The cannabinoid CB1 receptor is involved in the anxiolytic, sedative and amnesic actions of benzodiazepines.

Previous studies in our laboratory showed that cannabinoid CB1 receptor knockout mice (CB1-/-) presented increased anxiety-like behaviours that did not respond to the anxiolytic actions of benzodiazepines. These results suggest that the pharmacological effects of benzodiazepines may involve the participation of cannabinoid CB1 receptors. Therefore, the purpose of this study was to examine the effects of alprazolam and the cannabinoid CB1 receptor antagonist AM251 on behavioural assays (light-dark box test, neurological severity score and step-down inhibitory avoidance test) and on the functional activity of the CB1 receptor (WIN-55,212-stimulated [(35)S] guanosine triphosphate (GTP) gamma binding autoradiography).The administration of alprazolam (40 microg/kg, intraperitoneal (i.p.)) decreased anxiety-like behaviours in the light-dark box test and significantly reduced WIN-55,212-stimulated [(35)S]GTPgamma binding autoradiography in the amygdala and in the CA1 field of the hippocampus, but was without effects on CA2, CA3 and the dentate gyrus (DG) of the hippocampus. The administration of AM251 (3 mg/kg, i.p.) blocked the anxiolytic action of alprazolam (40 microg/kg, i.p.), significantly reduced the sedative (ataxia, neurological severity score in the 0.5 cm bar) and the amnesic actions (short time term memory (1 h after electric shock)) of alprazolam (0.5 mg/kg, i.p.).Taken together, these findings revealed that cannabinoid CB1 receptor plays a pivotal role in the pharmacological actions of benzodiazepines. Furthermore, these results suggest that blockade of cannabinoid CB1 receptors may be useful in the treatment of patients with problems related to the consumption of benzodiazepines. Further clinical trials are needed to test this hypothesis.