Immunohistochemical demonstration of LHRH-neurons in young rat hypothalamus: light and electron microscopy

Localization and ultrastructural appearance of immunoreactive LHRH neurons were studied in 2-, 8- and 21-day-old rats. The lower half of the diencephalon including the septo-preoptic area was serially cut at 10 microns in the frontal plane, and all sections stained with an anti-LHRH serum were examined light microscopically. Although the antiserum could not demonstrate LHRH-immunoreactive perikarya in adult rats, they were stained in these young rats. The immunoreactive perikarya were scattered in the following regions: nucleus tractus diagonalis, medial septum, medial preoptic area, lateral septum, lateral preoptic area, tuberculum olfactorium, suprachiasmatic area, supraoptic area, pericommisural area, anterior commissure, vascular organ of the lamina terminalis (OVLT), lateral hypothalamic region and lateral tuberal region. The first three regions contained many cells but others showed only sporadical cells. The cells were most frequently observed in 8-day-old rats. Most of the cells appeared to be bipolar showing two immunoreactive processes. Electron microscopy observation was made using the section prepared by a pre-embedding technique. In the immunoreactive perikarya, secretory granules, ribosomal particles, and the particles on the outer surface of endoplasmic reticulum appeared to be immunoreactive, but the Golgi area was immunonegative. The secretory granules appeared along the cytoplasmic membrane but were surprisingly few in number. By contrast, the immunoreactive nerve terminals in the median eminence and in the OVLT contained many granules. These findings suggest that LHRH produced in the perikarya is prompted to be transported and stored in the axonal terminals.