Effects of ethyl alcohol and heavy-water administration on vestibulo-ocular reflex in rabbits.

The effects of ethyl alcohol and heavy water on the long-time constant (T1) of the vestibulo-ocular reflex, an index of the dynamics of the cupula-endolymph system of the semicircular canal, were investigated in rabbits. Ethyl alcohol with a specific gravity of 0.793 caused two types of direction-changing positional nystagmus. In the early period after its administration, geotropic type positional nystagmus was induced. In this period, ethyl alcohol reduced T1. In the later period after its administration, apogeotropic type positional nystagmus was induced. In this period, T1 was again prolonged. Heavy water with a specific gravity of 1.10 caused apogeotropic type positional nystagmus and prolonged T1. These findings demonstrated that ethyl alcohol and heavy water directly affect the cupula-endolymph system, suggesting that the semicircular canal was responsible for the positional nystagmus.