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.

Young spontaneously hypertensive rats (SHRs) display prodromal schizophrenia-like behavioral abnormalities.

The Spontaneously Hypertensive Rat (SHR) strain has been suggested as an animal model of schizophrenia, considering that adult SHRs display behavioral abnormalities that mimic the cognitive, psychotic and negative symptoms of the disease and are characteristic of its animal models. SHRs display: (I) deficits in fear conditioning and latent inhibition (modeling cognitive impairments), (II) deficit in prepulse inhibition of startle reflex (reflecting a deficit in sensorimotor gating, and associated with psychotic symptoms), (III) diminished social behavior (modeling negative symptoms) and (IV) hyperlocomotion (modeling the hyperactivity of the dopaminergic mesolimbic system/ psychotic symptoms). These behavioral abnormalities are reversed specifically by the administration of antipsychotic drugs. Here, we performed a behavioral characterization of young (27-50 days old) SHRs in order to investigate potential early behavioral abnormalities resembling the prodromal phase of schizophrenia. When compared to Wistar rats, young SHRs did not display hyperlocomotion or PPI deficit, but exhibited diminished social interaction and impaired fear conditioning and latent inhibition. These findings are in accordance with the clinical course of schizophrenia: manifestation of social and cognitive impairments and absence of full-blown psychotic symptoms in the prodromal phase. The present data reinforce the SHR strain as a model of schizophrenia, expanding its validity to the prodromal phase of the disorder.

Antipsychotic profile of cannabidiol and rimonabant in an animal model of emotional context processing in schizophrenia.

OBJECTIVES: Clinical and neurobiological findings suggest that cannabinoids and their receptors are implicated in schizophrenia. Cannabidiol (CBD), a non-psychotomimetic compound of the Cannabis sativa plant, has been reported to have central therapeutic actions, such as antipsychotic and anxiolytic effects. We have recently reported that spontaneously hypertensive rats (SHR) present a deficit in contextual fear conditioning (CFC) that is specifically ameliorated by antipsychotics and aggravated by proschizophrenia manipulations. These results led us to suggest that the CFC deficit presented by SHR could be used as a model to study emotional processing impairment in schizophrenia. The aim of this study is to evaluate the effects of CBD and rimonabant (CB1 receptor antagonist) on the contextual fear conditioning in SHR and Wistar rats (WR). METHODS: Rats were submitted to CFC task after treatment with different doses of CBD (experiment 1) and rimonabant (experiment 2). RESULTS: In experiment 1, SHR showed a decreased freezing response when compared to WR that was attenuated by 1 mg/kg CBD. Moreover, all CBD-treated WR presented a decreased freezing response when compared to control rats. In experiment 2, SHR showed a decreased freezing response when compared to WR that was attenuated by 3 mg/kg rimonabant. DISCUSSION: Our results suggest a potential therapeutical effect of CBD and rimonabant to treat the emotional processing impairment presented in schizophrenia. In addition, our results reinforce the anxiolytic profile of CBD.