Abstract
Omnipause neurons (OPNs), located near the midline of the pons, discharge tonically at a high rate during fixations and stop firing during saccades in all directions. We have previously reported that the pause of OPN firing is caused by postsynaptic inhibition whose time course closely parallels that of saccadic eye velocity. To clarify the neurotransmitter that mediates the saccade-related inhibition, we studied effects of strychnine, a glycine receptor antagonist, and bicuculline, a GABAA receptor antagonist, on the firing pattern of OPNs in alert cats. Using multibarrel micropipettes, we recorded extracellularly spikes of single OPNs before and after iontophoretic application of the antagonists. Application of strychnine shortened the duration of saccadic pause; the initiation of pause relative to saccade onset was slightly delayed and the resumption of tonic discharge relative to saccade end was markedly advanced. Application of bicuculline had no significant effect on the duration and timing of the pause, but increased tonic firing rate during fixation. These results suggest that inhibitory inputs causing saccadic pause of OPNs are mainly glycinergic. Tonic activity of OPNs for the duration of fixation might be regulated by GABAergic inhibition. [Jpn J Physiol 54 Suppl:S180 (2004)]
