Evaluation of CBD effects on the molecular and behavioral changes induced by repeated treatment with MK-801

Abstract

Preclinical and clinical data suggest that cannabidiol (CBD), a major non-psychotomimetic compound from Cannabis sativa, induces antipsychotic-like effects. However, the antipsychotic properties of repeated CBD treatment have been poorly investigated. Behavioral changes induced by repeated treatment with glutamate NMDA receptor antagonists have been proposed as an animal model of schizophrenia-like symptoms. Evidence suggests that NMDA receptor hypofunction could be involved in the negative and cognitive symptoms of schizophrenia. In the present study we evaluated if repeated treatment with CBD would attenuate the behavioral and molecular modifications induced by chronic administration of one of these antagonists, MK-801. Male C57BL/6J mice received daily intraperitoneal injections of MK-801 (0.1, 0.5 or 1 mg/kg) for 14, 21 or 28 days. Twenty-four hours after the last injection animals were submitted to the prepulse inhibition (PPI) test. After that, we investigated if repeated treatment with CBD (15, 30 and 60 mg/kg) would attenuate the PPI impairment induced by chronic treatment with MK-801 (1 mg/kg; 28 days). We also evaluate if the repeated CBD treatment attenuated the MK-801-induced behavioral changes in social interaction and novel object recognition tests. CBD treatment began on the 6th day after the start of MK-801 administration and continued until the end of the treatment. Immediately after the behavioral tests, the mice brains were removed and processed to evaluate the molecular changes. We measured changes on FosB/”FosB and parvalbumin expression, a marker of neuronal activity and a calcium-binding protein expressed in a subclass of GABAergic interneurons, respectively. Changes on mRNA expression of the NMDA receptor GluN1 subunit gene (GRN1) were also evaluated. Additionally, an increasing number of data have linked schizophrenia with neuroinflammatory conditions, and glial cells, such as microglia and astrocytes, have become increasingly attractive as candidates accounting for the pathogenesis of schizophrenia. Besides its antipsychotic properties, CBD also induces anti-inflammatory and neuroprotective effects. Thus, we also evaluated changes on NeuN (a neuronal marker), Iba-1 (a microglia marker) and GFAP (a astrocyte marker) expression in the medial prefrontal cortex (mPFC), dorsal striatum and nucleus accumbens core and shell and dorsal hippocampus by immunohistochemistry. CBD effects were compared to those induced by the atypical antipsychotic clozapine. MK-801 administration at the dose of 1 mg/kg for 28 days impaired PPI responses. Chronic treatment with CBD (30 and 60 mg/kg) attenuated MK801-induced PPI impairment. CBD treatment was also able to attenuate the impairment in social interaction and NOR tests induced by MK-801 treatment. Besides behavioral disruption, MK-801 treatment increased FosB/”FosB expression and decreased parvalbumin expression in the medial prefrontal cortex. A decreased mRNA level of GRN1 in the hippocampus was also observed. Repeated MK-801 treatment also increased the number of GFAP-positive astrocytes in the mPFC and increased the percentage of Iba-1-positive microglia cells with a reactive phenotype in the mPFC and dorsal hippocampus without changing the number of Iba-1-positive cells. In addition, no change on the number of NeuN-positive cells was observed. All the molecular changes were attenuated by CBD. CBD by itself did not induce any effect. Moreover, CBD effects were similar to those induced by repeated clozapine treatment. These results indicate that repeated treatment with CBD, similar to clozapine, reverses the psychotomimetic-like effects and attenuates molecular changes observed after chronic administration of an NMDA receptor antagonist. These data reinforces the proposal that CBD may induce antipsychotic-like effects. Although the possible mechanism of action of these effects is still unknown, it may involve CBD anti-inflammatory and neuroprotective properties. (AU)