Serotonin immunoreactive nerve fibers and terminals in the rat pituitary--light- and electron-microscopic studies.

Serotonin-immunoreactive nerve fibers were demonstrated to form a plexus in the intermediate lobe of rat pituitary. Such fibers were sporadic in the posterior lobe where they occurred exclusively in the zone adjacent to the intermediate lobe, and in the anterior lobe. With the aid of electron-microscopic immunocytochemistry, labeled fibers were shown to constitute the majority of neuronal processes found in the intercellular region of the intermediate lobe. They were frequently seen to establish synaptoid contacts with endocrine cells.