IMMUNOLOCALIZATION OF B-50 (GAP-43) IN INTACT AND LESIONED NEUROHYPOPHYSIS OF ADULT-RATS

The persistence of high levels of B-50 in the adult brain is generally assumed to characterize neuronal systems capable of undergoing some f orm of plasticity such as axonal sprouting and regeneration, Since adu lt hypothalamo-neurohypophysial neurons are known to rapidly regenerat e after being transected, the present study was undertaken to determin e if such a capacity for regeneration could be related to the expressi on of this protein. Adult rats were killed by intraaortic perfusion of fixative either without lesion or at different delays after a surgica l transection of the hypophysial stalk. Electron microscopy and laser scanning confocal microscopy were used to examine the regenerating axo ns after single or double immunocytochemical labeling of vibratome sec tions for B-50 and for various neuronal markers characterizing differe nt types of neurohypophysial axons, In intact neurohypophysis, B-50 im munostaining was frequently associated with fibers immunoreactive to G ABA or to tyrosine hydroxylase, whereas it was not detected within pep tidergic neurohypophysial axons. In the lesioned neurohypophysis, B-50 was again frequently localized within axonal fibers immunoreactive to tyrosine hydroxylase or GABA. On the other hand, B-50 immunostaining was never detected within the numerous vasopressinergic or oxytocinerg ic axonal sprouts that regenerate all along the median eminence proxim al to the lesion. These data indicate that persistence of high levels of B-50 within the neurohypophysis of adult rats is a specific feature of catecholaminergic and/or GABA-ergic axons innervating this region and that, contrasting to other neuronal systems, B-50 is not involved in the remarkable capacity for regeneration exhibited by the vasopress inergic and oxytocinergic neurohypophysial axons. (C) 1995 Academic Pr ess, Inc.