Dynorphin-(1-13), dopamine and feeding in rats

Intraventricular administration of the dopamine agonist, bromergocryptine, reliably induces feeding over a narrow dose range with a bell-shaped curve. Bromergocryptine (80 μg) induced feeding is inhibited by the dopamine antagonist, haloperidol (0.5 mg/kg) and the opiate antagonist, naloxone (10 and 1 mg/kg). The leucine-enkephalin containing opioid peptide, dynorphin-(1-13) induces feeding which is inhibited by haloperidol (0.5 and 0.1 mg/kg) and by naloxone (1 mg/kg). Of the common satiety factors tested only bombesin (10 μg/kg subcutaneously) inhibited both dynorphin-(1-13) and bromergocryptine induced feeding. Cholecystokinin-octapeptide (10 and 20 μg/kg, subcutaneously), thyrotropin-relasing hormone (10 and 20 μg), ICV) and calcitonin (1 unit, ICV) all failed to inhibit dynorphin-(1-13)-induced feeding. Calcitonin and CCK-8 but not TRH inhibited bromergocryptine-induced feeding. These studies have demonstrated the close interaction between dopaminergic an dopiate systems in the regulation of food intake. The concept of dopamine being primarily responsible for the initiation of chewing behavior and the opiates regulating food ingestion is compatible with the observations reported here.