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.

Cannabidiol Administered During Peri-Adolescence Prevents Behavioral Abnormalities in an Animal Model of Schizophrenia.

Schizophrenia is considered a debilitating neurodevelopmental psychiatric disorder and its pharmacotherapy remains problematic without recent major advances. The development of interventions able to prevent the emergence of schizophrenia would therefore represent an enormous progress. Here, we investigated whether treatment with cannabidiol (CBD - a compound of Cannabis sativa that presents an antipsychotic profile in animals and humans) during peri-adolescence would prevent schizophrenia-like behavioral abnormalities in an animal model of schizophrenia: the spontaneously hypertensive rat (SHR) strain. Wistar rats and SHRs were treated with vehicle or CBD from 30 to 60 post-natal days. In experiment 1, schizophrenia-like behaviors (locomotor activity, social interaction, prepulse inhibition of startle and contextual fear conditioning) were assessed on post-natal day 90. Side effects commonly associated with antipsychotic treatment were also evaluated: body weight gain and catalepsy throughout the treatment, and oral dyskinesia 48 h after treatment interruption and on post-natal day 90. In experiment 2, serum levels of triglycerides and glycemia were assessed on post-natal day 61. In experiment 3, levels of BDNF, monoamines, and their metabolites were evaluated on post-natal days 61 and 90 in the prefrontal cortex and striatum. Treatment with CBD prevented the emergence of SHRs' hyperlocomotor activity (a model for the positive symptoms of schizophrenia) and deficits in prepulse inhibition of startle and contextual fear conditioning (cognitive impairments). CBD did not induce any of the potential motor or metabolic side effects evaluated. Treatment with CBD increased the prefrontal cortex 5-HIAA/serotonin ratio and the levels of 5-HIAA on post-natal days 61 and 90, respectively. Our data provide pre-clinical evidence for a safe and beneficial effect of peripubertal and treatment with CBD on preventing positive and cognitive symptoms of schizophrenia, and suggest the involvement of the serotoninergic system on this effect.

Cannabidiol Prevents Motor and Cognitive Impairments Induced by Reserpine in Rats.

Cannabidiol (CBD) is a non-psychotomimetic compound from Cannabis sativa that presents antipsychotic, anxiolytic, anti-inflammatory, and neuroprotective effects. In Parkinson's disease patients, CBD is able to attenuate the psychotic symptoms induced by L-DOPA and to improve quality of life. Repeated administration of reserpine in rodents induces motor impairments that are accompanied by cognitive deficits, and has been applied to model both tardive dyskinesia and Parkinson's disease. The present study investigated whether CBD administration would attenuate reserpine-induced motor and cognitive impairments in rats. Male Wistar rats received four injections of CBD (0.5 or 5 mg/kg) or vehicle (days 2-5). On days 3 and 5, animals received also one injection of 1 mg/kg reserpine or vehicle. Locomotor activity, vacuous chewing movements, and catalepsy were assessed from day 1 to day 7. On days 8 and 9, we evaluated animals' performance on the plus-maze discriminative avoidance task, for learning/memory assessment. CBD (0.5 and 5 mg/kg) attenuated the increase in catalepsy behavior and in oral movements - but not the decrease in locomotion - induced by reserpine. CBD (0.5 mg/kg) also ameliorated the reserpine-induced memory deficit in the discriminative avoidance task. Our data show that CBD is able to attenuate motor and cognitive impairments induced by reserpine, suggesting the use of this compound in the pharmacotherapy of Parkinson's disease and tardive dyskinesia.

Cannabidiol, among Other Cannabinoid Drugs, Modulates Prepulse Inhibition of Startle in the SHR Animal Model: Implications for Schizophrenia Pharmacotherapy.

