Effects of centrally acting muscle relaxants on post-rotatory nystagmus in the rabbit.

1. The effects of some centrally acting muscle relaxants on the post-rotatory nystagmus induced by rotatory stimulation were investigated in the rabbit, to examine the action of the drugs on vestibular function. 2. Tolperisone-HCl (5-10 mg/kg, i.v.) and baclofen (1-3 mg/kg, i.v.) decreased the number of post-rotatory nystagmus beats dose-dependently, whereas mephenesin (40-80 mg/kg, i.v.) and diazepam (0.5-1.0 mg/kg, i.v.) prolonged it dose-dependently. 3. The inhibitory effects of tolperisone-HCl and baclofen may provide some suggestions as to the mechanisms and sites of actions of centrally acting muscle relaxants, while the significance of the prolonging action of mephenesin remains unclear. 4. The prolonging action of diazepam is discussed with reference to GABAergic mechanisms.