Naloxone-induced suppression of food intake is potentiated by neonatal administration of monosodium glutamate to mice.

The anorectic potency of naloxone and fenfluramine was evaluated in mice treated neonatally with 4 mg/g of MSG. Naloxone produced a specific and pronounced suppression of food intake in MSG-treated mice, whereas fenfluramine was equipotent in suppressing food intake for both MSG-treated and control mice. Naloxone at doses of 5, 10 and 20 mg/kg was significantly more potent in suppressing food intake in MSG-treated mice when compared to controls. Water intake, however was suppressed to a greater extent in control mice than MSG-treated mice following administration of either naloxone or fenfluramine. These results implicate endogenous opiate systems in the obesity and alterations in food intake regulation exhibited by MSG-treated mice.