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 other areas of the central nervous system (CNS), suggesting that CB1 receptors may have little functional significance for the vestibular nucleus. However, the dizziness often produced by cannabis suggests that the vestibular system may be implicated. We investigated the effects of the selective CB1 receptor agonist, CP 55940 (the levorotatory enantiomer of desacetyllevonantradol), on medial vestibular nucleus neurons in guinea pig brainstem slices in vitro. Only 3/18 medial vestibular nucleus neurons tested with 1 microM CP 55940 showed changes in firing rate, however these were decreases with an average magnitude of 72.3%; 3/4 neurons tested with 10 microM CP 55940 showed decreases with an average magnitude of 92.7% (P < 0.05 in both cases). In all cases the effects of CP 55940 were long-lasting. These results suggest that despite the low density of CB1 receptors in the vestibular nucleus complex, they may be of functional significance for the behavioural effects of cannabis use.