Immunocytochemical localization of luteinizing hormone-releasing hormone and proopiomelanocortin neurons within the preoptic area and hypothalamus of the bovine brain.

The anatomical locations of proopiomelanocortin (POMC) and luteinizing hormone-releasing hormone (LHRH) neurons were examined in brain tissue from peripubertal female calves and from mature, luteal-phase cows. Biotin-avidin-peroxidase procedures were used for single- and double-labeled immunostaining. LHRH perikarya formed a loosely arranged continuum, extending posteriorly from the diagonal band of Broca, passing through the medial and lateral preoptic areas, and ending within the anterior hypothalamic area. LHRH fibers, apparently directed toward the median eminence, passed (1) posteroventrally in the periventricular area and through the arcuate nucleus, and (2) ventromedially lateral to the arcuate nucleus and medial to the supraoptic nucleus. POMC perikarya were located within and about the arcuate nucleus, some penetrating into the median eminence. Fibers from these POMC perikarya passed ventrally to terminate in the median eminence and to regions ventral to the mammillary nuclei. POMC fibers also projected dorsally and laterally from the arcuate nucleus to other hypothalamic regions as well as anteriorly along the third ventricular wall to the preoptic area, bed nucleus of stria terminalis, and stria terminalis. Less than 6% of the POMC or LHRH processes were in close anatomical apposition to LHRH perikarya and dendrites. Extensive intermingling of LHRH and POMC fibers occurred within zona externa of the median eminence.