Effects of anti-vertigo drugs on medial vestibular nucleus neurons activated by horizontal rotation.

The effects of anti-vertigo drugs on medial vestibular nucleus (MVN) neurons were examined to assess the site and mode of action using cats anesthetized with alpha-chloralose. Single neuron activity in the MVN was extracellularly recorded using a silver wire microelectrode attached along a seven-barreled micropipette, each of which was filled with diphenhydramine, diphenidol, betahistine, glutamate or NaCl. Type I of the MVN neurons were identified according to the responses obtained when the animal placed on a turn-table was rotated sinusoidally. The effects of the drugs were examined on type I neurons which received impulses primarily from the labyrinth and sent them to the oculomotor nuclei. The microiontophoretic application of diphenhydramine, diphenidol and betahistine inhibited rotation-induced firing of type I MVN neurons. Diphenhydramine and diphenidol were more potent than betahistine. These results suggest that these drugs directly act on MVN neurons to reduce the responsiveness to rotatory stimulation.