GASTRIC DISTENSION-INDUCED C-FOS EXPRESSION IN CATECHOLAMINERGIC NEURONS OF RAT DORSAL VAGAL COMPLEX

Functionally specific vagal afferents were stimulated by gastric ballo on distension in unanesthetized rats, followed by double c-fos/dopamin e beta-hydroxylase (DBH) immunocytochemistry, to identify second-order neurons in the dorsal vagal complex. Continuous and repeated phasic d istension with similar volumes produced similar numbers and patterns o f c-fos expression, with most of the activated neurons in the medial a nd commissural nucleus of the solitary tract (NTS) and dorsal motor nu cleus (DMNX). Larger distension activated significantly more neurons i n all responsive areas, but there was no differential effect. In most NTS subnuclei and the DMNX, a small (3-5%) proportion of gastric diste nsion-activated neurons was DBH-immunoreactive (DBH-IR), and this prop ortion did not significantly change with type of distension. With cont inuous and repeated small distensions, 10-12% and, with the large dist ension, 22-30% of all DBH-IR neurons expressed c-fos. The results sugg est a large degree of convergence between rapidly adapting mucosal rec eptors and slowly adapting tension receptors, but not between low- and high-threshold tension receptors, and a relatively minor role of cate cholaminergic second-order neurons in the dissemination of distension signals in the brain.