Catecholaminergic axons innervate LH-releasing hormone immunoreactive neurons of the human diencephalon

Catecholamines have been shown to modulate gonadal functions via interactio ns with hypothalamic LH-releasing hormone (LHRH)-synthesizing neurons. To r eveal the morphological background of this phenomenon, the distribution of LHRH neurons and tyrosine hydroxylase (TH)-immunoreactive (IR), catecholami nergic structures were mapped in the human diencephalon. First, the locatio n of LHRH and TH-IR neuronal elements was analyzed, and then the relationsh ip between the two different systems was examined. The LHRH-IR cell bodies were mainly present in the medial preoptic and infundibular areas. The TH-I R perikarya were located in the periventricular, paraventricular, and supra optic hypothalamic nuclei and also in the median eminence. The TH-IR fibers were numerous in septal, infundibular, periventricular, and lateral hypoth alamic regions. The brown, diaminobenzidine-labeled LHRH-containing perikar ya were found to receive black, silver-intensified, TH-positive axon termin als in the infundibular and medial preoptic areas. However, in the preoptic and caudal parts of the diencephalon, only a few juxtapositions were noted . The present results indicate that hormone released from diencephalic LHRH -IR neurons in humans may be influenced by the central catecholaminergic sy stem via direct synaptic mechanisms.