Risperidone pretreatment prevents elevated locomotor activity following neonatal hippocampal lesions

Animal Models of Relevance to the Schizophrenia Prodrome

Patients with schizophrenia often undergo a prodromal phase prior to diagnosis. Given the absence of significant therapeutic improvements, attention has recently shifted to the possibility of intervention during this early stage to delay or diminish symptom severity or even prevent onset. Unfortunately, the 20 or so trials of intervention to date have not been successful in either preventing onset or improving long-term outcomes in subjects who are at risk of developing schizophrenia. One reason may be that the biological pathways an effective intervention must target are not static. The prodromal phase typically occurs during late adolescence, a period during which a number of brain circuits and structures are still maturing. We propose that developing a deeper understanding of which circuits/processes and brain structures are still maturing at this time and which processes drive the transition to schizophrenia will take us a step closer to developing better prophylactic interventions. Fortunately, such knowledge is now emerging from clinical studies, complemented by work in animal models. Our task here is to describe what would constitute an appropriate animal model to study and to potentially intervene in such processes. Such a model would allow invasive analysis of the cellular and molecular substrates of the progressive neurobiology that defines the schizophrenia prodrome and hopefully offer valuable insights into potential prophylactic targets.

Deficient DNA base-excision repair in the forebrain leads to a sex-specific anxiety-like phenotype in mice

Background

Neuropsychiatric disorders, such as schizophrenia (SZ) and autism spectrum disorder (ASD), are common, multi-factorial and multi-symptomatic disorders. Ample evidence implicates oxidative stress, deficient repair of oxidative DNA lesions and DNA damage in the development of these disorders. However, it remains unclear whether insufficient DNA repair and resulting DNA damage are causally connected to their aetiopathology, or if increased levels of DNA damage observed in patient tissues merely accumulate as a consequence of cellular dysfunction. To assess a potential causal role for deficient DNA repair in the development of these disorders, we behaviourally characterized a mouse model in which CaMKIIa-Cre-driven postnatal conditional knockout (KO) of the core base-excision repair (BER) protein XRCC1 leads to accumulation of unrepaired DNA damage in the forebrain.

Results

CaMKIIa-Cre expression caused specific deletion of XRCC1 in the dorsal dentate gyrus (DG), CA1 and CA2 and the amygdala and led to increased DNA damage therein. While motor coordination, cognition and social behaviour remained unchanged, XRCC1 KO in the forebrain caused increased anxiety-like behaviour in males, but not females, as assessed by the light–dark box and open field tests. Conversely, in females but not males, XRCC1 KO caused an increase in learned fear-related behaviour in a cued (Pavlovian) fear conditioning test and a contextual fear extinction test. The relative density of the GABA(A) receptor alpha 5 subunit (GABRA5) was reduced in the amygdala and the dorsal CA1 in XRCC1 KO females, whereas male XRCC1 KO animals exhibited a significant reduction of GABRA5 density in the CA3. Finally, assessment of fast-spiking, parvalbumin-positive (PV) GABAergic interneurons revealed a significant increase in the density of PV+ cells in the DG of male XRCC1 KO mice, while females remained unchanged.

Conclusions

Our results suggest that accumulation of unrepaired DNA damage in the forebrain alters the GABAergic neurotransmitter system and causes behavioural deficits in relation to innate and learned anxiety in a sex-dependent manner. Moreover, the data uncover a previously unappreciated connection between BER deficiency, unrepaired DNA damage in the hippocampus and a sex-specific anxiety-like phenotype with implications for the aetiology and therapy of neuropsychiatric disorders.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-022-01377-1.

The prefrontal cortex as a target for atypical antipsychotics in schizophrenia, lessons of neurodevelopmental animal models

Prefrontal cortex (PFC) inflammatory imbalance, oxidative/nitrosative stress (O/NS) and impaired neuroplasticity in schizophrenia are thought to have neurodevelopmental origins. Animal models are not only useful to test this hypothesis, they are also effective to establish a relationship among brain disturbances and behavior with the atypical antipsychotics (AAPs) effects. Here we review data of PFC post-mortem and in vivo neuroimaging, human induced pluripotent stem cells (hiPSC), and peripheral blood studies of inflammatory, O/NS, and neuroplasticity alterations in the disease as well as about their modulation by AAPs. Moreover, we reviewed the PFC alterations and the AAP mechanisms beyond their canonical antipsychotic action in four neurodevelopmental animal models relevant to the study of schizophrenia with a distinct approach in the generation of schizophrenia-like phenotypes, but all converge in O/NS and altered neuroplasticity in the PFC. These animal models not only reinforce the neurodevelopmental risk factor model of schizophrenia but also arouse some novel potential therapeutic targets for the disease including the reestablishment of the antioxidant response by the perineuronal nets (PNNs) and the nuclear factor erythroid 2-related factor (Nrf2) pathway, as well as the dendritic spine dynamics in the PFC pyramidal cells.

Preclinical validation of the micropipette-guided drug administration (MDA) method in the maternal immune activation model of neurodevelopmental disorders

Pharmacological treatments in laboratory rodents remain a cornerstone of preclinical psychopharmacological research and drug development. There are numerous ways in which acute or chronic pharmacological treatments can be implemented, with each method having certain advantages and drawbacks. Here, we describe and validate a novel treatment method in mice, which we refer to as the micropipette-guided drug administration (MDA) procedure. This administration method is based on a sweetened condensed milk solution as a vehicle for pharmacological substances, which motivates the animals to consume vehicle and/or drug solutions voluntarily in the presence of the experimenter. In a proof-of-concept study, we show that the pharmacokinetic profiles of the atypical antipsychotic drug, risperidone, were similar whether administered via the MDA procedure or via the conventional oral gavage method. Unlike the latter, however, MDA did not induce the stress hormone, corticosterone. Furthermore, we assessed the suitability and validity of the MDA method in a mouse model of maternal immune activation, which is frequently used as a model of immune-mediated neurodevelopmental disorders. Using this model, we found that chronic treatment (>4 weeks, once per day) with risperidone via MDA led to a dose-dependent mitigation of MIA-induced social interaction deficits and amphetamine hypersensitivity. Taken together, the MDA procedure described herein represents a novel pharmacological administration method for per os treatments in mice that is easy to implement, cost effective, non-invasive, and less stressful for the animals than conventional oral gavage methods.

