Water-avoidance stress-induced c-fos expression in the rat brain and stimulation of fecal output: role of corticotropin-releasing factor.

Immunohistochemical detection of the immediate-early gene c-fos was used to determine the pattern of neuronal activity in the rat brain after exposure to water-avoidance stress known to stimulate fecal output in rats. Avoidance to water for 1 h by standing on a small platform increases pellet output and induces numerous Fos-positive cells in the parvocellular part of the paraventricular nucleus of the hypothalamus (PVN), locus coeruleus (LC) and, to a lesser extent, in the bed nucleus of the stria terminalis, lateral septum, dorsal raphe nucleus and A5 and A1 noradrenergic neurons. The corticotropin-releasing factor (CRF) antagonist, alpha-helical CRF9-41 (50 micrograms i.c.v.) reduced water-avoidance stress-induced c-fos expression mainly in the PVN and the LC (44 and 60%, respectively) and decreased by 60% the stimulated fecal output. These data indicate that water-avoidance stress activates PVN and LC neurons through CRF pathways which contribute to the stimulation of colonic motor function.