Responses of neurons of lizard's, Lacerta viridis, vestibular nuclei to electrical stimulation of the ipsi- and contralateral VIIIth nerves.

Field and intracellular potentials were recorded in the vestibular nuclei of the lizard following stimulation of the ipsi- and contralateral vestibular nerves. The field potentials induced by ipsilateral VIIIth nerve stimulation consisted of an early negative or positive-negative wave (presynaptic component) followed by a slow negativity (transsynaptic component). The spatial distribution of the field potential complex closely paralleled the extension of the vestibular nuclei. Mono- and polysynaptic EPSPs were recorded from vestibular neurons after ipsilateral VIIIth nerve stimulation. In some neurons early depolarizations preceded the EPSPs. These potentials may be elicited by electrical transmission. Often spikelike partial responses were superimposed on the EPSPs. It is assumed that these potentials represent dendritic spikes. Contralateral VIIIth nerve stimulation generated disynaptic and polysynaptic IPSPs in some neurons and EPSPs in others. The possible role of commissural inhibition in phylogeny is discussed. In a group of vestibular neurons stimulation of the ipsilateral VIIIth nerve evoked full action potentials with latencies ranging from 0.25-1.1msec. These potentials are caused by antidromic activation of neurons which send their axons to the labyrinth.