Neural sites and pathways regulating food intake in birds: A comparative analysis to mammalian systems

The paper reviews hypotheses explaining the regulation of food intake in ma mmals that have addressed specific anatomical structures in the brain. An h ypothesis, poikilostasis, is introduced to describe multiple, homeostatic s tates whereby the regulation of metabolism and feeding occur in birds. Exam ples are given for both wild and domestic avian species, illustrating dynam ic shifts in homeostasis responsible for the changes in body weights that a re seen during the course of an annual cycle or by a particular strain of b ird. The following neural structures are reviewed as each has been shown to affect food intake in birds or in mammals: ventromedial hypothalamic nucle us (n.), lateral hypothalamic area, paraventricular hypothalamic n., n. tra ctus solitarius and area postrema, amygdala, parabrachial n., arcuate n. an d bed n. of the stria terminalis. Two neural pathways are described which h ave been proposed to regulate feeding. The trigeminal sensorimotor pathway is the most complete neural pathway characterized for this behavior and enc ompasses the mechanics of pecking, grasping and mandibulating food particle s from the tip of the bill to the back of the buccal cavity. A second pathw ay, the visceral forebrain system (VFS), affects feeding by regulating meta bolism and the balance of the autonomic nervous system. Wild, migratory bir ds are shown to exhibit marked changes in body weight which are hypothesize d to occur due to shifts in balance between the sympathetic and parasympath etic nervous systems. Domestic avian species, selected for a rapid growth r ate, are shown to display a dominance of the parasympathetic nervous system . The VFS is the neural system proposed to effect poikilostasis by altering the steady state of the autonomic nervous system in aves and perhaps is ap plicable to other classes of vertebrates as well. J. Exp. Zool. 283:348-364 , 1999. (C) 1999 Wiley-Liss, Inc.