Response of guinea pig vestibular nucleus neurons to clicks

Responses of single neurons in the vestibular nuclei to clicks were studied by extracellular recording in anaesthetised guinea pigs. Eighty-four neurons in the ipsilateral vestibular nuclei were activated with an average latency of 1.75 +/- 0.30 ms, which is about 0.9 ms longer than the mean latency of activation of click-sensitive vestibular afferents to intense clicks. The threshold of clicks for evoking the response of these neurons was around 70 dB above the auditory brainstem response threshold. Earlier studies have indicated that click-sensitive vestibular afferents are tilt-sensitive and likely to originate from saccular receptors, and in the present study nine of the click-sensitive vestibular nucleus neurons were tilt-sensitive, suggesting that these central neurons receive monosynaptic input from the corresponding saccular afferents. Recording sites were marked by means of iontophoretic injection of FCF green dye; they were located in the lateral portion of the descending vestibular nucleus and the caudal and ventral regions of the lateral vestibular nucleus.