampal GAD67 reduction in Nrg1-deficient males. Collectively, these results indicate the potential therapeutic effect of valproate and the importance of Nrg1 in the regulation of cognitive functions and hippocampal GABAergic interneurons, especially in males.

Locomotor hyperactivity in 14-3-3ζ KO mice is associated with dopamine transporter dysfunction

Dopamine (DA) neurotransmission requires a complex series of enzymatic reactions that are tightly linked to catecholamine exocytosis and receptor interactions on pre- and postsynaptic neurons. Regulation of dopaminergic signalling is primarily achieved through reuptake of extracellular DA by the DA transporter (DAT) on presynaptic neurons. Aberrant regulation of DA signalling, and in particular hyperactivation, has been proposed as a key insult in the presentation of schizophrenia and related neuropsychiatric disorders. We recently identified 14-3-3ζ as an essential component of neurodevelopment and a central risk factor in the schizophrenia protein interaction network. Our analysis of 14-3-3ζ-deficient mice now shows that baseline hyperactivity of knockout (KO) mice is rescued by the antipsychotic drug clozapine. 14-3-3ζ KO mice displayed enhanced locomotor hyperactivity induced by the DA releaser amphetamine. Consistent with 14-3-3ζ having a role in DA signalling, we found increased levels of DA in the striatum of 14-3-3ζ KO mice. Although 14-3-3ζ is proposed to modulate activity of the rate-limiting DA biosynthesis enzyme, tyrosine hydroxylase (TH), we were unable to identify any differences in total TH levels, TH localization or TH activation in 14-3-3ζ KO mice. Rather, our analysis identified significantly reduced levels of DAT in the absence of notable differences in RNA or protein levels of DA receptors D1-D5. Providing insight into the mechanisms by which 14-3-3ζ controls DAT stability, we found a physical association between 14-3-3ζ and DAT by co-immunoprecipitation. Taken together, our results identify a novel role for 14-3-3ζ in DA neurotransmission and provide support to the hyperdopaminergic basis of pathologies associated with schizophrenia and related disorders.

Neuregulin 1: a prime candidate for research into gene-environment interactions in schizophrenia? Insights from genetic rodent models

Schizophrenia is a multi-factorial disease characterized by a high heritability and environmental risk factors. In recent years, an increasing number of researchers worldwide have started investigating the “two-hit hypothesis” of schizophrenia predicting that genetic and environmental risk factors (GxE) interactively cause the development of the disorder. This work is starting to produce valuable new animal models and reveal novel insights into the pathophysiology of schizophrenia. This mini review will focus on recent advancements in the field made by challenging mutant and transgenic rodent models for the schizophrenia candidate gene neuregulin 1 (NRG1) with particular environmental factors. It will outline results obtained from mouse and rat models for various Nrg1 isoforms/isoform types (e.g., transmembrane domain Nrg1, Type II Nrg1), which have been exposed to different forms of stress (acute versus chronic, restraint versus social) and housing conditions (standard laboratory versus minimally enriched housing). These studies suggest Nrg1 as a prime candidate for GxE interactions in schizophrenia rodent models and that the use of rodent models will enable a better understanding of GxE interactions and the underlying mechanisms.

A neuregulin 1 transmembrane domain mutation causes imbalanced glutamatergic and dopaminergic receptor expression in mice

