Localization of serotonin fibers in the rat adenohypophysis.

Immunocytochemical staining for serotonin, 5-hydroxytryptamine, in frozen sections of the pituitary resulted in the localization of fine, varicose fibers in specific regions of the adenohypophysis. Stained fibers with beaded varicosities were observed entering the rostral zone of the adenohypophysis with blood vessels, coursing over the surface of the anterior lobe, and splitting into fine, varicose fibers in deeper portions of the lobe. In both horizontal and sagittal sections, fibers were observed extending from the periphery of the gland to penetrate between the first 2-3 cell layers. The intermediate lobe was even more extensively innertvated by fibers staining for serotonin. These studies suggest that fiber systems containing serotonin innervated the adenohypophysis and can be detected with the most sensitive immunocytochemical methods.