Serotonin-immunoreactive nerve fibers of the rat pituitary: effects of anticatecholamine and antiserotonin drugs on staining patterns

Serotonin-immunoreactive (5-HT-IR) nerve fibers observed in the pars nervosa of the rat pituitary gland were examined after treatment of animals with antiserotonergic or anti-catecholaminergic drugs. p-Chlorophenylalanine, (PCPA), an inhibitor of 5-HT synthesis, eliminated staining in both areas of the pituitary gland. p-Chloroamphetamine (PCA), a serotonin neurotoxin, did not produce a significant change in 5-HT-IR from control tissue. Unexpectedly, 6-hydroxydopamine (6-OHDA), a catecholamine neurotoxin, eliminated 5-HT staining in the pars intermedia, but not in the pars nervosa. These observations suggest that 5-HT present in fibers innervating the intermediates and neural lobes is synthesized in axons locally, or is taken up into fibers from extrinsic sources. In addition, catecholamines and 5-HT may co-exist in nerve terminals of both lobes of the pituitary gland.