Immunofluorescence study of LRF neurons in man.

Human LRF neurons were characterized by immunofluorescence, using rabbit immunesera against unconjugated synthetic LRF, previously adsorbed on polyvinylpyrrolidone. These neurons, which vary in number from one specimen to another, are mainly concentrated in the mediobasal hypothalamus (infundibular and premammillary nuclei in particular) and in the lamina terminalis and the neighbouring preoptic area. The give rise respectively to a hypothalamo-infundibular LRF tract (ending around the capillaries of the primary portal plexus of the infundibulum) and to a preoptico-terminal tract (ending mainly around the capillaries of the primary and secondary plexuses of the vascular organ of the lamina terminalis and, in addition, between the ependymal cells lining its ventricular surface). It is suggested that these two tracts could be implicated in the tonic and cyclic control of gonadotropic secretion. Some reactive neurons are also present in the septal and pericommissural regions and in the retromammillary area and rostral mesencephalon. These neurons give rise to various extrahypophyseal LRF tracts, probably ending in the telencephalon and the brainstem. It is suggested that LRF, in addition to its major "prehypophysiotropic" action, is able to modulate the activity of certain telencephalic or mesencephalic structures.