[Functional anatomy of the hypothalamic-hypophysial system: neuroendocrine control mechanism]

The hypothalamic neuroendocrine mechanisms involved in the regulation of the anterior pituitary functions were reviewed on the basis of the findings obtained mainly in rats. The hypothalamic-hypophysial system has long been considered as a hormonary associated organ system. Recent development of immunohistochemistry and molecular biology, however, has localized the hormone-synthesizing neurons in the hypothalamus, and disclosed the synaptic junctions between them, between those neurons and non-hormonal neurons in the hypothalamus, and further, between neurons in the hypothalamus and other brain parts as well as peripheral nervous systems. Based on these findings, we have designated five functional areas in the hypothalamus: septopreoptic, suprachiasmatic, magno- and parvicellular paraventricular, and arcuate-median eminence areas. The neuronal transmitters in the synaptic junctions were classical transmitters and hormonal or nonhormonal peptides. Some mutual synaptic connections were found between different hormonal peptide-synthesizing neurons within the same area and even between those in the different areas. Although the significance of the neuronal regulation system cooperating with the hormonal events is largely still uncertain, they may serve to integrate the functions of hypothalamic hormone-synthesizing neurons as a whole in adjusting the homeostasis of the internal milieu of the living body. Intimate relations have recently been reported between immune system and endocrine system or hypothalamic neuroendocrine system. In this connection, it is clear that the hypothalamus acts not only as the center for neuroendocrine regulation but also as the center of the neuroendocrine-immune regulation of the living body. To thereby understand the living and reproductive strategies of animals, further accurate knowledge on the neuronal connections within the hypothalamus is needed.