It is well established that proliferation of progenitor cells persists within the hippocampal dentate gyrus (DG) and the subventricular zone of the lateral ventricle (SVZ) in the adult brain. The aim of the present study was to determine whether the rate of cell proliferation within these germinative zones could be correlated to the occurrence of a particular glial environment. The cell proliferation marker bromodeoxyuridine (BrdU) was administrated to rats under different physiological and experimental conditions known to modify the rate of progenitor cell proliferation. Within both germinative zones, BrdU-labeled nuclei were associated with cell bodies immunostained for the neuronal marker polysialylated neural cell adhesion molecule, but not for the glial markers glial fibrillary acidic protein (GFAP) or vimentin (VIM). In all the rats examined, however, proliferating (BrdU-labeled) cells always exhibited close relationships with immature-like astrocytes that expressed both GFAP and VIM. There was a dramatic decrease of cell proliferation in the DG from both the aged rats and the corticosterone-treated adult rats that was correlated with a decreased expression of vimentin by the astrocytes present in this region. In contrast, both cell proliferation and vimentin expression were only slightly affected in the SVZ from these two treatment groups. Conversely, after either adrenalectomy or a surgical lesion through the lateral hippocampus, the increase in cell proliferation observed in the DG was correlated to the occurrence of an increased number of GFAP and VIM double immunostained structures in these regions. All together, these data suggest that immature-like astrocytes present in the germinative zones may provide a microenvironment involved in sustaining the proliferation of progenitor cells.
Copyright 2001 Wiley-Liss, Inc.