Adolescence as a period of vulnerability and intervention in schizophrenia: Insights from the MAM model

Adolescence is a time of extensive neuroanatomical, functional and chemical reorganization of the brain, which parallels substantial maturational changes in behavior and cognition. Environmental factors that impinge on the timing of these developmental factors, including stress and drug exposure, increase the risk for psychiatric disorders. Indeed, antecedents to affective and psychotic disorders, which have clinical and pathophysiological overlap, are commonly associated with risk factors during adolescence that predispose to these disorders. In the context of schizophrenia, psychosis typically begins in late adolescence/early adulthood, which has been replicated by animal models. Rats exposed during gestational day (GD) 17 to the mitotoxin methylazoxymethanol acetate (MAM) exhibit behavioral, pharmacological, and anatomical characteristics consistent with an animal model of schizophrenia. Here we provide an overview of adolescent changes within the dopamine system and the PFC and review recent findings regarding the effects of stress and cannabis exposure during the peripubertal period as risk factors for the emergence of schizophrenia-like deficits. Finally, we discuss peripubertal interventions appearing to circumvent the emergence of adult schizophrenia-like deficits.

Developmental timing and critical windows for the treatment of psychiatric disorders

There is a growing understanding that pathological genetic variation and environmental insults during sensitive periods in brain development have long-term consequences on brain function, which range from learning disabilities to complex psychiatric disorders such as schizophrenia. Furthermore, recent experiments in animal models suggest that therapeutic interventions during sensitive periods, typically before the onset of clear neurological and behavioral symptoms, might prevent or ameliorate the development of specific pathologies. These studies suggest that understanding the dynamic nature of the pathophysiological mechanisms underlying psychiatric disorders is crucial for the development of effective therapies. In this Perspective, I explore the emerging concept of developmental windows in psychiatric disorders, their relevance for understanding disease progression and their potential for the design of new therapies. The limitations and caveats of early interventions in psychiatric disorders are also discussed in this context.

Peripubertal exposure to environmental enrichment prevents schizophrenia-like behaviors in the SHR strain animal model

Schizophrenia is a highly disabling mental disorder, in which genetics and environmental factors interact culminating in the disease. The treatment of negative symptoms and cognitive deficits with antipsychotics is currently inefficient and is an important field of research. Environmental enrichment (EE) has been suggested to improve some cognitive deficits in animal models of various psychiatric disorders. In this study, we aimed to evaluate a possible beneficial effect of early and long-term exposure to EE on an animal model of schizophrenia, the SHR strain. Young male Wistar rats (control strain) and SHRs (21 post-natal days) were housed for 6weeks in two different conditions: in large cages (10 animals per cage) containing objects of different textures, forms, colors and materials that were changed 3 times/week (EE condition) or in standard cages (5 animals per cage - Control condition). Behavioral evaluations - social interaction (SI), locomotion, prepulse inhibition of startle (PPI) and spontaneous alternation (SA) - were performed 6weeks after the end of EE. SHRs presented deficits in PPI (a sensorimotor impairment), SI (mimicking the negative symptoms) and SA (a working memory deficit), and also hyperlocomotion (modeling the positive symptoms). EE was able to reduce locomotion and increase PPI in both strains, and to prevent the working memory deficit in SHRs. EE also increased the number of neurons in the CA1 and CA3 of the hippocampus. In conclusion, EE can be a potential nonpharmacological strategy to prevent some behavioral deficits associated with schizophrenia.

Neural changes induced by antipsychotic administration in adolescence: A review of studies in laboratory rodents

Adolescence is characterized by major remodelling processes in the brain. Use of antipsychotic drugs (APDs) in adolescents has increased dramatically in the last 20 years; however, our understanding of the neurobiological consequences of APD treatment on the adolescent brain has not kept the same pace and significant concerns have been raised. In this review, we examined currently available preclinical studies of the effects of APDs on the adolescent brain. In animal models of neuropsychiatric disorders, adolescent APD treatment appears to be protective against selected structural, behavioural and neurochemical phenotypes. In "neurodevelopmentally normal" adolescent animals, a range of short- and long-term alterations in behaviour and neurochemistry have been reported. In particular, the adolescent brain appears to be sensitive to long-term locomotor/reward effects of chronic atypical APDs in contrast with the outcomes in adults. Long-lasting changes in dopaminergic, glutamatergic and gamma-amino butyric acid-ergic systems induced by adolescent APD administration have been observed in the nucleus accumbens. A detailed examination of other potential target regions such as striatum, prefrontal cortex and ventral tegmental area is still required. Through identification of specific neural pathways targeted by adolescent APD treatment, future studies will expand the current knowledge on long-term neural outcomes which are of translational value.

Altering the course of schizophrenia: progress and perspectives

Despite a lack of recent progress in the treatment of schizophrenia, our understanding of its genetic and environmental causes has considerably improved, and their relationship to aberrant patterns of neurodevelopment has become clearer. This raises the possibility that 'disease-modifying' strategies could alter the course to - and of - this debilitating disorder, rather than simply alleviating symptoms. A promising window for course-altering intervention is around the time of the first episode of psychosis, especially in young people at risk of transition to schizophrenia. Indeed, studies performed in both individuals at risk of developing schizophrenia and rodent models for schizophrenia suggest that pre-diagnostic pharmacotherapy and psychosocial or cognitive-behavioural interventions can delay or moderate the emergence of psychosis. Of particular interest are 'hybrid' strategies that both relieve presenting symptoms and reduce the risk of transition to schizophrenia or another psychiatric disorder. This Review aims to provide a broad-based consideration of the challenges and opportunities inherent in efforts to alter the course of schizophrenia.

