[Effects of flunarizine on nystagmus and cochlear blood flow]

The effects of flunarizine (1.25-5 mg/kg, i.v.), a cerebral vasodilator, on nystagmus were compared with those of cinnarizine (2.5-5 mg/kg, i.v.) and diphenidol (2.5-5 mg/kg, i.v.) in rabbits. Flunarizine produced significant decrease in the beat number and duration of caloric-induced nystagmus. On the other hand, cinnarizine and diphenidol decreased the beat number, but hardly shortened the duration. In the same way, these three drugs suppressed the amplitude of the corneocortical potential induced by optokinetic stimulation. However, flunarizine up to 5 mg/kg had no effect on central nystagmus induced by unilateral stimulation to the lateral geniculate body. Flunarizine (0.312-1.25 mg/kg, i.v.), cinnarizine (0.625-2.5 mg/kg, i.v.) and diphenidol (0.625-2.5 mg/kg, i.v.) markedly increased the blood flow in the radiating arteriole of cochlea in the anaesthetized guinea pig. The duration of their increasing activities was in the following order: flunarizine greater than or equal to cinnarizine greater than diphenidol. From these results, it is suggested that the suppression of nystagmus by flunarizine may be at least partly due to the favorable effect on microcirculation in the vestibular organ.