Brain catecholamines and the central control of food intake

Analysis of motivated behaviors indicates the presence of two components, a component that is specific to a particular behavior and a nonspecific component that they all share. Thus, feeding and drinking may be readily differentiated from each other, yet behavioral arousal is a feature of both. Accumulating evidence now suggests that brain catecholamines are involved in the nonspecific aspects of behavior. For example, a variety of sensory stimuli have been shown to increase activity in central catecholaminergic systems measured by electrophysiological, biochemical and electrochemical techniques. Conversely, destruction of these systems leads to a profound decrease in sensory responsiveness. We have been studying the role of the dopamine-containing neurons of the nigrostriatal bundle in motivated behavior. Studies in which dopaminergic activity was monitored in striatum indicate that dopamine release is markedly, though briefly, elevated in response to a variety of intense environmental stimuli, including cold and tail shock. On the other hand, lesions of this pathway impair sensorimotor integration and, thereby, lead to akinesia, sensory neglect and the virtual elimination of all voluntary activities. Moreover, although there is a gradual recovery of function in these brain-damaged animals, they remain less sensitive to stimulation than control animals. For example, they eat but maintain body weight at a level considerably lower than controls, presumably because it takes a greater stimulus of hunger to provoke feeding and less food intake to cause that stimulus to slip below threshold levels of activation. These, and other findings, suggest an important role of brain catecholamines in behavioral arousal, that is, in permitting animals to remain alert and to respond appropriately to relevant sensory stimuli.