Maturation- and sex-sensitive depression of hippocampal excitatory transmission in a rat schizophrenia model

Schizophrenia is associated with behavioral and brain structural abnormalities, of which the hippocampus appears to be one of the most consistent region affected. Previous studies performed on the poly I:C model of schizophrenia suggest that alterations in hippocampal synaptic transmission and plasticity take place in the offspring. However, these investigations yielded conflicting results and the neurophysiological alterations responsible for these deficits are still unclear. Here we performed for the first time a longitudinal study examining the impact of prenatal poly I:C treatment and of gender on hippocampal excitatory neurotransmission. In addition, we examined the potential preventive/curative effects of risperidone (RIS) treatment during the peri-adolescence period. Excitatory synaptic transmission was determined by stimulating Schaffer collaterals and monitoring fiber volley amplitude and slope of field-EPSP (fEPSP) in CA1 pyramidal neurons in male and female offspring hippocampal slices from postnatal days (PNDs) 18-20, 34, 70 and 90. Depression of hippocampal excitatory transmission appeared at juvenile age in male offspring of the poly I:C group, while it expressed with a delay in female, manifesting at adulthood. In addition, a reduced hippocampal size was found in both adult male and female offspring of poly I:C treated dams. Treatment with RIS at the peri-adolescence period fully restored in males but partly repaired in females these deficiencies. A maturation- and sex-dependent decrease in hippocampal excitatory transmission occurs in the offspring of poly I:C treated pregnant mothers. Pharmacological intervention with RIS during peri-adolescence can cure in a gender-sensitive fashion early occurring hippocampal synaptic deficits.

Posterior cerebellar vermal deficits in bipolar disorder

BACKGROUND

Based on growing evidence of the crucial role of the cerebellum in emotional regulation, we sought to identify cerebellar structural deficits in a large sample of patients with bipolar disorder (BD).

METHODS

Cerebellar gray matter density was examined in 49 BD patients (24 medication-naive and 25 medication-treated) and 50 carefully matched healthy individuals, using voxel-based morphometry with a high-resolution spatially unbiased atlas template of the human cerebellum. This recently developed methodology is specifically optimized for the assessment of cerebellar structures. We further explored whether antimanic treatment could attenuate cerebellar structural deficits.

RESULTS

BD patients showed a greater reduction in gray matter density of the posterior cerebellar regions, including the bilateral vermi and the right crus relative to healthy individuals (corrected p<.05). A stepwise linear reduction in gray matter density was observed in bilateral vermal regions between healthy individuals, medication-treated, and medication-naive BD patients. Furthermore, positive correlations of longer duration of illness with bilateral vermal gray matter deficits were observed only in medication-naive BD patients, but not in patients with medication history.

LIMITATIONS

This study adopted a cross-sectional design. The automatic intensity-normalization method for the measurement of cerebellar gray matter density may have a limitation in providing detailed anatomical information at a cerebellar folia level.

CONCLUSIONS

The current findings suggest that BD-related deficits in the posterior cerebellar regions, which appear to progress over the course of illness, could potentially be ameliorated by proper treatment with mood stabilizers.

Olanzapine treatment of adolescent rats alters adult reward behaviour and nucleus accumbens function

Antipsychotic drugs are increasingly used in children and adolescents to treat a variety of psychiatric disorders. However, little is known about the long-term effects of early life antipsychotic drug (APD) treatment. Most APDs are potent antagonists or partial agonists of dopamine (DA) D₂ receptors; atypical APDs also have multiple serotonergic activities. DA and serotonin regulate many neurodevelopmental processes. Thus, early life APD treatment can, potentially, perturb these processes, causing long-term behavioural and neurobiological sequelae. We treated adolescent, male rats with olanzapine (Ola) on post-natal days 28-49, under dosing conditions that approximate those employed therapeutically in humans. As adults, they exhibited enhanced conditioned place preference for amphetamine, as compared to vehicle-treated rats. In the nucleus accumbens core, DA D₁ receptor binding was reduced, D₂ binding was increased and DA release evoked by electrical stimulation of the ventral tegmental area was reduced. Thus, adolescent Ola treatment enduringly alters a key behavioural response to rewarding stimuli and modifies DAergic neurotransmission in the nucleus accumbens. The persistence of these changes suggests that even limited periods of early life Ola treatment may induce enduring changes in other reward-related behaviours and in behavioural and neurobiological responses to therapeutic and illicit psychotropic drugs. These results underscore the importance of improved understanding of the enduring sequelae of paediatric APD treatment as a basis for weighing the benefits and risks of adolescent APD therapy, especially prophylactic treatment in high-risk, asymptomatic patients.

Enhancement of social novelty discrimination by positive allosteric modulators at metabotropic glutamate 5 receptors: adolescent administration prevents adult-onset deficits induced by neonatal treatment with phencyclidine

Metabotropic glutamate-5 receptors (mGluR5), which physically and functionally interact with N-methyl-D-Aspartate (NMDA) receptors, likewise control cognitive processes and have been proposed as targets for novel classes of antipsychotic agent. Since social cognition is impaired in schizophrenia and disrupted by NMDA receptor antagonists like dizocilpine, we evaluated its potential modulation by mGluR5. Acute administration (0.63-40 mg/kg) of the mGluR5 positive allosteric modulators (PAMs), 3-cyano-N-(1,3-diphenyl-1H-pyrazol-5-yl)benzamide (CDPPB) and ADX47273, reversed a delay-induced impairment in social novelty discrimination (SND) in adult rats. The action of CDPPB was blocked by the mGluR5 antagonist, 2-methyl-6-(phenylethynyl)-pyridine (2.5-10 mg/kg), and was also expressed upon microinjection into frontal cortex (0.63-10 μg/side), but not striatum. Supporting an interrelationship between mGluR5 and NMDA receptors, enhancement of SND by CDPPB was blocked by dizocilpine (0.08 mg/kg) while, reciprocally, dizocilpine-induced impairment in SND was attenuated by CDPPB (10 mg/kg). The SND deficit elicited by post-natal administration of phencyclidine (10 mg/kg, days 7-11) was reversed by CDPPB or ADX47273 in adults at week 8. This phencyclidine-induced impairment in cognition emerged in adult rats from week 7 on, and chronic, pre-symptomatic treatment of adolescent rats with CDPPB over weeks 5-6 (10 mg/kg per day) prevented the appearance of SND deficits in adults until at least week 13. In conclusion, as evaluated by a SND procedure, mGluR5 PAMs promote social cognition via actions expressed in interaction with NMDA receptors and exerted in frontal cortex. MGluR5 PAMs not only reverse but also (when given during adolescence) prevent the emergence of cognitive impairment associated with a developmental model of schizophrenia.

