Ventromedial and lateral hypothalamic injections of naloxone or naltrexone suppress the acute food intake of food-deprived rats.

Experiments were conducted to determine the anorexigenic effects of ventromedial (VMH) and lateral hypothalamic (LH) injections of the mu-opiate receptor antagonists, naloxone and naltrexone, on food-deprived (20 h) rats. Lever pressing to obtain food pellets was measured in groups of hungry, male Sprague-Dawley rats following VMH, LH or subcutaneous (SC) injections of saline, naloxone or naltrexone. VMH injections of either narcotic antagonist (5 and 10 micrograms/microliter) and LH injections of naloxone (5 and 10 micrograms/microliter) decreased the total 90-min food intake, compared to saline controls, due to suppressed feeding especially during the initial 30-min interval. Rats given SC injections of naloxone (10 mg/kg) also decreased their food intake compared to amounts eaten after SC saline was given. Decrements in food consumption relative to saline controls were similar following VMH or LH administration of naloxone. Moreover, the anorexia observed following VMH naloxone administration was similar to that found after VMH injections of equal doses of naltrexone.