Naloxone suppresses intake of highly preferred saccharin solutions in food deprived and sated rats

In repeated tests naloxone (1 mg/kg, sc) suppressed intake of a narrow range of highly preferred saccharin concentrations (0.1 and 1.0%) in nondeprived male rats but a wider range of concentrations (.001 − 1.0%) following 10 hr. food deprivation. Ins sated rats a low dose of morphine (0.1 mg/kg, sc) had no effect on intake of low concentrations of saccharin but significantly facilitated intake of the highest (10%) and least preferred concentration. These data support the hypothesis that endogenous opioids can modulate the affective quality of gustatory stimuli.