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

To analyze whether the reorganization of the rat median eminence after hypo physectomy might be related to changes in glial fibrillary acidic protein ( GFAP)- and cellular proliferation, the distribution of cells immunoreactive for GFAP and the proliferation rate of such cells were analyzed at 20, 40 and 60 days posthypophysectomy. For this study, four rostro-caudat regions of the median eminence were differentiated: the retrochiasmatic, preinfundi bular, infundibular and postinfundibular regions. In each of these regions, three layers were studied: the ependymal, the internal and the external. A t 20 and 40 days after hypophysectomy, significant increases in cellular pr oliferation affecting all three layers studied in the preinfundibular and i nfundibular regions were found. At the same time points, increases in GFAP expression were also observed. However, after 60 days, GFAP and proliferati ve cellular nuclear antigen (PCNA) expression decreased. Although variation s of PCNA and GFAP levels were evident, no colocalisation of PCNA and GFAP was found in the cells of the median eminence in untreated or hypophysector nized rats when sections were analyzed by double immunohistochemical staini ng. Our results suggest that reorganization of median eminence involves alt erations (or modulation) of GFAP-immunoreactive cells together with a proli feration of cells that are not GFAP-immunoreactive. This study also demonst rates that this reorganization is completed within the first two months aft er hypophysectomy.