Influence of a GABA agonist, diazepam, on the vestibuloocular reflexes of the rabbit

We have studied the influence of intravenously administered diazepam on the horizontal (HVOR) and vertical (VVOR) vestibuloocular reflexes of the rabbit, and on the activity of single secondary vestibular neurons. The HVOR was evoked by sinusoidal oscillation of rabbits on a rate table (0.01-0.8 Hz, ± 10 deg) and eye movements were measured with an infrared light projection technique. The gains of the HVOR and VVOR (evoked eye velocity/head velocity) were reduced by diazepam injections of 5 μg/kg. The dose required to produce a 50% reduction in HVOR gain was 500 μg/kg. The time required to reduce the HVOR gain to 50% of its maximal reduction at a dose of 400 μg/kg (0.4 Hz, ± 10 deg) was 60 sec. Intravenous injections of diazepam (20-100 μg/kg) caused a decreased sensitivity of secondary vestibular neurons to sinusoidal angular accelerations. This reduction in sensitivity was observed in secondary neurons which were excited by ipsilateral or contralateral angular acceleration. Thus, diazepam in low doses depresses the vestibuloocular reflex and this reflex depression can be observed at the level of the secondary vestibular neuron. These data suggest that diazepam might be effective as an acute anti-motion sickness agent.