The neuregulin 1 gene has repeatedly been identified as a susceptibility gene for schizophrenia, thus mice with genetic mutations in this gene offer a valuable tool for studying the role of neuregulin 1 in schizophrenia-related neurotransmission. In this study, slide-based receptor autoradiography was used to quantify glutamatergic N-methyl-d-aspartate (NMDA), dopaminergic D2, cannabinoid CB1 and acetylcholine M1/4 receptor levels in the brains of male heterozygous transmembrane domain neuregulin 1 mutant (Nrg1(+/-)) mice at two ages. Mutant mice expressed small but significant increases in NMDA receptor levels in the cingulate cortex (7%, p=0.044), sensory cortex (8%, p=0.024), and motor cortex (8%, p=0.047), effects that were independent of age. In the nucleus accumbens and thalamus Nrg1(+/-) mice exhibited age-dependent alterations in NMDA receptors. Nrg1(+/-) mice showed a statistically significant increase in NMDA receptor levels in the nucleus accumbens of 14-week-old Nrg1(+/-) mice compared to control littermates of the same age (12%, p=0.026), an effect that was not seen in 20-week-old mice. In contrast, NMDA receptor levels in the thalamus, while initially unchanged in 14-week-old mice, were then decreased in the 20-week-old Nrg1(+/-) mice compared to control littermates of the same age (14%, p=0.011). Nrg1(+/-) mutant mice expressed a significant reduction in D2 receptor levels (13-16%) in the striatum compared to controls, independent of age. While there was a borderline significant increase (6%, p=0.058) in cannabinoid CB1 receptor levels in the substantia nigra of Nrg1(+/-) mice compared to controls, CB1 as well as acetylcholine M1/4 receptors showed no change in Nrg1(+/-) mice in any other brain region examined. These data indicate that a Nrg1 transmembrane mutation produces selective imbalances in glutamatergic and dopaminergic neurotransmission, which are two key systems believed to contribute to schizophrenia pathogenesis. While the effects on these systems are subtle, they may underlie the susceptibility of these mutants to further impacts.

BDNF deficiency and young-adult methamphetamine induce sex-specific effects on prepulse inhibition regulation

Brain-derived neurotrophic factor (BDNF) has been implicated in the pathophysiology of schizophrenia, yet its role in the development of specific symptoms is unclear. Methamphetamine (METH) users have an increased risk of psychosis and schizophrenia, and METH-treated animals have been used extensively as a model to study the positive symptoms of schizophrenia. We investigated whether METH treatment in BDNF heterozygous (HET) mutant mice has cumulative effects on sensorimotor gating, including the disruptive effects of psychotropic drugs. BDNF HETs and wildtype (WT) littermates were treated during young adulthood with METH and, following a 2-week break, prepulse inhibition (PPI) was examined. At baseline, BDNF HETs showed reduced PPI compared to WT mice irrespective of METH pre-treatment. An acute challenge with amphetamine (AMPH) disrupted PPI but male BDNF HETs were more sensitive to this effect, irrespective of METH pre-treatment. In contrast, female mice treated with METH were less sensitive to the disruptive effects of AMPH, and there were no effects of BDNF genotype. Similar changes were not observed in the response to an acute apomorphine (APO) or MK-801 challenge. These results show that genetically-induced reduction of BDNF caused changes in a behavioral endophenotype relevant to the positive symptoms of schizophrenia. However, major sex differences were observed in the effects of a psychotropic drug challenge on this behavior. These findings suggest sex differences in the effects of BDNF depletion and METH treatment on the monoamine signaling pathways that regulate PPI. Given that these same pathways are thought to contribute to the expression of positive symptoms in schizophrenia, this work suggests that there may be significant sex differences in the pathophysiology underlying these symptoms. Elucidating these sex differences may be important for our understanding of the neurobiology of schizophrenia and developing better treatments strategies for the disorder.

Genetic models of schizophrenia and related psychotic disorders: progress and pitfalls across the methodological "minefield"

The challenge of modelling a complex and multifaceted disorder such as schizophrenia is epitomised by the considerable degree of phenotypic variability described in patients and by the absence of specific and consistent neuropathological biomarkers. The pattern and severity of a range of clinical features, including florid psychotic symptoms such as hallucinations and delusions, negative symptoms and cognitive dysfunction, together with age at onset, course of illness and other indices, can vary greatly between individual patients. The undefined nature of the relationship between diagnosis and underlying aetiology has complicated research in the field of clinical and preclinical neuroscience, thereby making it difficult to generate or evaluate appropriate disease models of schizophrenia. In the present review, we explore those conceptual and practical issues that relate specifically to the genetic modelling of schizophrenia and related disorders in rodents. Practical issues that impact on the robustness of endophenotypic findings and their translational relevance are discussed with reference to evidence from selective genetic models of candidate risk genes and copy number variants implicated in schizophrenia.

