Capsaicin attenuates suppression of sham feeding induced by intestinal nutrients

Satiety appears to be mediated in part by neurally transmitted signals from the gastrointestinal tract. Capsaicin is a neurotoxin that selectively destroys small unmyelinated primary sensory neurons including some of those innervating the abdominal viscera. Therefore, we examined suppression of sham feeding induced by cholecystokinin octapeptide (CCK-8) or intraintestinal nutrient infusions in capsaicin-treated rats. Suppression of sham feeding induced by CCK-8 was significantly attenuated in rats treated with capsaicin. Suppression of sham feeding induced by intraintestinal infusions of maltose, oleic acid, or L-phenylalanine was also attenuated in capsaicin-treated rats. In contrast, capsaicin treatment did not attenuate the suppression of sham feeding induced by intraintestinal casein hydrolysate (mixed amino acids). Intraintestinal infusions of octanoic acid or D-phenylalanine solutions did not significantly suppress sham feeding in either vehicle- or capsaicin-treated rats. These results indicate that the suppression of feeding by some intestinal stimuli may be mediated by nutrient or peptide-sensitive visceral afferent neurons that are sensitive to damage or destruction by capsaicin.