Neuroanatomical Substrates Involved in the Control of Food Intake

Abstract

Five neural pathways were reviewed regarding their specific role in the control of food intake in birds. The five pathways included the trigeminal sensorimotor system, the visual system/basal ganglia pathway, the gustatory system, the olfactory pathway, and the autonomic nervous system/parasympathetic pathway. The trigeminal system is the pathway best understood among the five systems associated with feeding. It begins with sensory nerves innervating the upper and lower mandibles and buccal cavity and ends with nerves projecting to jaw muscles. The function of the pathway is to control the grasping and mandibulation of pellets or seeds. The visual system includes both the tectofugal and thalamofugal pathways. Both visual pathways interact with the avian paleostriatal complex. The latter is equivalent to the mammalian basal ganglia. The second pathway is important in food recognition as well as in orienting the body with respect to its position in three-dimensional space. The third neural circuit involves the sense of taste. Approximately 300 taste buds have been identified within the buccal cavity of the chicken, suggesting that the gustatory system is better developed than once thought. The fourth pathway involves the olfactory system; as in the visual system, more than one pathway has been identified. The dominant pathway appears to project to the piriform cortex, a structure that may play a role in monitoring essential amino acid contents of the brain. The fifth pathway involves an interaction of the hypothalamus and the dorsal motor nucleus of the vagus. This pathway is important in activating the parasympathetic nervous system and in preparing an organism to feed. All five pathways play different roles in controlling food intake in birds.