COMPARISON OF THE STIMULATING EFFECTS OF NICOTINE, PILOCARPINE AND HISTAMINE ON THE SUPERIOR CERVICAL GANGLION OF THE CAT

¹ Department of Pharmacology, State University of New York, School of Medicine, Buffalo, New York

The objectives of this study were to characterize and compare the effects of nicotine, pilocarpine and histamine on the superior cervical ganglion of the pithed cat by recording isometric contractions of the nictitating membrane evoked by injection of the agonists into the common carotid artery. The relationship between dose of histamine and pilocarpine and the duration of tachyphylaxis was determined. In subsequent experiments, sufficient time between doses was allowed to permit recovery from tachyphylaxis. Repetitive electrical stimulation of the preganglionic nerve markedly enhanced the ganglion-stimulating effects of pilocarpine and histamine. A method of systematic repetitive stimulation of the preganglionic nerve was developed, which maintained the ganglion in a relatively stable, sensitized state for prolonged periods of time. The slopes of the doseresponse curves and the maximum force obtained for nicotine, histamine and pilocarpine with sensitized ganglia were different. Hexamethonium, atropine and pyrilamine were specific surmountable antagonists of nicotine, pilocarpine and histamine, respectively. Because of the highly specific blocking effects of the antagonists, it is concluded that nicotine, pilocarpine and histamine act at different receptor sites on or in ganglion cells; hence, the sensitization following repetitive preganglionic nerve stimulation is probably due to alteration of the ganglion cells.