The Hypothalamus: New Ideas on an Old Structure
The present seminar has brought up many of the fascinating ideas presently accepted concerning the functions of the hypothalamus. Summarizing them is an extremely difficult task. At the same time it constitutes a challenge, since the subject dealt with is of great practical importance, not only due to its interdisciplinary range but also to its integrative potential much in the same way as the hypothalamus itself appears to be one of the main integrative centres of the brain (if not the major one). It is certain that when Sherrington wrote his Integrative Action of the Nervous System 1 he was far from thinking in the terms of today, but already the classical work of Papez2 represented a preview of modern concepts. The conceptual shifting from a topographic mapping of hypothalamic “centres” towards a more dynamic approach thanks to biochemical studies has, no doubt, led to a new era in neuroendocrinology. It is now known that the afferents to the hypothalamus are not necessarily neuronal but may also be humoural (both CSF- and blood-borne). Further, it has become apparent that hypothalamic cell groups concentrate medially, perhaps seeking for proximity to the CSF spaces, perhaps because this is the deepest and most protected part of the brain, while the lateral hypothalamus is rich in fibers and appears to constitute part of a wide communication system. Efferents from this system reach not only centres in the medulla oblongata, such as the locus coeruleus, but may extend even to the lumbosacral levels in the intermediate grey column. These efferents emanate from the dorsal and from the lateral parvocellular districts of the para-ventricular nuclei, and many of them use oxytocin as transmitter substance.