Schizophrenia is a severe psychiatric disorder that involves positive, negative and cognitive symptoms. Prepulse inhibition of startle reflex (PPI) is a paradigm that assesses the sensorimotor gating functioning and is impaired in schizophrenia patients as well as in animal models of this disorder. Recent data point to the participation of the endocannabinoid system in the pathophysiology and pharmacotherapy of schizophrenia. Here, we focus on the effects of cannabinoid drugs on the PPI deficit of animal models of schizophrenia, with greater focus on the SHR (Spontaneously Hypertensive Rats) strain, and on the future prospects resulting from these findings.

Effects of cannabinoid drugs on the deficit of prepulse inhibition of startle in an animal model of schizophrenia: the SHR strain.

Clinical and neurobiological findings suggest that the cannabinoids and the endocannabinoid system may be implicated in the pathophysiology and treatment of schizophrenia. We described that the spontaneously hypertensive rats (SHR) strain presents a schizophrenia behavioral phenotype that is specifically attenuated by antipsychotic drugs, and potentiated by proschizophrenia manipulations. Based on these findings, we have suggested this strain as an animal model of schizophrenia. The aim of this study was to evaluate the effects of cannabinoid drugs on the deficit of prepulse inhibition (PPI) of startle, the main paradigm used to study sensorimotor gating impairment related to schizophrenia, presented by the SHR strain. The following drugs were used: (1) WIN55212,2 (cannabinoid agonist), (2) rimonabant (CB1 antagonist), (3) AM404 (anandamide uptake inhibitor), and (4) cannabidiol (CBD; indirect CB1/CB2 receptor antagonist, among other effects). Wistar rats (WRs) and SHRs were treated with vehicle (VEH) or different doses of WIN55212 (0.3, 1, or 3 mg/kg), rimonabant (0.75, 1.5, or 3 mg/kg), AM404 (1, 5, or 10 mg/kg), or CBD (15, 30, or 60 mg/kg). VEH-treated SHRs showed a decreased PPI when compared to WRs. This PPI deficit was reversed by 1 mg/kg WIN and 30 mg/kg CBD. Conversely, 0.75 mg/kg rimonabant decreased PPI in SHR strain, whereas AM404 did not modify it. Our results reinforce the role of the endocannabinoid system in the sensorimotor gating impairment related to schizophrenia, and point to cannabinoid drugs as potential therapeutic strategies.

Effects of cannabinoid and vanilloid drugs on positive and negative-like symptoms on an animal model of schizophrenia: the SHR strain.

Studies have suggested that the endocannabinoid system is implicated in the pathophysiology of schizophrenia. We have recently reported that Spontaneously Hypertensive Rats (SHRs) present a deficit in social interaction that is ameliorated by atypical antipsychotics. In addition, SHRs display hyperlocomotion - reverted by atypical and typical antipsychotics. These results suggest that this strain could be useful to study negative symptoms (modeled by a decrease in social interaction) and positive symptoms (modeled by hyperlocomotion) of schizophrenia and the effects of potential drugs with an antipsychotic profile. The aim of this study was to investigate the effects of WIN55-212,2 (CB1/CB2 agonist), ACEA (CB1 agonist), rimonabant (CB1 inverse agonist), AM404 (anandamide uptake/metabolism inhibitor), capsaicin (agonist TRPV1) and capsazepine (antagonist TRPV1) on the social interaction and locomotion of control animals (Wistar rats) and SHRs. The treatment with rimonabant was not able to alter either the social interaction or the locomotion presented by Wistar rats (WR) and SHR at any dose tested. The treatment with WIN55-212,2 decreased locomotion (1mg/kg) and social interaction (0.1 and 0.3mg/kg) of WR, while the dose of 1mg/kg increased social interaction of SHR. The treatment with ACEA increased (0.3mg/kg) and decreased (1mg/kg) locomotion of both strain. The administration of AM404 increased social interaction and decreased locomotion of SHR (5mg/kg), and decreased social interaction and increased locomotion in WR (1mg/kg). The treatment with capsaicin (2.5mg/kg) increased social interaction of both strain and decreased locomotion of SHR (2.5mg/kg) and WR (0.5mg/kg and 2.5mg/kg). In addition, capsazepine (5mg/kg) decreased locomotion of both strains and increased (5mg/kg) and decreased (10mg/kg) social interaction of WR. Our results indicate that the schizophrenia-like behaviors displayed by SHR are differently altered by cannabinoid and vanilloid drugs when compared to control animals and suggest the endocannabinoid and the vanilloid systems as a potential target for the treatment of schizophrenia.

