Effect of 4-aminopyridine on the rat superior cervical ganglion

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 higher than 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, however, postganglionic responses were unaffected. It is suggested that discharges of postganglionic neurons were induced by 4-AP, possibly as a result of an initiation of action potentials in preganglionic terminal fibres running in the ganglion.