Role of the endocannabinoid and endovanilloid systems in an animal model of schizophrenia-related emotional processing/cognitive deficit.

Studies suggest that the endocannabinoid and endovanilloid systems are implicated in the pathophysiology of schizophrenia. The Spontaneously Hypertensive Rats (SHR) strain displays impaired contextual fear conditioning (CFC) attenuated by antipsychotic drugs and worsened by pro-psychotic manipulations. Therefore, SHR strain is used to study emotional processing/associative learning impairments associated with schizophrenia and effects of potential antipsychotic drugs. Here, we evaluated the expression of CB1 and TRPV1 receptors in some brain regions related to the pathophysiology of schizophrenia. We also assessed the effects of drugs that act on the endocannabinoid/endovanilloid systems on the CFC task in SHRs and control animals (Wistar rats - WRs). The following drugs were used: AM404 (anandamide uptake/metabolism inhibitor), WIN55-212,2 (non-selective CB1 agonist), capsaicin (TRPV1 agonist), and capsazepine (TRPV1 antagonist). SHRs displayed increased CB1 expression in prelimbic cortex and cingulate cortex area 1 and in CA3 region of the dorsal hippocampus. Conversely, SHRs exhibited decreases in TRPV1 expression in prelimbic and CA1 region of dorsal hippocampus and increases in the basolateral amygdala. AM404, WIN 55,212-2 and capsaicin attenuated SHRs CFC deficit, although WIN 55,212-2 worsened SHRs CFC deficit in higher doses. WRs and SHRs CFC were modulated by distinct doses, suggesting that these strains display different responsiveness to cannabinoid and vanilloid drugs. Treatment with capsazepine did not modify CFC in either strains. The effects of AM404 on SHRs CFC deficit was not blocked by pretreatment with rimonabant (CB1 antagonist) or capsazepine. These results reinforce the involvement of the endocannabinoid/endovanilloid systems in the SHRs CFC deficit and point to these systems as targets to treat the emotional processing/cognitive symptoms of schizophrenia.

A schizophrenia-like behavioral trait in the SHR model: Applying confirmatory factor analysis as a new statistical tool.

Questionnaires that assess symptoms of schizophrenia patients undergo strict statistical validation, often using confirmatory factor analysis (CFA). CFA allows testing the existence of a trait that both collectively explains the symptoms and gathers the information in a single general index. In rodents, some behaviors are used to model psychiatric symptoms, but no single test or paradigm adequately captures the disorder's phenotype in toto. This work investigated the existence of a behavioral trait in the SHR strain underlying five behavioral tasks used in schizophrenia animal studies and altered in this strain: locomotor activity, rearing behavior, social interaction, prepulse inhibition of startle and contextual fear conditioning. The analysis was conducted on a sample of Wistar (n = 290) and Spontaneously Hypertensive Rats (SHRs, n = 290). CFA showed the existence of a continuous trait in both strains, and higher values among SHRs. This work is the first to demonstrate the existence of a schizophrenia-like trait in an animal model. We suggest that using CFA to evaluate behavioral parameters in animals might facilitate the pre-clinical investigation of psychiatric disorders, diminishing the gap between animal and human studies.

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.

Increased expression of NDEL1 and MBP genes in the peripheral blood of antipsychotic-naïve patients with first-episode psychosis.

Schizophrenia is a multifactorial neurodevelopmental disorder with high heritability. First-episode psychosis (FEP) is a critical period for determining the disease prognosis and is especially helpful for identifying potential biomarkers associated with the onset and progression of the disorder. We investigated the mRNA expression of 12 schizophrenia-related genes in the blood of antipsychotic-naïve FEP patients (N=73) and healthy controls (N=73). To evaluate the influences of antipsychotic treatment and progression of the disorder, we compared the gene expression within patients before and after two months of treatment with risperidone (N=64). We observed a significantly increased myelin basic protein (MBP) and nuclear distribution protein nudE-like 1 (NDEL1) mRNA levels in FEP patients compared with controls. Comparing FEP before and after risperidone treatment, no significant differences were identified; however; a trend of relatively low NDEL1 expression was observed after risperidone treatment. Animals chronically treated with saline or risperidone exhibited no significant change in Ndel1 expression levels in the blood or the prefrontal cortex (PFC), suggesting that the trend of low NDEL1 expression observed in FEP patients after treatment is likely due to factors other than risperidone treatment (i.e., disease progression). In addition to the recognized association with schizophrenia, MBP and NDEL1 gene products also play an essential role in the functions that are deregulated in schizophrenia, such as neurodevelopment. Our data strengthen the importance of these biological processes in psychotic disorders, indicating that these changes can be detected peripherally and potentially represent putative novel blood biomarkers of susceptibility and disorder progression.

Low expression of Gria1 and Grin1 glutamate receptors in the nucleus accumbens of Spontaneously Hypertensive Rats (SHR).

