Gastric distension-induced c-fos expression in catecholaminergic neurons of rat dorsal vagal complex.

Functionally specific vagal afferents were stimulated by gastric balloon distension in unanesthetized rats, followed by double c-fos/dopamine beta-hydroxylase (DBH) immunocytochemistry, to identify second-order neurons in the dorsal vagal complex. Continuous and repeated phasic distension with similar volumes produced similar numbers and patterns of c-fos expression, with most of the activated neurons in the medial and commissural nucleus of the solitary tract (NTS) and dorsal motor nucleus (DMNX). Larger distension activated significantly more neurons in all responsive areas but there was no differential effect. In most NTS subnuclei and the DMNX, a small (3-5%) proportion of gastric distension-activated neurons was DBH-immunoreactive (DBH-IR), and this proportion did not significantly change with type of distension. With continuous and repeated small distensions, 10-12% and, with the large distension, 22-30% of all DBH-IR neurons expressed c-fos. The results suggest a large degree of convergence between rapidly adapting mucosal receptors and slowly adapting tension receptors, but not between low- and high-threshold tension receptors, and a relatively minor role of catecholaminergic second-order neurons in the dissemination of distension signals in the brain.