EFFECTS OF BETAHISTINE ON VESTIBULAR RECEPTORS OF THE FROG

Betahistine is widely used in the symptomatic treatment of peripheral and central vestibular disorders. However, its remains unknown whether the drug can act directly on inner ear sensory organs. To this end, t he effects of betahistine (10(-7)-10(-2) M) were examined on isolated preparations of frog semicircular canal mounted in a double-celled bat h which allowed drug administration both in the endolymphatic and in t he perilymphatic fluid. The effects of betahistine were evaluated by r ecording ampullar receptor potentials and nerve firing rate both at re st and during mechanical stimulation of the isolated preparation. The results demonstrated that endolymphatic administration of betahistine had no effect, whereas its perilymphatic administration could reduce g reatly ampullar receptor resting discharge but had little effect on me chanically evoked responses. This observation may explain the anti-ver tigo effects of betahistine, Vertigo is normally due to uncontrolled c hanges in vestibular receptor resting discharge. It is therefore proba ble that any factor able to reduce the resting firing rate of vestibul ar receptors and. in consequence, its variations, may have an anti-ver tigo action.