Chronic administration of risperidone in a rat model of schizophrenia: a behavioural, morphological and molecular study

In the present work we analyzed the effect of the chronic administration of risperidone (2mg/kg over 65 days) on behavioural, morphological and molecular aspects in an experimental model of schizophrenia obtained by bilateral injection of ibotenic acid into the ventral hippocampus of new-born rats. Our results show that during their adult lives the animals with hippocampal lesions exhibit different alterations, mainly at behavioural level and in the gene expression of dopamine D(2) and 5-HT(2A) receptors. However, at morphological level the study performed on the prefrontal cortex did not reveal any alterations in either the thickness or the number of cells immunoreactive for c-Fos, GFAP, CBP or PV. Overall, risperidone administration elicited a trend towards the recovery of the values previously altered by the hippocampal lesion, approaching the values seen in the animals without lesions. It may be concluded that the administration of risperidone in the schizophrenia model employed helps to improve the altered functions, with no significant negative effects.

Prevention of the phencyclidine-induced impairment in novel object recognition in female rats by co-administration of lurasidone or tandospirone, a 5-HT(1A) partial agonist

Hypoglutamatergic function may contribute to cognitive impairment in schizophrenia (CIS). Subchronic treatment with the N-methyl-D-aspartate receptor antagonist, phencyclidine (PCP), induces enduring deficits in novel object recognition (NOR) in rodents. Acute treatment with atypical antipsychotic drugs (APDs), which are serotonin (5-HT)(2A)/dopamine D(2) antagonists, but not typical APDs, eg, haloperidol, reverses the PCP-induced NOR deficit in rats. We have tested the ability of lurasidone, an atypical APD with potent 5-HT(1A) partial agonist properties, tandospirone, a selective 5-HT(1A) partial agonist, haloperidol, a D(2) antagonist, and pimavanserin, a 5-HT(2A) inverse agonist, to prevent the development of the PCP-induced NOR deficit. Rats were administered lurasidone (0.1 or 1 mg/kg), tandospirone (5 mg/kg), pimavanserin (3 mg/kg), or haloperidol (1 mg/kg) b.i.d. 30 min before PCP (2 mg/kg, b.i.d.) for 7 days (day1-7), followed by a 7-day washout (day 8-14). Subchronic treatment with PCP induced an enduring NOR deficit. Lurasidone (1 mg/kg) but not 0.1 mg/kg, which is effective to acutely reverse the deficit due to subchronic PCP, or tandospirone, but not pimavanserin or haloperidol, significantly prevented the PCP-induced NOR deficit on day 15. The ability of lurasidone co-treatment to prevent the PCP-induced NOR deficit was enduring and still present at day 22. The preventive effect of lurasidone was blocked by WAY100635, a selective 5-HT(1A) antagonists, further evidence for the importance of 5-HT(1A) receptor stimulation in the NOR deficit produced by subchronic PCP. Further study is needed to determine whether these results concerning mechanism and dosage can be the basis for prevention of the development of CIS in at risk populations.

Brain-derived neurotrophic factor and neuropsychiatric disorders

Brain derived neurotrophic factor (BDNF) is the most prevalent growth factor in the central nervous system (CNS). It is essential for the development of the CNS and for neuronal plasticity. Because BDNF plays a crucial role in development and plasticity of the brain, it is widely implicated in psychiatric diseases. This review provides a summary of clinical and preclinical evidence for the involvement of this ubiquitous growth factor in major depressive disorder, schizophrenia, addiction, Rett syndrome, as well as other psychiatric and neurodevelopmental diseases. In addition, the review includes a discussion of the role of BDNF in the mechanism of action of pharmacological therapies currently used to treat these diseases, such antidepressants and antipsychotics. The review also covers a critique of experimental therapies such as BDNF mimetics and discusses the value of BDNF as a target for future drug development.

Fluoxetine and aripiprazole treatment following prenatal immune activation exert longstanding effects on rat locomotor response

AIM

Studies characterizing treatment interventions in a naturalistic setting suggest that antidepressant and antipsychotic medications may be equally effective in improving clinical outcome in individuals at high risk for first-episode psychosis. Of interest, both beneficial as well as potentially adverse effects have been observed following fluoxetine treatment in a mouse prenatal immune activation model of relevance to psychosis prevention. We sought to extend those findings by examining the effects of fluoxetine, as well as the antipsychotic medication aripiprazole, in a rat prenatal immune activation model.

METHODS

Pregnant Sprague-Dawley rats were injected with poly I:C or saline on gestational day 14. Offspring of poly I:C and saline-treated dams received fluoxetine (10.0 mg/kg/d), aripiprazole (0.66 mg/kg/d), or vehicle from postnatal days 35 to 70. Locomotor responses to novelty, saline injection, and amphetamine (1 and 5 mg/kg) were determined at three months, i.e., 21 days following drug discontinuation.

RESULTS

Both fluoxetine and aripiprazole had beneficial effects on behavioral response to amphetamine (1 mg/kg) at 3 months, ameliorating the impact of prenatal immune activation on offspring of poly I:C-treated dams. Significantly, both drugs also exerted effects in offspring of control (saline-treated) dams on locomotor response to injection.

CONCLUSIONS

Fluoxetine and aripiprazole pretreatment of poly I:C offspring from postnatal days 35 to 70 stabilized response to amphetamine exposure persisting through 3 months of age, similar to earlier findings in mice that fluoxetine treatment following prenatal immune activation prevented altered locomotor response to amphetamine. The current data also confirm earlier findings of potential adverse behavioral effects in offspring of control dams following treatment with fluoxetine and antipsychotic medications, highlighting the potential for both therapeutic as well as safety concerns with exposure to preventive pharmacological treatments over the course of adolescent development. Further study is needed to determine clinical and epidemiological consequences of these pre-clinical findings.

Intact neurobehavioral development and dramatic impairments of procedural-like memory following neonatal ventral hippocampal lesion in rats

Neonatal ventral hippocampal lesions (NVHL) in rats are considered a potent developmental model of schizophrenia. After NVHL, rats appear normal during their preadolescent time, whereas in early adulthood, they develop behavioral deficits paralleling symptomatic aspects of schizophrenia, including hyperactivity, hypersensitivity to amphetamine (AMPH), prepulse and latent inhibition deficits, reduced social interactions, and spatial working and reference memory alterations. Surprisingly, the question of the consequences of NVHL on postnatal neurobehavioral development has not been addressed. This is of particular importance, as a defective neurobehavioral development could contribute to impairments seen in adult rats. Therefore, at several time points of the early postsurgical life of NVHL rats, we assessed behaviors accounting for neurobehavioral development, including negative geotaxis and grip strength (PD11), locomotor coordination (PD21), and open-field (PD25). At adulthood, the rats were tested for anxiety levels, locomotor activity, as well as spatial reference memory performance. Using a novel task, we also investigated the consequences of the lesions on procedural-like memory, which had never been tested following NVHL. Our results point to preserved neurobehavioral development. They also confirm the already documented locomotor hyperactivity, spatial reference memory impairment, and hyperresponsiveness to AMPH. Finally, our rseults show for the first time that NVHL disabled the development of behavioral routines, suggesting dramatic procedural memory deficits. The presence of procedural memory deficits in adult rats subjected to NHVL suggests that the lesions lead to a wider range of cognitive deficits than previously shown. Interestingly, procedural or implicit memory impairments have also been reported in schizophrenic patients.

