Attenuation of sham feeding by naloxone is stereospecific: evidence for opioid mediation of orosensory reward.

The time course of the suppressive action of naloxone on sham feeding was examined in gastric fistulated rats. One hour sham intake of 30% sucrose solution was halved by 1.25 mg/kg IP (-)-naloxone. A maximal 75% reduction was obtained with 2.5 mg/kg. Naloxone's effect appeared to mimic the attenuation of intake rate produced by sucrose dilution. The stereoisomer (+)-naloxone (1.25, 2.5 and 10 mg/kg IP) was ineffective. These data confirm the involvement of opioid receptors in naloxone anorexia and are consistent with opioid involvement in the rewarding aspects of ingestion.