Acceleration of tail pinch-induced feeding in rats by analgesic effect of neurotropin.

Mechanisms of tail pinch-induced feeding and effects of neurotropin (NSP), an extract from the inflamed skin of rabbit inoculated with vaccinia virus, on behavioral responses were investigated in rats. Treatment of a 5-min tail pinch (tail pinch I) induced feeding response. An intensified 15-min tail pinch (tail pinch II) provoked emotional reactions besides feeding behavior. The rate of food intake (food intake/tail pinch duration) during tail pinch II was less than that at tail pinch I. Intraperitoneal administration of NSP (100 mg/kg/day) by itself produced no remarkable change in feeding or emotional behavior. However, NSP-treated rats increased eating size and prolonged eating duration during tail pinch I. Pretreatment of NSP increased feeding behavior more potently at tail pinch II than at tail pinch I and decreased the incidence of emotional reactions at tail pinch II. The results suggest that NSP, by its analgesic action, may modulate behavioral responses during tail pinch treatment through selective blockade of the nociceptive and feeding-inhibitory information, but not through the nonnociceptive and feeding-excitatory signals.