Food intake regulation in birds

Food intake regulation in birds represents a complex homeostatic mechanism involving multiple levels of control. This review discusses the role of var ious neurotransmitters and nutrients in regulating food intake. These compo unds have effects on food intake when injected both inside and outside the blood-brain barrier. Food intake is decreased when various compounds includ ing epinephrine, amino acids, glucose, and fatty acids are infused directly into the hepatic portal blood system. Furthermore, genetic selection for i ncreased body weight as has occurred in broiler type chickens has altered t he food intake response to such infusions. Food intake has not been increas ed by injections into the liver. A considerable number of neurotransmitters have also been shown to either increase or decrease food intake when injec ted directly into the central nervous system. Genetic selection, physiologi cal state of the bird, and the site of injection influence the response to these compounds. When injected into the brain, neuropeptide Y, avian pancre atic polypeptide, and opioids are potent stimulators of food intake whereas other peptides investigated to date decrease food intake. While many aspec ts of food intake regulation in birds appear similar to that in mammals, th ere are some responses that are unique to birds. J. Exp. Zool. 283:333-338, 1999. (C) 1999 Wiley-Liss, Inc.