Effects of beta-funaltrexamine on ingestive behaviors in the rat

The effects of beta-funaltrexamine (beta-FNA), an irreversible mu-opioid receptor antagonist, were determined on water and food intake of non-deprived rats. Intracerebroventricular administration of 1.25 or 2.5 micrograms of beta-FNA did not affect drinking or eating. However, 5.0 micrograms first transiently increased food intake and then reduced both water and food intake for at least 72 h. Locomotor activity was unaffected by 5.0 micrograms of beta-FNA; thus, changes in ingestive behavior were not a secondary consequence of drug-induced behavioral stimulation or depression. The early increase in food intake may be due to the short lived and reversible kappa-agonist activity of beta-FNA. On the other hand, selective blockade of mu-opioid receptors appears sufficient to reduce the intake of water and food.