Descending luteinizing hormone-releasing hormone (LH-RH) nerve fibers to the midbrain of the rat.

Using the peroxidase-antiperoxidase complex (PAP) immunohistological method, a luteinizing hormone-releasing hormone (LH-RH)-containing nerve fiber tract was detected in the mesencephalon of intact rats, and in rats bearing a symmetrical cut in the coronal plane at the level of the superior collicle reaching down to the ventral tegmental decussation. This LH-RH fiber tract was found in subependymal position in the mesencephalic central gray. The LH-RH fibers reached the ponto-mesencephalic junction in the intact animals, whereas in the experimental group they were absent behind the cut. These findings indicated that the direction of the LH-RH axons in the mesencephalic central gray is descending.