INNERVATION OF THE RAT ANTERIOR AND NEUROINTERMEDIATE PITUITARY VISUALIZED BY IMMUNOCYTOCHEMISTRY FOR GROWTH-ASSOCIATED PROTEIN GAP-43

Immunocytochemical localization of the neuronal growth associated prot ein GAP-43 revealed a dense axonal plexus throughout the neurointermed iate lobe of the rat pituitary. These axons were fine, presumably mono aminergic fibers, whereas magnocellular neurosecretory axons did not a ppear to contain detectable GAP-43. These experiments also revealed th e presence of an extensive nerve plexus within the anterior lobe. Fine beaded fibers were present throughout the parenchyma of the anterior lobe, and punctate staining suggestive of nerve terminals was seen sur rounding numerous endocrine cells. Nerve fibers did not appear to cros s directly between the intermediate and anterior lobes, but rather ent ered the anterior lobe directly from its margins or in association wit h blood vessels. Preabsorption of antisera with GAP-43 purified from n eonatal rat brain completely eliminated immunoreactivity. These findin gs confirm the existence of a direct innervation of the anterior pitui tary of the rat; moreover, the presence of GAP-43 in these fibers sugg ests that they may be capable of growth and terminal reorganization in the adult animal.