Neuregulin-1 signalling and antipsychotic treatment: potential therapeutic targets in a schizophrenia candidate signalling pathway

Identifying the signalling pathways underlying the pathophysiology of schizophrenia is an essential step in the rational development of new antipsychotic drugs for this devastating disease. Evidence from genetic, transgenic and post-mortem studies have strongly supported neuregulin-1 (NRG1)-ErbB4 signalling as a schizophrenia susceptibility pathway. NRG1-ErbB4 signalling plays crucial roles in regulating neurodevelopment and neurotransmission, with implications for the pathophysiology of schizophrenia. Post-mortem studies have demonstrated altered NRG1-ErbB4 signalling in the brain of schizophrenia patients. Antipsychotic drugs have different effects on NRG1-ErbB4 signalling depending on treatment duration. Abnormal behaviours relevant to certain features of schizophrenia are displayed in NRG1/ErbB4 knockout mice or those with NRG1/ErbB4 over-expression, some of these abnormalities can be improved by antipsychotic treatment. NRG1-ErbB4 signalling has extensive interactions with the GABAergic, glutamatergic and dopaminergic neurotransmission systems that are involved in the pathophysiology of schizophrenia. These interactions provide a number of targets for the development of new antipsychotic drugs. Furthermore, the key interaction points between NRG1-ErbB4 signalling and other schizophrenia susceptibility genes may also potentially provide specific targets for new antipsychotic drugs. In general, identification of these targets in NRG1-ErbB4 signalling and interacting pathways will provide unique opportunities for the development of new generation antipsychotics with specific efficacy and fewer side effects.

What does a mouse tell us about neuregulin 1-cannabis interactions?

The link between cannabis and psychosis has been debated although there is substantial epidemiological evidence showing that cannabis increases the risk of psychosis. It has been hypothesized that schizophrenia patients carrying particular risk genes might be more sensitive to the psychosis-inducing effects of cannabis than other patients and healthy test subjects. Here we review the effects of cannabinoids on a mutant mouse model for the schizophrenia candidate gene neuregulin 1 (Nrg1). The studies suggest a complex interaction between cannabis and Nrg1: the neuro-behavioral effects of cannabinoids were different in Nrg1 mutant and control mice and depended on exposure time, sex, and age of test animals. This research provides the first evidence of complex cannabis-Nrg1 interactions suggesting Nrg1 as a prime target for future clinical investigations. Furthermore, it highlights that animal model research can broaden our understanding of the complex multi-factorial etiology of schizophrenia. Finally, the findings are important to preventive psychiatry: if the genes that confer genetic vulnerability to cannabis-induced psychosis were identified patients at-high risk could be forewarned of the potential dangers of cannabis abuse.

Novel behavioural characteristics of the APP(Swe)/PS1ΔE9 transgenic mouse model of Alzheimer's disease

In order to better understand animal models of Alzheimer's disease, novel phenotyping strategies have been established for transgenic mouse models. In line with this, the current study characterised male APPxPS1 transgenic mice on mixed C57BL/6JxC3H/HeJ background for the first time for social recognition memory, sensorimotor gating, and spatial memory using the cheeseboard test as an alternative to the Morris water maze. Furthermore, locomotion, anxiety, and fear conditioning were evaluated in transgenic and wild type-like animals. APPxPS1 males displayed task-dependent hyperlocomotion and anxiety behaviours and exhibited social recognition memory impairments compared to wild type-like littermates. Spatial learning and memory, fear conditioning, and sensorimotor gating were unaffected in APPxPS1 transgenic mice. In conclusion, this study describes for the first time social recognition memory deficits in male APPxPS1 mice and suggests that spatial learning and memory deficits reported in earlier studies are dependent on the sex and genetic background of the APPxPS1 mouse line used. Furthermore, particular test conditions of anxiety and spatial memory paradigms appear to impact on the behavioural response of this transgenic mouse model for Alzheimer's disease.

