Immunohistochemical Demonstration of LHRH Neurons and Their Pathways in the Rat Hypothalamus

Abstract

LHRH [luteinizing hormone releasing hormone, lutropin] neurons and fiber tracts were studied immunohistochemically in rats. After the intraventricular infusion of colchicine, a number of immunoreactive LHRH neurons were consistently evident in the preoptico-septal area and in the diagonal band of Broca. The immunoreactive fiber tracts originating in those areas were classified into 2 groups: preoptico-terminal and preopticao-infundibular tracts. The former terminated in the organum vasculosum of the lamina terminalis. The latter was further divided into the mediobasal and laterobasal tracts; both terminated in the median eminence. The mediobasal tract ran posteriorly through the ventral portion of the lateral periventricular area. The laterobasal tract ran posteriorly in the medial forebrain bundle and was accompanied by several immunoreactive neurons. The immunoreactive cell bodies were further scattered in the base of the tuberal hypothalamic area. An anterior bilateral Halasz cut in the retrochiasmatic region was followed by a great reduction of the immunoreactive materials in the median eminence and by the appearance of the immunoreactive perikarya in the preoptico-septal area and in the diagonal band of Broca. A horizontal hypothalamic cut, which disconnected the tubero-infundibular tract between the median eminence and the arcuate nuclei, caused neither reduction of the immunoreactive materials in the median eminence nor appearance of the immunoreactive perikarya in the arcuate nuclei. The bulk of the immunoreactive LHRH is evidently synthesized in the anterior hypothalamic area and transported by the preoptico-terminal and -infundibular tracts, but a minor part is produced in the cell bodies located in the basal tuberal hypothalamus and transported to the median eminence.