Risperidone administered during asymptomatic period of adolescence prevents the emergence of brain structural pathology and behavioral abnormalities in an animal model of schizophrenia

Schizophrenia is a disorder of a neurodevelopmental origin manifested symptomatically after puberty. Structural neuroimaging studies show that neuroanatomical aberrations precede onset of symptoms, raising a question of whether schizophrenia can be prevented. Early treatment with atypical antipsychotics may reduce the risk of transition to psychosis, but it remains unknown whether neuroanatomical abnormalities can be prevented. We have recently shown, using in vivo structural magnetic resonance imaging, that treatment with the atypical antipsychotic clozapine during an asymptomatic period of adolescence prevents the emergence of schizophrenia-like brain structural abnormalities in adult rats exposed to prenatal immune challenge, in parallel to preventing behavioral abnormalities. Here we assessed the preventive efficacy of the atypical antipsychotic risperidone (RIS). Pregnant rats were injected on gestational day 15 with the viral mimic polyriboinosinic-polyribocytidylic acid (poly I:C) or saline. Their male offspring received daily RIS (0.045 or 1.2 mg/kg) or vehicle injection in peri-adolescence (postnatal days [PND] 34-47). Structural brain changes and behavior were assessed at adulthood (from PND 90). Adult offspring of poly I:C-treated dams exhibited hallmark structural abnormalities associated with schizophrenia, enlarged lateral ventricles and smaller hippocampus. Both of these abnormalities were absent in the offspring of poly I:C dams that received RIS at peri-adolescence. This was paralleled by prevention of schizophrenia-like behavioral abnormalities, attentional deficit, and hypersensitivity to amphetamine in these offspring. We conclude that pharmacological intervention during peri-adolescence can prevent the emergence of behavioral abnormalities and brain structural pathology resulting from in utero insult. Furthermore, highly selective 5HT(2A) receptor antagonists may be promising targets for psychosis prevention.

Animal models of schizophrenia

Developing reliable, predictive animal models for complex psychiatric disorders, such as schizophrenia, is essential to increase our understanding of the neurobiological basis of the disorder and for the development of novel drugs with improved therapeutic efficacy. All available animal models of schizophrenia fit into four different induction categories: developmental, drug-induced, lesion or genetic manipulation, and the best characterized examples of each type are reviewed herein. Most rodent models have behavioural phenotype changes that resemble 'positive-like' symptoms of schizophrenia, probably reflecting altered mesolimbic dopamine function, but fewer models also show altered social interaction, and learning and memory impairment, analogous to negative and cognitive symptoms of schizophrenia respectively. The negative and cognitive impairments in schizophrenia are resistant to treatment with current antipsychotics, even after remission of the psychosis, which limits their therapeutic efficacy. The MATRICS initiative developed a consensus on the core cognitive deficits of schizophrenic patients, and recommended a standardized test battery to evaluate them. More recently, work has begun to identify specific rodent behavioural tasks with translational relevance to specific cognitive domains affected in schizophrenia, and where available this review focuses on reporting the effect of current and potential antipsychotics on these tasks. The review also highlights the need to develop more comprehensive animal models that more adequately replicate deficits in negative and cognitive symptoms. Increasing information on the neurochemical and structural CNS changes accompanying each model will also help assess treatments that prevent the development of schizophrenia rather than treating the symptoms, another pivotal change required to enable new more effective therapeutic strategies to be developed.

Effects of risperidone and paliperidone pre-treatment on locomotor response following prenatal immune activation

AIM

Limited data are available regarding pharmacological characteristics of effective interventions for psychosis prevention. Enrollment challenges in psychosis prevention trials impede screening diverse interventions for efficacy. Relevant animal models could help circumvent this barrier. We previously described prevention with risperidone of abnormal behavior following neonatal hippocampal lesion. We aimed to extend those findings evaluating risperidone and paliperidone following prenatal immune activation, a developmental model of a schizophrenia risk factor. We evaluated a later developmental time point to determine persistent effects of drug treatment.

METHODS

Pregnant Sprague-Dawley rats were injected with poly I:C or saline on gestational day 14. Offspring of poly I:C and saline-treated dams received risperidone (0.45 mg/kg/d), paliperidone (0.05 mg/kg/d), or vehicle from postnatal days 35-70. Locomotor responses to novelty, saline injection, and amphetamine (1 and 5 mg/kg) were determined at three months, i.e., 21 days following antipsychotic discontinuation.

RESULTS

Risperidone and paliperidone had persistent effects on behavioral response to amphetamine (1 mg/kg) at 3 months, ameliorating the impact of prenatal immune activation on offspring of poly I:C-treated dams. Risperidone, but not paliperidone, also exerted persistent effects in offspring of saline-treated dams on locomotor response to saline and amphetamine (5 mg/kg) injection.

CONCLUSIONS

Risperidone and paliperidone pre-treatment of poly I:C offspring during peri-pubertal development stabilized response to amphetamine exposure persisting into early adulthood. Prenatal immune activation provides a model for evaluating effects of an environmental risk factor for schizophrenia, and has potential utility for identifying pharmacological approaches to early intervention.

