Expression of catecholaminergic characteristics by primary sensory neurons in the normal adult rat in vivo.

Expression of catecholaminergic characteristics by primary sensory neurons was examined in the vagal nodose and glossopharyngeal petrosal ganglia of the normal adult rat in vivo. Catecholaminergic phenotypic expression was documented by immunocytochemical localization of tyrosine hydroxylase (TyrOHase; EC 1.14.16.2), radiochemical assay of specific TyrOHase catalytic activity, and cytochemical localization of formaldehyde-induced catecholamine fluorescence (FIF) within principal ganglion cells. The TyrOHase-containing cells exhibited morphologic features typical of primary sensory neurons, such as an initial axon glomerulus and a single, bifurcating neurite process. These cells were distinguished from TyrOHase- and FIF-positive small intensely fluorescent cells by size, morphology, and staining intensity. TyrOHase-containing neurons appeared to be insensitive to neonatal treatment with 6-hydroxydopamine, thereby distinguishing them from sympathetic neurons. Nodose and petrosal ganglia of adult rats exhibited TyrOHase catalytic activity, linear with respect to tissue concentration over a 10-fold range, indicating that the immunoreactive enzyme was functional. Transection of specific ganglionic nerve roots depleted TyrOHase catalytic activity and neuronal immunoreactivity within the petrosal ganglion, suggesting that target organ innervation regulates enzyme levels within ganglion perikarya. Our study indicates that primary sensory neurons express catecholaminergic transmitter traits in the normal adult rat. Consequently, in the periphery, catecholaminergic characters are not restricted to the sympathoadrenal axis but are expressed by functionally and embryologically diverse populations of autonomic neurons.