Characterization of GFAP expression and cell proliferation in the rat median eminence following hypophysectomy

Abstract

To analyze whether the reorganization of the rat medi an emin ence aft er hypophysectomy might be related to changes in gli al fibrill ary ac idi c protein (GFAP)- and cellular prolife ration, th e distribution of cells immunoreactive for GFAP and the prolife ration rate of such cells were analyzed at 20, 40 and 60 days posthypoph ysec tomy. Fo r this stud y, four rostra -ca ud al regions of the medi an eminence we re diffe renti ated: the retroc hi as mati c, preinfundibul a r, infundi bul ar and postinfundibul ar regions. In each of these regions, three layers were studied: the ependymal, the internal and the ex tern al. At 20 and 40 days aft er hypoph ysec tomy, significant increases in ce llular proliferation affecting all three laye rs studi ed in th e pre infundi bul a r a nd infundibul ar regio ns we re fo und . At the same time po ints, in c reases in GFAP ex pr essio n we re a lso obse rved . Howeve r, a ft e r 60 days, GFA P a nd proliferative ce llular nuclear antigen (PCNA) expression dec reased. Although va ri ati ons of PCNA and GFA P levels were ev id ent, no coloca lisa ti on of PCNA and GFAP was fo und in the cells of the medi an eminence in untreated or hy pophysectomized rats when sections we re analyzed by double immunohistochemica l staining. Our results suggest that reorgani zation of med ian eminence in vo lves alt e rati o ns (o r modul ati o n) o f GFA Pimmunoreacti ve ce lls together with a proliferation of cells that are not GFAP-immunoreactive. This study also demonstrates that this reorgani zation is completed within the fi rst two months afte r hypophysectomy.