Immunohistochemical study of the onset of hormone synthesis in LH-RH and somatostatin neurons in rat brain.

The onset of hormone synthesis in LH-RH and somatostatin neurons of the brain was studied in rats using the unlabelled antibody-PAP immunohistochemical method. LH-RH appeared in detectable amounts first in neuronal perikarya in the preoptic region of fetuses sacrificed on the 17th day of gestation. Minute amounts of LH-RH could already be detected in some nerve fibers of the preoptic region of fetuses on the 18th gestational day. On the 19th day the vascular organ of the lamina terminalis (OVLT) and on the 20th day the median eminence (ME) already contained loose networks of nerve fibers and axon terminals accumulating LH-RH. Somatostatin perikarya and axon terminals with detectable amounts of the hormone appeared simultaneously on the first postnatal day in the anterior periventricular region and the median eminence, respectively. Somatostatin containing nerve fibers became detectable in OVLT first on the 2nd day of life.