Neuronal Reguration of the Hypothalamic-hypophysial Axis Immunohistochemistry

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We examined the neuronal regulation mechanisms of the hypothalamic-hypophysial system in rats. Our first aim was to find out synaptic associations between hypothalamic hypophysiotrophic hormone-containing neurons and neurons containing neuroactive substances which are known to affect the hypophysiotrophic hormone-containing neurons. Hence we developed a double immunolabeling technique to detect simultaneously different neuroactive substances in pre-and postsynaptic components in combining with intrahypothalamic surgery to transect neuronal pathways or with retrograde tracing of fiber tracts. Additionally we pursued the origins of hypothalamic hypophysiotrophic neurons by using organ culture and transplantation techniques of embryonal hypothalamic tissues. First of all we examined the origin of gonadotrophic hormone roleasing hormono (GaRH)-containing neurons. They derived from the nasal placode : migrating sequentially to the terminal ganglion and further to the internal surface of the … More telencephalon vesicles ; and reaching finally the septo-preoptic area, wherefrom, they extend axonal projections to the developing median eminence to release hormonal GnRH to the portal capiilaries. This suggests that secretory hypophysiotrophic GnRH neurons derive from sensory GnRH neurons. To know what this migration is induced by the nasal placode with the medial basal hypothalamus or cerebral cortex was cultured or transplanted into the third ventricle of adult rats. Secretory neurons with long axonal processes conjugated with blood capillaries to form median eminence like-structures appeared only in the grafts co-transplanted with the medial basal hypothalamus. GnRH neurons in the septo-prepotic area were synaptically regulated by substance P-containing neurons localized in the acurate nucleus. Further we have shown the development of hypothalamic neuropeptide Y-containing neurons and their synaptic associations with vasopressin-containing neurons in the paraventricular nucleus. Furthermore, we have demonstrated the teciprocal regultaory relations between somatostatin-containing neurons and corticotrophin releasing hormone-containing neurons in the parvocellular paraventricular nucleus. Less