Effects of halothane on the vestibulo-ocular reflex.

The differential effect of halothane on the characteristics of fast and slow components of vestibular nystagmus was investigated in rabbits. Eye movements were monitored using the "magnetic search coil" method and evaluated with the aid of a laboratory minicomputer. Low concentrations of halothane act preferentially on the fast component. There is a shift of the position threshold of fast component generation toward the periphery of the orbit and a diminution of the eye velocity during this nystagmus phase. Higher steady state concentrations of halothane reduced the velocity of the slow components whereby there is an increase in the amplitude of stimulation necessary to produce vestibulo-ocular responses of a magnitude to exceed the threshold of fast components. The results support the hypothesis that there are independent neural pathways for the production of fast and slow components of nystagmus whose neurons have different sensitivities to anesthetic agents.