Cholinergic nerves of unknown origin in the parotid glands of rats.

The effectiveness of the parasympathetic denervation of the gland caused by avulsion of the auriculo-temporal nerve was investigated. In the first type of experiment, the cholinesterase inhibitor, eserine, was injected through the salivary duct. The substance is thought to preserve acetylcholine leaking from nerve endings, thereby causing secretion of saliva; a secretory response was thus taken as evidence for the presence of cholinergic nerves. In the second type of experiment, the acetylcholinesterase activity of the gland was examined histochemically. From the denervated glands, eserine caused secretion and acetylcholinesterase positive nerves were found in the glands. Both the amount of secretion and the number of nerves were greatly diminished when compared with the intact glands. The results indicate that the denervation procedure was incomplete, leaving some cholinergic nerves unsevered. That cholinergic nerves remain offers an explanation to the residual choline acetyltransferase activity, which has earlier been shown in the gland after avulsion of the auriculo-temporal nerve. To extend the denervation procedure, either avulsion of the facial nerve or avulsion of the superior cervical ganglion was included. Neither procedure abolished the response to eserine or the acetyl-cholinesterase activity, indicating that the routes for the remaining nerves are to be found elsewhere.