An electrophysiological in-vivo study on the effects of nerve stimulation, drugs and denervation in the parotid gland of the rat.

Electrical stimulation of the sympathetic and parasympathetic nerves to the parotid gland of the rat gave rise to membrane potential changes. Responses were in several cases elicited by single stimuli which did not cause secretion. They were very similar to the ones seen after the administration of noradrenaline or acetylcholine. The peptides substance P (SP) and vasoactive intestinal polypeptide (VIP), in some cells, evoked membrane potential changes. The response was clearly enhanced during concurrent stimulation of the auriculotemporal nerve at a frequency below the secretory threshold. The membrane potential changes always occurred at stimulation frequencies or agonist doses that were lower or the same as those required for secretion. After atropine the cells became less sensitive to both substance P and VIP. Sympathetic or parasympathetic denervation about 2 weeks in advance, to induce supersensitivity, lowered the thresholds for most agonists just like in vitro. Also as in vitro, a greater number of cells responded to SP and VIP in the denervated than in the innervated gland.