The action of 5-hydroxytryptamine on single neurones of the rabbit superior cervical ganglion

Intracellular recordings were made from neurones in the rabbit superior cervical ganglion maintained in vitro. Perfusion of the whole ganglion with 5-hydroxytryptamine (5-HT) produced inconsistent and small effects, whereas iontophoretic application of 5-HT induced a depolarization in the majority of neurones. The depolarization was accompanied by a fall in input resistance. The amplitude of the 5-HT potentials was related to the magnitude or duration of the ejection current. The amplitude of the 5-HT potential was augmented by hyperpolarization and decreased by depolarization of the soma membrane of the ganglion cell; it appeared to be linearly related to membrane potential. Iontophoretic responses were reduced in amplitude by superfusion of the ganglion with 5-HT (1 or 50 μM) and by cyproheptadine (50 μM), but unaffected by hexamethonium (500 μM). Tachyphylaxis was apparent when iontophoretic applications were repeated at frequencies of 0.1 Hz or greater.