Multifiber efferent activity in postganglionic sympathetic and parasympathetic nerves related to the latency of spontaneous and evoked pupillary dilation

Abstract

Spontaneous and peripherally evoked multifiber potentials were recorded from the sympathetic and parasympathetic pupillomotor fibers of the acutely prepared, pharmacologically immobilized cat. The onset latency of change in axonal activity was compared to the onset latency of pupillary dilation of the contralateral iris. Spontaneous pupillary dilations were accompanied by inhibition of parasympathetic and excitation of sympathetic pupillomotor activity. However, parasympathetic inhibition precedes sympathetic excitation. As with spontaneous changes, evoked changes in parasympathetic discharge rate occurred with a shorter onset latency than changes in sympapathetic discharge. In addition, the onset latency of change in sympathetic and parasympathetic nerve discharge was not related to the onset latency of evoked pupillary dilation by a constant factor. The difference in latency of the neural and pupillary response was found to increase systematically as a function of the latency of pupillary dilation.