FUNCTIONAL CONNECTIONS OF TONIC AND KINETIC VESTIBULAR NEURONS WITH PRIMARY VESTIBULAR AFFERENTS

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Abstract
Field potentials and single neuronal discharges in the vestibular nuceli were recorded in decerebrate and unanesthetized cats with glass or tungsten microelectrodes. Type-I vestibular neurons were identified as kinetic or tonic in nature with horizontal angular accelerations. All of the type-I vestibular neurons were excited by electric shock to the ipsilateral vestibular nerve, and none of them were inhibited. The kinetic vestibular neurons were mainly monosynaptically excited by primary afferent impulses regardless of the stimulus intensity. The tonic vestibular neurons were excited by minimal intensity of vestibular nerve stimulation with long and dispersed latencies. These delayed spikes of tonic neurons were sensitively blocked by small dose of pentobarbital administration, suggesting multisynaptic activation from primary afferents. The early (N1) and delayed (N2) negative components of the vestibular field potentials were mainly composed of kinetic and tonic neuron spikes, respectively. N2 potentials were characterized by susceptibility to pentobarbital anesthesia and high sensitivity to horizontal rotation as compared to N1.