Contextual exploration previous to an aversive event predicts long-term emotional consequences of severe stress.

Traumatic stress can lead to long-term emotional alterations, which may result in Posttraumatic Stress Disorder (PTSD). Fear reactions triggered by conditioned cues and exacerbated emotional arousal in face of non-conditioned stimuli are among the most prominent features of PTSD. We hypothesized that long-term emotional alterations seen in PTSD may depend on the strength of context-trauma association. Here, we investigated the contribution of previous contextual exploration to the long-term emotional outcomes of an intense foot shock in rats. We exposed male Wistar rats to a highly stressful event (foot shock, 2 mA, 1 sec) allowing them to explore or not the chamber prior to trauma. We, then, evaluated the long-term effects on emotionality. Fear was assessed by the time spent in freezing behavior either upon re-exposure to trauma context or upon exposure to an unknown environment made potentially more aversive by presentation of an acoustic stimulus. Behaviors on the elevated-plus-maze and acoustic startle response were also assessed. The possibility to explore the environment immediately before the aversive event led to differential long-term emotional effects, including a heightened freezing response to re-exposure to context, blunted exploratory behavior, fear sensitization and exacerbation of the acoustic startle response, in contrast to the minor outcomes of the foot shock with no prior context exploration. The data showed the strong contribution of contextual learning to long-term behavioral effects of traumatic stress. We argue that contextual representation contributes to the robust long-term behavioral alterations seen in this model of traumatic stress.

Cannabidiol exhibits anxiolytic but not antipsychotic property evaluated in the social interaction test.

Cannabidiol (CBD), a non-psychotomimetic compound of the Cannabis sativa, has been reported to have central therapeutic actions, such as antipsychotic and anxiolytic effects. We have recently reported that Spontaneously Hypertensive Rats (SHRs) present a deficit in social interaction that is ameliorated by atypical antipsychotics. In addition, SHRs present a hyperlocomotion that is reverted by typical and atypical antipsychotics, suggesting that this strain could be useful to study negative symptoms (modeled by a decrease in social interaction) and positive symptoms (modeled by hyperlocomotion) of schizophrenia as well as the effects of potential antipsychotics drugs. At the same time, an increase in social interaction in control animals similar to that induced by benzodiazepines is used to screen potential anxiolytic drugs. The aim of this study was to investigate the effects of CBD on social interaction presented by control animals (Wistar) and SHRs. The lowest dose of CBD (1mg/kg) increased passive and total social interaction of Wistar rats. However, the hyperlocomotion and the deficit in social interaction displayed by SHRs were not altered by any dose of CBD. Our results do not support an antipsychotic property of cannabidiol on symptoms-like behaviors in SHRs but reinforce the anxiolytic profile of this compound in control rats.

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.

Effects of antipsychotics and amphetamine on social behaviors in spontaneously hypertensive rats.

