Neuronal fields containing luteinizing hormone releasing hormone (LHRH) in mouse brain

Abstract

Immunocytochemical localization of the hypothalamic neurohormone luteinizing hormone releasing hormone (LHRH) was performed in mouse brain using the unlabeled peroxidase anti-peroxidase technique. Antisera derived from serum albumin conjugates to the decapeptide (or its analog) achieved by four conjugation procedures were used to determine the antigenic form of LHRH which reveals the various neuronal compartments. Antisera derived from LHRH conjugated to bovine serum albumin at the 2-histidyl position revealed a population of LHRH-containing cell bodies in the retrochiasmatic area, tuberal area and arcuate nucleus (the LHRH Field I). LHRH-positive fibers and terminals were seen in the organum vasculosum of the lamina terminalis and the median eminence. Fibers from the Field I neurons also coursed rostrally through the medial division of the hypothalamus and circumscribed the anterior commissure or projected dorsally into the thalamus. Antisera generated against conjugates to the N- or C-terminal of LHRH revealed a second population of LHRH perikarya. These were scattered throughout the medial preoptic, preoptic periventricular and medial septal areas (the LHRH Field II). A few neurons were found in the lateral arcuate nucleus. Fibers from septal and preoptic Field II neurons projected to the organum vasculosum. Immunoreactive fibers were found in the median eminence and thalamic regions in patterns similar to those previously described. Median eminence fibers appeared to arise in the regions of Field I neurons which did not stain with the end conjugate antisera. Antisera generated against a LHRH tyrosyl conjugate stained median eminence and organum vasculosum fibers but failed to stain perikarya in either field. The results of this study suggest the presence of two distinct immunoreactive populations of LHRH-containing perikarya, which are not contained within or restricted to any of the recognized hypothalamic nuclei.