A study of the structure and functions of the submandibular ganglion.

The submandibular ganglion (SMG) of both the rat and monkey is composed of a collection of small ganglia distributed mainly at the hilum of the submandibular gland. Ultrastructurally, its constituent neurons have a prominent nucleus and numerous randomly distributed cytoplasmic organelles. In the rat SMG a variable number of its neurons are immunoreactivities for [Met5]enkephalin-Arg6-Gly7-Leu8, neuropeptide Y (NPY), substance P (SP), tyrosine hydroxylase (TH) and vasoactive intestinal polypeptide (VIP). In the monkey, however, the SMG neurons only react for NPY and SP. Following sectioning of the lingual nerve, SMG neurons of both the rat and monkey showed structural alterations; a marked change was also observed in the immunoreactivities of the rat neurons. There were signs of recovery in the structural features and immunoreactivities in the SMG neurons in animals with longer survival periods of up to 2 months. This suggests that the changes in the neurons after denervation are acute but reversible in nature. After fluorogold injections into the submandibular and sublingual glands of the rat, a variable number of neurons in the superior salivatory nucleus (SSN), superior cervical ganglion (SCG) and trigeminal ganglion (TG) were labelled. A hypothetical model depicting the possible interactions between the parasympathetic SMG and the preganglionic nucleus, that is, the SSN, as well as the sympathetic SCG and the sensory TG is presented. It is proposed that the SMG functions as a relay as well as a modulatory centre for salivatory activity.