Transmembrane domain Nrg1 mutant mice show altered susceptibility to the neurobehavioural actions of repeated THC exposure in adolescence

Heavy cannabis abuse increases the risk of developing schizophrenia. Adolescents appear particularly vulnerable to the development of psychosis-like symptoms after cannabis use. To test whether the schizophrenia candidate gene neuregulin 1 (NRG1) modulates the effects of cannabinoids in adolescence, we tested male adolescent heterozygous transmembrane domain Nrg1 mutant (Nrg1 TM HET) mice and wild type-like littermates (WT) for their neurobehavioural response to repeated Δ(9)-tetrahydrocannabinol (THC, 10 mg/kg i.p. for 21 d starting on post-natal day 31). During treatment and 48 h after treatment withdrawal, we assessed several behavioural parameters relevant to schizophrenia. After behavioural testing we measured autoradiographic CB(1), 5-HT(2A) and NMDA receptor binding. The hyperlocomotor phenotype typical of Nrg1 mutants emerged after drug withdrawal and was more pronounced in vehicle than THC-treated Nrg1 TM HET mice. All mice were equally sensitive to THC-induced suppression of locomotion. However, mutant mice appeared protected against inhibiting effects of repeated THC on investigative social behaviours. Neither THC nor Nrg1 genotype altered prepulse inhibition. Repeated adolescent THC promoted differential effects on CB(1) and 5-HT(2A) receptor binding in the substantia nigra and insular cortex respectively, decreasing binding in WT while increasing it in Nrg1 TM HET mice. THC also selectively affected 5-HT(2A) receptor binding in several other regions in WT mice, whereas NMDA receptor binding was only affected in mutant mice. Overall, Nrg1 mutation does not appear to increase the induction of psychotomimetic symptoms by repeated adolescent THC exposure but may attenuate some of its actions on social behaviour and schizophrenia-relevant neurotransmitter receptor profiles.

Exploring the role of 5-HT1A receptors in the regulation of prepulse inhibition in mice: implications for cross-species comparisons

Prepulse inhibition (PPI) is a model of sensorimotor gating, a sensory filtering mechanism which is disrupted in schizophrenia. Here, investigation of the role of the serotonin-1A (5-HT(1A)) receptor in the regulation of PPI in two mouse strains, C57Bl/6 and Balb/c, was used to address findings in the PPI literature on species and mouse strain differences that question the usefulness of PPI as a cross-species preclinical test. Although the full 5-HT(1A) receptor agonist, 8-OH-DPAT, induced markedly different strain-specific responses in PPI, other selective 5-HT(1A) receptor ligands with partial agonist or antagonist activity elicited similar effects across strains. Pretreatment with the serotonin precursor, 5-HTP, to increase serotonergic activity in the brain, unmasked a decrease in PPI caused by 8-OH-DPAT in C57Bl/6 mice. Pretreatment with the serotonin synthesis inhibitor, PCPA, to decrease serotonergic activity in the brain, unmasked an 8-OH-DPAT-induced increase in PPI in this strain. These studies show that the strain-dependent involvement of 5-HT(1A) receptors in PPI can be modulated by the type of 5-HT(1A) ligand used, or increasing or decreasing serotonin levels in the brain. These results help to clarify some of the mouse strain and species differences in PPI regulation and strengthen its usefulness as a cross-species measure of sensorimotor gating.

Estudos traducionais de neuropsiquiatria e esquizofrenia: modelos animais genéticos e de neurodesenvolvimento

Sintomas psiquiátricos são subjetivos por natureza e tendem a se sobrepor entre diferentes desordens. Sendo assim, a criação de modelos de uma desordem neuropsiquiátrica encontra desafios pela falta de conhecimento dos fundamentos da fisiopatologia e diagnósticos precisos. Modelos animais são usados para testar hipóteses de etiologia e para representar a condição humana tão próximo quanto possível para aumentar nosso entendimento da doença e avaliar novos alvos para a descoberta de drogas. Nesta revisão, modelos animais genéticos e de neurodesenvolvimento de esquizofrenia são discutidos com respeito a achados comportamentais e neurofisiológicos e sua associação com a condição clínica. Somente modelos animais específicos de esquizofrenia podem, em último caso, levar a novas abordagens diagnósticas e descoberta de drogas. Argumentamos que biomarcadores moleculares são importantes para aumentar a tradução de animais a humanos, já que faltam a especificidade e a fidelidade necessárias às leituras comportamentais para avaliar sintomas psiquiátricos humanos.