Cortical disinhibition in the neonatal ventral hippocampal lesion model of schizophrenia: new vistas on possible therapeutic approaches

The neonatal ventral hippocampal lesion (NVHL) model of schizophrenia has been extensively used in many laboratories over the past couple of decades. With more than 120 publications from over 15 research groups, this developmental model yields a number of schizophrenia-relevant behavioral, neurochemical and electrophysiological deficits. An important aspect of this model is the delayed emergence of alterations, typically during adolescence despite the manipulation that causes them having been performed during the first postnatal week. Such delayed timing reflects the periadolescent onset of schizophrenia symptoms and may be related to the protracted maturation of cortical circuits, affected in both the disease and the NVHL model. Here, I will review the work we have done regarding the maturation of prefrontal cortical-accumbens circuits during adolescence, and how this maturation is affected in rats with a NVHL. One of the principal elements affected in NVHL rats is the dopamine modulation of prefrontal cortical interneurons, and this finding is convergent with data from many other developmental, genetic and pharmacological models. An altered maturation of interneuron function would yield a disinhibited cortex, and this opens the way to novel therapeutic approaches for treatment and even prevention of schizophrenia.

Tracing the development of psychosis and its prevention: what can be learned from animal models

Schizophrenia (SCZ) is a neurodevelopmental disorder manifested symptomatically after puberty whose pharmacotherapy remains unsatisfactory. In recent years, longitudinal structural neuroimaging studies have revealed that neuroanatomical aberrations occur in this disorder and in fact precede symptom onset, raising the exciting possibility that SCZ can be prevented. There is some evidence that treatment with atypical antipsychotic drugs (APDs) prior to the development of the full clinical phenotype reduces the risk of transition to psychosis, but results remain controversial. It remains unknown whether progressive structural brain aberrations can be halted. Given the diagnostic, ethical, clinical and methodological problems of pharmacological and imaging studies in patients, getting such information remains a major challenge. Animal neurodevelopmental models of SCZ are invaluable for investigating such questions because they capture the notion that the effects of early brain damage are progressive. In recent years, data derived from such models have converged on key neuropathological and behavioral deficits documented in SCZ attesting to their strong validity, and making them ideal tools for evaluating progression of pathology following in-utero insults as well as its prevention. We review here our recent studies that use longitudinal in vivo structural imaging to achieve this aim in the prenatal immune stimulation model that is based on the association of prenatal infection and increased risk for SCZ. Pregnant rats were injected on gestational day 15 with the viral mimic polyriboinosinic-polyribocytidylic acid (poly I:C) or saline. Male and female offspring were imaged and tested behaviorally on postnatal days (PNDs) 35, 46, 56, 70 and 90. In other experiments, offspring of poly I:C- and saline-treated dams received the atypical antipsychotic drugs (APDs) clozapine or risperidone in two developmental windows: PND 34-47 and PND 48-61, and underwent behavioral testing and imaging at adulthood. Prenatal poly I:C-induced interference with fetal brain development led to aberrant postnatal brain development as manifested in structural abnormalities in the hippocampus, the striatum, the prefrontal cortex and lateral ventricles (LV), as seen in SCZ. The specific trajectories were region-, age- and sex-specific, with females having delayed onset of pathology compared to males. Brain pathology was accompanied by development of behavioral abnormalities phenotypic of SCZ, attentional deficit and hypersensitivity to amphetamine, with same sex difference. Hippocampal volume loss and LV volume expansion as well as behavioral abnormalities were prevented in the offspring of poly I:C mothers who received clozapine or risperidone during the asymptomatic period of adolescence (PND 34-47). Administration at a later window, PNDs 48-61, exerted sex-, region- and drug- specific effects. Our data show that prenatal insult leads to progressive postnatal brain pathology, which gradually gives rise to "symptoms"; that treatment with atypical APDs can prevent both brain and behavioral pathology; and that the earlier the intervention, the more pathological outcomes can be prevented.

Effect of paliperidone and risperidone on extracellular glutamate in the prefrontal cortex of rats exposed to prenatal immune activation or MK-801

The NMDA glutamate hypofunction model of schizophrenia is based in part upon acute effects of NMDA receptor blockade in humans and rodents. Several laboratories have reported glutamate system abnormalities following prenatal exposure to immune challenge, a known environmental risk factor for schizophrenia. Here we report indices of NMDA glutamate receptor hypofunction following prenatal immune activation, as well as the effects of treatment during periadolescence with the atypical antipsychotic medications risperidone and paliperidone. Pregnant Sprague-Dawley rats were injected with polyinosinic:polycytidylic acid (poly I:C) or saline on gestational day 14. Male offspring were treated orally via drinking water with vehicle, risperidone (0.01mg/kg/day), or paliperidone (0.01mg/kg/day) between postnatal days 35 and 56 (periadolescence) and extracellular glutamate levels in the prefrontal cortex were determined by microdialysis at PD 56. Consistent with decreased NMDA receptor function, MK-801-induced increases in extracellular glutamate concentration were markedly blunted following prenatal immune activation. Further suggesting NMDA receptor hypofunction, prefrontal cortex basal extracellular glutamate was significantly elevated (p<0.05) in offspring of poly I:C treated dams. Pretreatment with low dose paliperidone or risperidone (0.01mg/kg/day postnatal days 35-56) normalized prefrontal cortical basal extracellular glutamate (p<0.05 vs. poly I:C vehicle-treatment). Pretreatment with paliperidone and risperidone also prevented the acute MK-801-induced increase in extracellular glutamate. These observations demonstrate decreased NMDA receptor function and elevated extracellular glutamate, two key features of the NMDA glutamate receptor hypofunction model of schizophrenia, during periadolescence following prenatal immune activation. Treatment with the atypical antipsychotic medications paliperidone and risperidone normalized basal extracellular glutamate. Demonstration of glutamatergic abnormalities consistent with the NMDA glutamate receptor hypofunction model of schizophrenia as an early developmental consequence of prenatal immune action provides a model to identify novel early interventions targeting glutamatergic systems which play an important role in both positive and negative symptoms of schizophrenia.

Antipsychotic potential of quinazoline ErbB1 inhibitors in a schizophrenia model established with neonatal hippocampal lesioning

Hyper-signaling of the epidermal growth factor receptor family (ErbB) is implicated in the pathophysiology of schizophrenia. Various quinazoline inhibitors targeting ErbB1 or ErbB2 - 4 have been developed as anti-cancer agents and might be useful for antipsychotic treatment. In the present study, we used an animal model of schizophrenia established by neonatal hippocampal lesioning and evaluated the neurobehavioral consequences of ErbB1-inhibitor treatment. Subchronic administration of the ErbB1 inhibitor ZD1839 to the cerebroventricle of rats receiving neonatal hippocampal lesioning ameliorated deficits in prepulse inhibition as well as those in the latent inhibition of tone-dependent fear learning. There were no apparent adverse effects on basal learning scores or locomotor activity, however. The administration of other ErbB1 inhibitors, PD153035 and OSI-774, similarly attenuated the prepulse inhibition impairment of this animal model. In parallel, there were decreases in ErbB1 phosphorylation in animals treated with ErbB1 inhibitors. These results indicate an antipsychotic potential of quinazoline ErbB1 inhibitors. ErbB receptor tyrosine kinases may be novel therapeutic targets for schizophrenia or its related psychotic symptoms.

