Effect of 4-aminopyridine on the rat superior cervical ganglion.

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Abstract
Effect of 4-aminopyridine (4-AP) on the isolated superior cervical ganglion of the rat was investigated by means of the sucrose-gap-method. 4-AP initiated discharges of postganglionic neurons and simultaneously increased the amplitude of the compound action potential evoked by supramaximal preganglionic nerve stimulation at concentrations > 0.1 mM. Ganglionic discharges induced by 4-AP were characterized by low frequency and high amplitude. These 4-AP-induced discharges were unaffected by removal of the preganglionic nerve trunk. These discharges were suppressed by d-tubocurarine, Ca removal from saline or preganglionic denervation, whereas discharges of high frequency and low amplitude were observed after 4-AP in Ca-free solution or in denervated preparations. During perfusion with 4-AP, antidromic action potentials were recorded from the preganglionic nerve. When 4-AP was applied to the preganglionic nerve trunk, postganglionic responses were unaffected. Apparently, discharges of postganglionic neurons were induced by 4-AP, possibly as a result of an initiation of action potentials in preganglionic terminal fibers running in the ganglion.