The mammalian central nervous system has specific neural circuits controlling taste information processing, hunger, appetite, homeostatic state and oral movements, but little is known about the connection between these systems and eating behavior. A candidate neural substrate , however, is the direct projection from the amygdala to the gustatory brainstem. The amygdala has a long acknowledged role in appetite control, novel taste acceptance, and feeding related associative learning. These processes formulate and modify taste preferences which are known to influence food choices and eating behavior. The expression of these behaviors may be via amygdala input acting upon hedonic valence of taste cues and/or oromotor reflex sequences (licking, chewing, and swallowing) in response to taste stimuli. Despite numerous studies documenting the requisite neural circuit, too little is known about the input to the gustatory brainstem to allow definitive conclusions about its functional role. Therefore, the goal of the proposed research is to examine and describe the organization of the direct descending pathway from the amygdala to the rostral nucleus of the solitary tract and parabrachial nucleus using standard neuroanatomical and neurophysiological techniques. The location of the amygdala axonal terminal fields will be related to the known functional organization of the gustatory brainstem nuclei, specifically the overlap and direct synaptic contact with different neural populations characterized as to location of efferent termination and inhibitory function. Neurophysiological studies will determine amygdaloid influences upon parabrachial orosensory neurons. Elucidating the underlying design of this circuit is a necessary step leading to an understanding of the functional link between higher brain processes and orosensory input arising from ingestion. This may be a neural basis for such acute phenomena as illness-related anorexia and conditioned taste aversions, as well as of central neuroregulatory imbalances associated with human appetitive disorders (e.g., obesity, anorexia nervosa and bulimia nervosa).
