Ingestive responses to mu and delta opioid receptor agonists in the domestic fowl

Abstract

1. Four experiments were conducted using the highly specific mu and delta opioid receptor agonists morphiceptin (B‐casomorphin 1–1, amide) or [Met⁵]‐enkephalin, respectively, to evaluate the effect of mu and delta opioid receptor agonists on ingestive behaviour in the domestic fowl.

2. Intracerebroventricular (ICV) administration of 0.625, 1.25, 2.5 and 5.0 μg of morphiceptin significantly stimulated drinking, while having no effect on feeding. Intramuscular injection of 0.5, 1.5 and 3.0 mg morphiceptin/kg body weight induced a significant increase in feeding, whereas drinking was not altered.

3. ICV administration of 0.625, 1.25, 2.5 and 5.0 μg [Met⁵]‐enkephalin, as well as intramuscular injection of 0.5, 1.5 and 3.0 mg [Met⁵]‐enkephalin significantly stimulated feeding while having no effect on drinking.

4. These results suggest that, in the central nervous system, mu opioid receptor agonists stimulate drinking and delta receptor agonists stimulate feeding. At sites outside the blood‐brain barrier, both mu and delta opioid receptor agonists stimulate feeding.

Notes

Present address: Swine and Poultry Drugs Branch, Center for Veterinary Medicine, US Food and Drug Administration, 5600 Fishers Lane, Rockville, Maryland 20857, USA.