Behavioral function of GABA in the median raphe nucleus.

Locomotor hyperactivity of rats was induced by injection of muscimol into the median raphe nucleus. Intra-raphe injection of picrotoxin or bicuculline failed to influence locomotor activity, however, muscimol-induced hyperactivity was inhibited by simultaneous intra-raphe injection of picrotoxin and muscimol. These data indicate an involvement of the GABAergic system in the median raphe nucleus in induction of locomotor effects. Systemic and intra-raphe injection of cyproheptadine depressed muscimol-induced hypermotility, whereas lesion of serotonergic raphe neurons by 5,7-DHT or intra-raphe injected LSD did not influence the muscimol effect, suggesting that GABAergically induced locomotor effects are not entirely mediated by serotonergic mechanisms.