The Role of Central Endogenous Opioid Peptides in the Feeding Behavior of Rats : Its Relevance to GABAergic and Adrenergic Systems

Abstract

Central endogenous opioid peptides are generally known to play an important role in the feeding behavior of rats. Several experimental hyperphagia rats were pretreated with naloxone, an opioid peptide receptor antagonist, to observe the changes in the feeding behavior. The intracerebroventricular (i.c. v.) administration of naloxone suppressed the hyperphagia caused by fasting, the subcutaneous injection of diazepam (a benzodiazepine antianxietic drug), and the i.c.v. administration of muscimol (a GABA agonist), clonodine (an co-adrenaline agonist) and 2-deoxy-D-glucose (a glucose metabolite). The i.c.v. administration of thiorphan, an enkephalinase inhibitor, on the other hand, increased the food intake of satiated rats. These results suggested that the central endogenous opioid peptides would control the activity of the central a2-adrenergic and GABAergic systems on the feeding behavior of rats. The central opioid peptidergic system would play a significant role in the central regulation of the physiological feeding behavior of rats.