Understanding the neural control of ingestive behaviors: Helping to separate cause from effect with dehydration-associated anorexia

Eating and drinking are motivated behaviors that are made up of coordinated sets of neuroendocrine, autonomic, and behavioral motor events. Although t he spinal cord, hindbrain, and hypothalamus contain the motor neurons and c ircuitry sufficient to maintain the reflex parts of these motor events, inp uts from the telencephalon are required to furnish the behavioral component s with a motivated (goal-directed) character. Each of these motor events de rives from the complex interaction of a variety of sensory inputs with grou ps of neural networks whose components are distributed throughout the brain and collectively support motor expression and coordination. At a first app roximation based on a variety of data, these networks can be divided into t hree groups: networks that stimulate, those that inhibit, and those that di sinhibit motor functions. A fourth contributor is the circadian timing sign al that originates in the hypothalamic suprachiasmatic nucleus and provides the temporal anchor for the expression of all behaviors. This article disc usses the nature of these networks using neuroanatomical (tract-tracing and neuropeptide in situ hybridization), endocrine, and behavioral evidence fr om a variety of experimental models. A persistent problem when studying the control of food intake from a neural systems perspective has been the diff iculty in separating those neuronal changes that result in hunger from thos e that are as a consequence of eating. To address this problem, dehydration -associated anorexia is presented as a particularly useful experimental mod el because it can be used to distinguish between neural mechanisms underlyi ng anorexia and those changes that occur as a consequence of anorexia. The article concludes by highlighting the potential role of neuropeptidergic ac tion in the operation of these networks, using forebrain neuropeptidergic i nnervation of the parabrachial nucleus as an example. (C) 2000 Academic Pre ss.