Fourth ventricular capsaicin attenuates suppression of sham feeding induced by intestinal nutrients.

Systemic treatment with capsaicin, a neurotoxin that destroys small unmyelinated primary sensory neurons, causes degeneration of vagal sensory fibers and attenuates suppression of sham feeding by exogenous cholecystokinin (CCK) or intraintestinally infused nutrients. To determine whether capsaicin-sensitive neurons or fibers in the hindbrain mediate suppression of feeding by intestinal nutrients, we examined nutrient-induced suppression of sham feeding in rats pretreated with fourth ventricular capsaicin. Capsaicin treatment abolished the suppression of sham feeding induced by intraperitoneal injection of CCK octapeptide or by intraintestinal maltose. Oleate-induced suppression of sham feeding also was significantly attenuated in capsaicin-treated rats. Capsaicin treatment, however, did not attenuate suppression of sham feeding by intraintestinal L-phenylalanine. These results indicate that capsaicin-sensitive substrates, located near the fourth ventricle, participate in the suppression of sham feeding by CCK and by some intestinal stimuli. Taken together with previously reported data, these results suggest that suppression of sham feeding by some intestinal nutrients is mediated by a neuronal substrate similar or identical to one that mediates suppression of feeding by exogenous CCK.