Longitudinal MRI monitoring of brain damage in the neonatal ventral hippocampal lesion rat model of schizophrenia

Rat with excitotoxic neonatal ventral hippocampal lesions (NVHL rats) is considered as a heuristic neurodevelopmental model for studying schizophrenia. Extensive study of this model is limited by the lack of clear validity criteria of such lesions and because ascertaining of the lesions is realized postmortem with histological examination after completing experiments. Here, in a first experiment, by assessing the locomotor response to amphetamine in adult NVHL rats, we further specify that the lesions must be bilateral and confined to the ventral hippocampus to obtain the validated behavioral phenotype. We then show a longitudinal magnetic resonance imaging (MRI) protocol suitable for the detection of brain structural changes in NVHL rats. The T(2)-weighted images acquired in adult NVHL rats reveal the same structural changes as those appraised with histological protocol. Moreover, we demonstrate that the lesion status in adulthood can be accurately predicted from the T(2)-weighted images acquired in the juvenile period. As technical advantages, our MRI protocol makes possible to select animals according to lesion criteria as soon as in the juvenile period before long-lasting experiments and gives access in vivo to a quantitative parameter indicative of the lesion extent. Finally, we show that the lesion size increases only slightly between juvenile and adult periods. These latter results are discussed in the context of the specific postpubertal emergence of the behavioral deficits in NVHL rats.

Models of neurodevelopmental abnormalities in schizophrenia

The neurodevelopmental hypothesis of schizophrenia asserts that the underlying pathology of schizophrenia has its roots in brain development and that these brain abnormalities do not manifest themselves until adolescence or early adulthood. Animal models based on developmental manipulations have provided insight into the vulnerability of the developing fetus and the importance of the early environment for normal maturation. These models have provided a wide range of validated approaches to answer questions regarding environmental influences on both neural and behavioral development. In an effort to better understand the developmental hypothesis of schizophrenia, animal models have been developed, which seek to model the etiology and/or the pathophysiology of schizophrenia or specific behaviors associated with the disease. Developmental models specific to schizophrenia have focused on epidemiological risk factors (e.g., prenatal viral insult, birth complications) or more heuristic models aimed at understanding the developmental neuropathology of the disease (e.g., ventral hippocampal lesions). The combined approach of behavioral and neuroanatomical evaluation of these models strengthens their utility in improving our understanding of the pathophysiology of schizophrenia and developing new treatment strategies.

Clozapine administration in adolescence prevents postpubertal emergence of brain structural pathology in an animal model of schizophrenia

BACKGROUND

Schizophrenia is a neuropsychiatric disorder of a neurodevelopmental origin manifested symptomatically after puberty. Structural neuroimaging studies show that neuroanatomical aberrations occur before onset of symptoms, raising a question of whether schizophrenia can be prevented. Treatment with atypical antipsychotic drugs before the development of the full clinical phenotype might reduce the risk of transition to psychosis, but it remains unknown whether neuroanatomical abnormalities can be prevented. We used a neurodevelopmental animal model of schizophrenia to assess the efficacy of the atypical antipsychotic clozapine to prevent neuroanatomical deterioration.

METHODS

Pregnant rats received injection on gestational day 15 with the viral mimic polyriboinosinic-polyribocytidylic acid (PolyI:C) or saline. Structural brain changes in the male offspring were assessed at adolescence and adulthood (35 days and 120 days) with structural neuroimaging. In the second part, male offspring of PolyI:C- and saline-treated dams received daily clozapine (7.5 mg/kg) or saline injection in adolescence (days 34-47) and underwent behavioral testing and imaging at adulthood (from 90 days onward).

RESULTS

In utero exposure to maternal infection led in the offspring to postpubertal emergence of hallmark structural abnormalities associated with schizophrenia, enlarged ventricles, and smaller hippocampus. These abnormalities were not observed in the offspring of mothers who received PolyI:C that were treated with clozapine in adolescence. This was paralleled by prevention of behavioral abnormalities phenotypic of schizophrenia, attentional deficit, and hypersensitivity to amphetamine.

CONCLUSIONS

This is the first demonstration that pharmacological intervention during adolescence can prevent the emergence of brain structural changes resulting from in-utero insult.

Evaluation of animal models of neurobehavioral disorders

Animal models play a central role in all areas of biomedical research. The process of animal model building, development and evaluation has rarely been addressed systematically, despite the long history of using animal models in the investigation of neuropsychiatric disorders and behavioral dysfunctions. An iterative, multi-stage trajectory for developing animal models and assessing their quality is proposed. The process starts with defining the purpose(s) of the model, preferentially based on hypotheses about brain-behavior relationships. Then, the model is developed and tested. The evaluation of the model takes scientific and ethical criteria into consideration.Model development requires a multidisciplinary approach. Preclinical and clinical experts should establish a set of scientific criteria, which a model must meet. The scientific evaluation consists of assessing the replicability/reliability, predictive, construct and external validity/generalizability, and relevance of the model. We emphasize the role of (systematic and extended) replications in the course of the validation process. One may apply a multiple-tiered 'replication battery' to estimate the reliability/replicability, validity, and generalizability of result.Compromised welfare is inherent in many deficiency models in animals. Unfortunately, 'animal welfare' is a vaguely defined concept, making it difficult to establish exact evaluation criteria. Weighing the animal's welfare and considerations as to whether action is indicated to reduce the discomfort must accompany the scientific evaluation at any stage of the model building and evaluation process. Animal model building should be discontinued if the model does not meet the preset scientific criteria, or when animal welfare is severely compromised. The application of the evaluation procedure is exemplified using the rat with neonatal hippocampal lesion as a proposed model of schizophrenia.In a manner congruent to that for improving animal models, guided by the procedure expounded upon in this paper, the developmental and evaluation procedure itself may be improved by careful definition of the purpose(s) of a model and by defining better evaluation criteria, based on the proposed use of the model.

