Joanna M. Hill National Institute of Mental Health
One of the most significant events in modern neurobiology was the discovery by Ernst and Berta Sharrer ( 1940) that neurons of the hypothalamus synthesize hormones. This discovery was closely followed by the realization that several additional hypothalamic hormones, released into the capillary bed of the hypophyseal stalk, were transported to the anterior pituitary where they regulated anterior pituitary function. The field of neuroendocrinology developed from these discoveries and contributed, among other things, two new and important ideas to biology. First, the detection of hormone-secreting cells in the brain helped to remove the distinction between neurons and endocrine cells and led to a better understanding of the evolutionary development of the endocrine and nervous systems. Second, the feedback regulatory mechanisms in the neuroendocrine system, whereby the secretion of hypothalamic-releasing factors is regulated by the levels of the target organ secretions, replaced the predominant hierarchical views of physiological function with an understanding of the interdependence, and multidirectional communications between systems of the body. The pituitary was no longer the master gland, but a link in the complex mechanism of homeostasis.
Recent progress in neuroscience research has resulted in the formation of some new ideas that may have an equal impact on the future understanding of neurobiology. This chapter reviews some of these new ideas and shows how they lead to the hypothesis that neuropeptides and their receptors not only form the biochemical framework for a communication network in the emotion-mediating regions of the brain but also, perhaps, the framework for a communication system throughout the body.