Role of hypothalamic circuitries in neuroendocrine regulations: hypothalamus - endocrine pancreas interactions, a new concept.

Though there is no lack in proofs of hypothalamic involvement in regulating endocrine pancreas and related aspects of metabolism, the mechanisms thereof are still pending elucidation. There is no adequate tropic hormone in the anterior pituitary hence the conventional hypothalamic-hypophyseal route may only function as circuitous. This lends special appeal to a probable hypothalamic participation over purely neural route, one implicated in insulin secretion, for example via the vagus. This has long been considered possible but has not been explored. Summed up are results of many years of experimental research by the author and his group in hypothalamic-vagal neural connections. The following techniques were employed: karyometric and relevant histochemical studies of rat medullary vagal nuclei and hypothalamic nuclei under insulin deficiency; karyometric studies of transneuronal changes in dorsal vagal nuclei, as well as silver impregnation studies of preterminal axons and their terminal branches (Fink-Heimer technique) for degeneration together with ultrastructural studies of presynaptic profile degeneration in dorsal vagal nuclei of rats bearing electrolytic lesions placed in the hypothalamic areas, in which descending axons are presumed to originate. The results obtained indicate there exists a direct hypothalamic-vagal descending pathway, which originates in paraventricular nuclei and synapses on neurons of the dorsal vagal nuclei after partial crossing over in the lower brain stem. Possible mechanisms at hypothalamic and medullary levels in neuroendocrine regulations of pancreatic islets are discussed.