Figure 8.

Determination of the cellular substrate underlying GVS-induced spike discharge in vestibular nerve afferents. A, Single-unit recordings of HC afferents during horizontal turntable rotation (red dashed arrow) and GVS of the HC cupula (green stimulus electrode); note that the GVS electric field (dashed field lines) expands between the HC electrode and a distant one in the Ringer's solution. B–D, Single HC afferent fiber discharge during horizontal rotation (magenta traces in B, D) and GVS of the HC cupula (green traces in B, D) before (B) and during (D) bath application of CNQX (15 μm) and 7-Cl-KYNA (50 μm) that blocked the synaptic transmission between hair cells and vestibular afferent fibers pharmacologically (C). E, F, Averaged single-unit afferent discharge over one cycle of GVS (from 16 cycles, ±SEM, shaded areas; n = 13) at two stimulus intensities (±30 μA, ±150 μA; E) and dependency of GVS-induced peak afferent firing rate on stimulus intensity (F) before (control, black symbols) and during pharmacological block of the glutamatergic hair cell–afferent synapse (red symbols); green dashed line in F depicts the arithmetic difference between the two conditions, indicating the magnitude of hair cell contribution to the GVS-induced afferent discharge. Scale bar in B applies to all traces in B and D.