The neonatal ventral hippocampal lesion as a heuristic neurodevelopmental model of schizophrenia

Traditionally, animal models of schizophrenia were predominantly pharmacological constructs focused on phenomena linked to dopamine and glutamate neurotransmitter systems, and were created by direct perturbations of these systems. A number of developmental models were subsequently generated that allowed testing of hypotheses about the origin of the disease, mimicked a wider array of clinical and neurobiological features of schizophrenia, and opened new avenues for developing novel treatment strategies. The most thoroughly characterized (approximately 100 primary research articles) is the neonatal ventral hippocampal lesion (NVHL) model, which is the subject of this review. We highlight its advantages and limitations, and how it may offer clues about the extent to which positive, negative, cognitive, and other aspects of schizophrenia, including addiction vulnerability, represent inter-related pathophysiological mechanisms.

Risperidone alters food intake, core body temperature, and locomotor activity in mice

Risperidone induces significant weight gain in female mice; however, the underlying mechanisms related to this effect are unknown. We investigated the effects of risperidone on locomotor activity, core body temperature, and uncoupling protein (UCP) and hypothalamic orexin mRNA expression. Female C57BL/6J mice were acclimated to individual housing and randomly assigned to either risperidone (4 mg/kg BW day) or placebo (PLA). Activity and body temperature were measured over 48-hour periods twice a week for 3 weeks. Food intake and body weights were measured weekly. UCP1 (BAT), UCP3 (gastrocnemius), and orexin (hypothalamus) mRNA expressions were measured using RT-PCR. Risperidone-treated mice consumed more food (p=0.050) and gained more weight (p=0.0001) than PLA-treated mice after 3 weeks. During the initial 2 days of treatment, there was an acute effect of treatment on activity (p=0.046), but not body temperature (p=0.290). During 3 weeks of treatment, average core body temperatures were higher in risperidone-treated mice compared to controls during the light phase (p=0.0001), and tended to be higher during the dark phase (p=0.057). Risperidone-treated mice exhibited lower activity levels than controls during the dark phase (p=0.006); there were no differences in activity during the light phase (p=0.47). UCP1 (p<0.01) and UCP3 (p<0.05) mRNA expressions were greater in risperidone-treated mice compared to controls, whereas, orexin mRNA expression was lower in risperidone-treated mice (p<0.01). These results suggest that risperidone-induced weight gain in mice is a consequence of increased energy intake and reduced activity, while the elevation in body temperature may be a result of thermogenic effect of food intake and elevated UCP1, UCP3, and a reduced hypothalamic orexin expression.

Psychosis pathways converge via D2high dopamine receptors

The objective of this review is to identify a target or biomarker of altered neurochemical sensitivity that is common to the many animal models of human psychoses associated with street drugs, brain injury, steroid use, birth injury, and gene alterations. Psychosis in humans can be caused by amphetamine, phencyclidine, steroids, ethanol, and brain lesions such as hippocampal, cortical, and entorhinal lesions. Strikingly, all of these drugs and lesions in rats lead to dopamine supersensitivity and increase the high-affinity states of dopamine D2 receptors, or D2High, by 200-400% in striata. Similar supersensitivity and D2High elevations occur in rats born by Caesarian section and in rats treated with corticosterone or antipsychotics such as reserpine, risperidone, haloperidol, olanzapine, quetiapine, and clozapine, with the latter two inducing elevated D2High states less than that caused by haloperidol or olanzapine. Mice born with gene knockouts of some possible schizophrenia susceptibility genes are dopamine supersensitive, and their striata reveal markedly elevated D2High states; suchgenes include dopamine-beta-hydroxylase, dopamine D4 receptors, G protein receptor kinase 6, tyrosine hydroxylase, catechol-O-methyltransferase, the trace amine-1 receptor, regulator of G protein signaling RGS9, and the RIIbeta form of cAMP-dependent protein kinase (PKA). Striata from mice that are not dopamine supersensitive did not reveal elevated D2High states; these include mice with knockouts of adenosine A2A receptors, glycogen synthase kinase GSK3beta, metabotropic glutamate receptor 5, dopamine D1 or D3 receptors, histamine H1, H2, or H3 receptors, and rats treated with ketanserin or aD1 antagonist. The evidence suggests that there are multiple pathways that convergetoelevate the D2High state in brain regions and that this elevation may elicit psychosis. This proposition is supported by the dopamine supersensitivity that is a common feature of schizophrenia and that also occurs in many types of genetically altered, drug-altered, and lesion-altered animals. Dopamine supersensitivity, in turn, correlates with D2High states. The finding that all antipsychotics, traditional and recent ones, act on D2High dopamine receptors further supports the proposition.

Effects of risperidone on locomotor activity and spatial memory in rats with hippocampal damage

Hippocampal damage produces spatial memory impairment and hyperactivity in animals, while reductions in hippocampal size have been associated with memory deficits in humans. There are no known treatments for the behavioral changes specifically related to reduced hippocampal size. The purpose of this study was to determine if risperidone, an atypical antipsychotic drug that has shown cognitive-enhancing properties in animals and humans, could alleviate the behavioral disturbances produced by hippocampal damage in rats. Young adult male Sprague-Dawley rats received either sham stereotaxic surgery or direct stereotaxic infusions of N-methyl-d-aspartate (NMDA) into the dorsal hippocampus to produce hippocampal damage. One week later, animals in each group received daily subcutaneous injections of either saline or risperidone (0.2mg/kg) until the end of the experiment. Three weeks after surgery, locomotor activity was tested in all animals. During the fourth and fifth post-surgical weeks, animals were tested in a discrete-trial, delayed rewarded alternation memory paradigm. Risperidone reversed lesion-induced hyperactivity; however it also decreased activity in the sham control rats. In the delayed alternation task, there were significant drug and lesion effects irrespective of the day of testing, but there was no drugxlesion interaction. Hippocampal lesions impaired performance in the delayed alternation task in saline and risperidone-treated rats. However, risperidone modestly improved performance in lesioned and sham controls in comparison to saline-treated lesioned and sham controls. Risperidone also slowed choice time in the alternation task. These data indicate that risperidone does not specifically correct the neurobiological consequences of hippocampal damage, but that animals with hippocampal damage nonetheless maintain a significant degree of sensitivity to the beneficial effects of risperidone.