The Spontaneously Hypertensive Rat (SHR) strain is a classical animal model for the study of essential hypertension. Recently, our group suggested that this strain could be a useful animal model for schizophrenia, which is a severe mental illness with involvement of glutamatergic system. The aim of this study is to investigate glutamatergic receptors (Gria1 and Grin1) and glycine transporter (Glyt1) gene expression in the prefrontal cortex (PFC) and nucleus accumbens (NAcc) of SHR animals. The effects in gene expression of a chronic treatment with antipsychotic drugs (risperidone, haloperidol and clozapine) were also analyzed. Animals were treated daily for 30 days, and euthanized for brain tissue collection. The expression pattern was evaluated by Real Time Reverse-Transcriptase (RT) PCR technique. In comparison to control rats, SHR animals present a lower expression of both NMDA (Grin1) and AMPA (Gria1) gene receptors in the NAcc. Antipsychotic treatments were not able to change gene expressions in any of the regions evaluated. These findings provide evidence for the role of glutamatergic changes in schizophrenia-like phenotype of the SHR strain.

Expression profile of neurotransmitter receptor and regulatory genes in the prefrontal cortex of spontaneously hypertensive rats: relevance to neuropsychiatric disorders.

The spontaneously hypertensive rat (SHR) strain was shown to be a useful animal model to study several behavioral, pathophysiological and pharmacological aspects of schizophrenia and attention-deficit/hyperactivity disorder. To further understand the genetic underpinnings of this model, our primary goal in this study was to compare the gene expression profile of neurotransmitter receptors and regulators in the prefrontal cortex (PFC) and nucleus accumbens (NAcc) of SHR and Wistar rats (control group). In addition, we investigated DNA methylation pattern of promoter region of the genes differentially expressed. We performed gene expression analysis using a PCRarray technology, which simultaneously measures the expression of 84 genes related to neurotransmission. Four genes were significantly downregulated in the PFC of SHR compared to Wistar rats (Gad2, Chrnb4, Slc5a7, and Qrfpr) and none in nucleus accumbens. Gad2 and Qrfpr have CpG islands in their promoter region. For both, the promoter region was hypomethylated in SHR group, and probably this mechanism is not related with the downregulation of these genes. In summary, we identified genes that are downregulated in the PFC of SHR, and might be related to the behavioral abnormalities exhibited by this strain.

Effect of antipsychotic drugs on gene expression in the prefrontal cortex and nucleus accumbens in the spontaneously hypertensive rat (SHR).

Antipsychotic drugs (APDs) are the standard treatment for schizophrenia. The therapeutic effect of these drugs is dependent upon the dopaminergic D2 blockade, but they also modulate other neurotransmitter pathways. The exact mechanisms underlying the clinical response to APDs are not fully understood. In this study, we compared three groups of animals for the expression of 84 neurotransmitter genes in the prefrontal cortex (PFC) and nucleus accumbens (NAcc). Each group was treated with a different APD (risperidone, clozapine or haloperidol), and with a non-treated group of spontaneously hypertensive rats (SHRs), which is an animal model for schizophrenia. This study also explored whether or not differential expression was regulated by DNA methylation in the promoter region (PR). In the clozapine group, we found that Chrng was downregulated in the NAcc and six genes were downregulated in the PFC. In the haloperidol group, Brs3 and Glra1 were downregulated, as was Drd2 in the clozapine group and Drd3, Galr3 and Gabrr1 in the clozapine and haloperidol groups. We also encountered four hypermethylated CG sites in the Glra1 PR, as well as three in the risperidone group and another in the haloperidol group, when compared to non-treated rats. Following the APD treatment, the gene expression results revealed the involvement of genes that had not previously been described, in addition to the activity of established genes. The investigation of the involvement of these novel genes can lead to better understanding about the specific mechanisms of action of the individual APDs studied.

Spontaneously Hypertensive Rats (SHR) present deficits in prepulse inhibition of startle specifically reverted by clozapine.

Deficits in an operational measure of sensorimotor gating - the prepulse inhibition of startle (PPI) - are presented in psychiatric disorders such as schizophrenia, bipolar disorder, and attention deficit/hyperactivity disorder (ADHD). Some previous studies showed that the spontaneously hypertensive rats (SHR) present PPI deficit. Although SHR is suggested as an animal model to study ADHD, we have suggested that the behavioral phenotype of this strain mimics some aspects of schizophrenia. The aim of this study was to characterize the PPI response in SHR. Pharmacological characterization consisted in the evaluation of the effects of the following drugs administered to adult Wistar rats (WR) and SHR previously to the PPI test: amphetamine (used for ADHD and also a psychotomimetic drug), haloperidol and clozapine (antipsychotic drugs), metoclopramide (dopamine antagonist without antipsychotic properties) and carbamazepine (mood stabilizer). Our results showed that SHR presented reduced PPI. This deficit was similar to that induced by amphetamine in WR. Only the atypical antipsychotic clozapine improved the PPI deficit observed in SHR. These findings reinforce the SHR strain as an animal model to study several aspects of schizophrenia, including the abnormalities in sensorimotor gating associated with this disease.