Immunohistochemical evidence for the coexistence of cholinergic and catecholaminergic phenotypes in neurones of the vagal motor nucleus in the adult rat.

Catecholaminergic nerve cell bodies have been recently identified in the rat spinal cord. They lie in the rostral cervical segments and at the lumbosacral junction. Among them, many are located in parasympathetic areas. This finding led us to investigate the interactions between these catecholaminergic neurones and the cholinergic ones. To address this question, we performed sequential immunocytochemical detection of choline acetyltransferase (ChAT) and tyrosine hydroxylase (TH) in the same sections. We could then identify the co-expression of both TH and ChAT-like immunoreactivities (LI) in some perikarya of the cervical spinal cord and medulla oblongata. Such cells are located in the caudal extension of the dorsal motor nucleus of the vagus nerve (DMNX) as well as in the caudal part of the medullary DMNX itself. Such a co-expression of TH-LI and ChAT-LI could not be found in the lumbosacral region, another parasympathetic territory where cell bodies displaying TH-LI were intermingled with those containing ChAT-LI. This is one of the first demonstrations of the co-existence of catecholaminergic and cholinergic phenotypes in some neurones of the adult mammalian nervous system. These observations also support the presence of catecholaminergic efferents within the vagus nerve.