Cannabinoid-induced motor incoordination through the cerebellar CB1 receptor in mice

Cannabinoids are known to impair motor function in humans and laboratory animals. We have observed dose-dependent motor incoordination in mice evaluated by rotorod following direct intracerebellar (icb) microinjection of synthetic cannabinoid agonists CP55,940 (5 -25 mug) and HU-210 (1.56 -6.25 ll g), through permanently implanted stainless steel guide cannulas. The motor incoordination was marked at 15, 35 and 55 min post-microinjection. The motor incoordination elicited by HU-210 (6.25 mug) and CP55,940 (20 mug) was significantly blocked by the CB1 receptor-selective antagonist SR141716A (25 mug icb), indicating mediation by a cerebellar CB1 receptor. Further direct evidence of CB1 mediation was obtained through a CB1 receptor antisense/mismatch oligodeoxynucleotide approach (3 mug/12 h; total of six doses). Mice treated with intracerebellar antisense had a significantly diminished motor incoordination response to intracerebellar CP55,940 15 mug compared to mice that received intracerebellar mismatch or no prior treatment. Also, the response to intracerebellar CP55,940 in the CB1 mismatch-treated mice did not differ from the mice that received only CP55,940. A separate study using a cerebellar tissue punching technique, following intracerebellar [H-3]-CP55,940 microinjection, confirmed that cannabinoid drug dispersion following microinjections was exclusively confined to the cerebellum. Microinjection of CP55,940 (20 mug) into the hippocampus, an area with a large density of CB1 receptors, did not impair motor coordination Taken together, these results indicate that cannabinoid-induced motor impairment occurs by activation of a CB1 receptor in the cerebellum. The participation of other brain motor areas in cannabinoid-induced motor incoordination will require future study. (C) 2001 Elsevier Science Inc. All rights reserved.