Topographic relations between tyrosine hydroxylase- and luteinizing hormone-releasing hormone-immunoreactive fibers in the median eminence of adult rats.

Employing electron microscopic double immunolabeling, we determined a close apposition of tyrosine hydroxylase (TH) and luteinizing hormone-releasing hormone (LHRH) nerve fibers in the rat median eminence (ME). These axo-axonic contacts occurred frequently in the internal and palisade zones, i.e. at the level of the fiber preterminals. In the superficial area of the ME, major TH fibers abutted on the basal lamina and some were projected into the pericapillary space of the portal vessels. Conversely, LHRH fibers were arrested by the endfeet of tanycytes in reaching the basal lamina.