Frontal deafferentation of the mediobasal hypothalamus in the neonatal rat and its effects on the preoptico-infundibular LHRH-tract.

By use of the peroxidase-antiperoxidase-complex (PAP) immunohistological method, the preoptico-infundibular LHRH-tract was studied in adult female rats in which frontal hypothalamic deafferentation was performed at the third or tenth postnatal day. In the former group, this LHRH-tract appeared to be similar to that of the intact controls; the animals showed regular vaginal cycles and ova were present in their oviducts. In the latter group, however, marked reduction in the number of the LHRH-nerve fibers was observed behind the sites of the deafferentation in the mediobasal hypothalamus (MBH), whereas LHRH-immunoreactive perikarya and nerve fibers containing the immunoreactive material were seen rostral to the plane of severance. In these animals reduction of LHRH-fibers in the MBH was accompanied by an anovulatory syndrome characterized by constant vaginal cornification and polyfollicular ovaries. Comparing the glial scar formation induced by the cut, significant differences were detected between the two experimental groups. In the animals deafferented on the 3rd day of life, reduction of nerve cells was seen along the cut, but LHRH-fibers crossing the thin glial scar were detectable in large numbers. On the other hand, in the animals deafferented on the 10th postnatal day, extensive glial scar tissue appeared to interrupt the LHRH-fibers rostral to the cut.