We have recently reported that spontaneously hypertensive rats (SHRs) exhibit a deficit in contextual fear conditioning that is specifically reversed by antipsychotic and potentiated by psychostimulants and other manipulations thought to produce schizophrenia-like states in rodents. Based on these findings, we suggested that this deficit in fear conditioning could be used as an experimental model of emotional processing impairments observed in schizophrenia. This strain has also been suggested as a model by which to study attention deficit/hyperactivity disorder (ADHD). Considering that schizophrenia and ADHD are both characterized by poor social function, this study aimed to investigate possible behavioral deficits of SHRs in a social context. Furthermore, we sought to examine the effects of typical and atypical antipsychotics (used for the treatment of schizophrenia) and a psychostimulant (used to treat ADHD) on these behaviors. Pairs of unfamiliar rats of the same or different (i.e., Wistar) strains were treated with one of the aforementioned drugs and placed in an open-field for 10min. During this time, social behaviors, locomotion and rearing frequencies were scored. Atypical antipsychotics increased social interaction in Wistar rats (WRs) and improved the deficit in social interaction exhibited by SHRs. In addition, the SHR group displayed hyperlocomotion that was attenuated by all antipsychotics (quetiapine and clozapine also decreased locomotion in WRs) and potentiated by amphetamine (which also increased locomotion in WRs). Our results reveal that the behavioral profile of the SHR group demonstrates that this strain can be a useful animal model to study several aspects of schizophrenia.

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.

The contextual fear conditioning deficit presented by spontaneously hypertensive rats (SHR) is not improved by mood stabilizers.

OBJECTIVES: We have recently reported that spontaneously hypertensive rats (SHR) present a contextual fear conditioning (CFC) deficit. This deficit is improved by antipsychotic drugs, potentiated by proschizophrenia manipulations and not altered by acute administration of carbamazepine, lamotrigine and valproic acid. Nevertheless, the effects of lithium-a classical mood stabilizer-or repeated treatment with these drugs were not evaluated. The main aim of the present study was to extend our previous work by investigating a possible beneficial effect of acute and/or chronic treatments with lithium or lamotrigine on the acquisition deficit of CFC presented by SHR. METHODS: Rats were submitted to CFC task after an acute treatment with lithium and/or a repeated treatment with lithium and lamotrigine. RESULTS: Our data revealed that the CFC deficit presented by SHR is not improved by acute or repeated treatment with lithium. Repeated lamotrigine treatment potentiated the deficit presented by SHR and impaired CFC in control animals (Wistar Rats). CONCLUSIONS: These data reinforce the absence of beneficial effects of mood stabilizers on the emotional context processing impairment modeled by SHR.

Neuroleptic drugs revert the contextual fear conditioning deficit presented by spontaneously hypertensive rats: a potential animal model of emotional context processing in schizophrenia?

Schizophrenia, bipolar disorder, and attention deficit/hyperactivity disorder (ADHD) present abnormalities in emotion processing. A previous study showed that the spontaneously hypertensive rats (SHR), a putative animal model of ADHD, present reduced contextual fear conditioning (CFC). The aim of the present study was to characterize the deficit in CFC presented by SHR. Adult male normotensive Wistar rats and SHR were submitted to the CFC task. Sensitivity of the animals to the shock and the CFC performance after repeated exposure to the task were investigated. Pharmacological characterization consisted in the evaluation of the effects of the following drugs administered previously to the acquisition of the CFC: pentylenetetrazole (anxiogenic) and chlordiazepoxide (anxiolytic); methylphenidate and amphetamine (used for ADHD); lamotrigine, carbamazepine, and valproic acid (mood stabilizers); haloperidol, ziprasidone, risperidone, amisulpride, and clozapine (neuroleptic drugs); metoclopramide and SCH 23390 (dopamine antagonists without antipsychotic properties); and ketamine (a psychotomimmetic). The effects of paradoxical sleep deprivation (that worsens psychotic symptoms) and the performance in a latent inhibition protocol (an animal model of schizophrenia) were also verified. No differences in the sensitivity to the shock were observed. The repeated exposure to the CFC task did not modify the deficit in CFC presented by SHR. Considering pharmacological treatments, only the neuroleptic drugs reversed this deficit. This deficit was potentiated by proschizophrenia manipulations. Finally, a deficit in latent inhibition was also presented by SHR. These findings suggest that the deficit in CFC presented by SHR could be a useful animal model to study abnormalities in emotional context processing related to schizophrenia.