POTENT EFFECTS OF A SELECTIVE CANNABINOID RECEPTOR AGONIST ON SOME GUINEA-PIG MEDIAL VESTIBULAR NUCLEUS NEURONS

Binding studies have indicated that the density of the cannabinoid CB, receptor is very low in the vestibular nucleus complex compared to ot her areas of the central nervous system (CNS), suggesting that CB, rec eptors may have little functional significance for the vestibular nucl eus. However, the dizziness often produced by cannabis suggests that t he vestibular system may be implicated. We investigated the effects of the selective CB1 receptor agonist, CP 55940 (the levorotatory enanti omer of desacetyllevonantradol), on medial vestibular nucleus neurons in guinea pig brainstem slices in vitro. Only 3/18 medial vestibular n ucleus neurons tested with 1 mu M CP 55940 showed changes in firing ra te, however these were decreases with an average magnitude of 72.3%; 3 /4 neurons tested with 10 mu M CP 55940 showed decreases with an avera ge magnitude of 92.7% (P < 0.05 in both cases). In all cases the effec ts of CP 55940 were long-lasting. These results suggest that despite t he low density of CB1 receptors in the vestibular nucleus complex, the y may be of functional significance for the behavioural effects of can nabis use. (C) 1998 Elsevier Science B.V.