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Basic fibroblast growth factor (bFGF; FGF-2) has potent trophic effects on developing and toxically impaired midbrain dopaminergic (DAergic) neurons which are crucially affected in Parkinson's disease. The trophic effects of FGF-2 are largely indirect, both in vitro and in vivo, and possibly involve intermediate actions of astrocytes and other glial cells. To further investigate the cellular and molecular mechanisms underlying the restorative actions of FGF-2, and to analyse in more detail the changes within astroglial cells in the MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine)-lesioned striatum, we have studied striatal expression and regulation of connexin-43 (cx43), the principal gap junction protein of astroglial cells, along with the expression of glial fibrillary acidic protein (GFAP), FGF-2, and functional coupling. Our results show an immediate, yet transient increase in cx43 mRNA, and a sustained increase in FGF-2 mRNA, GFAP-positive cells, and cx43-immunoreactive punctata following the MPTP lesion, without any induction of functional coupling between astrocytes and other glial cells as revealed by dye coupling of patched cells. Unilateral administration of FGF-2 in a piece of gelfoam caused a further increase in cx43-positive punctata immediately adjacent to the implant, which was more pronounced than after application of a gelfoam containing the non-trophic control protein in cytochrome C. These changes were parallelled by a small increase in cx43 protein determined by Western blot, but not by alterations in the coupling state of cells in the vicinity of the gelfoam implant. Although our data indicate that MPTP and exogenous FGF-2 may alter expression and protein levels of cx43, they do not support the notion that increases in cellular coupling may underly the trophic and widespread actions of FGF-2 in the MPTP-model of Parkinson's disease. © 1996 Wiley-Liss, Inc.

Fibroblast growth factor-2 (FGF-2), locally administered in gelfoam to the striatum of mice treated with the neurotoxic drug 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), has restorative and neuroprotective effects on dopaminergic neurons and associated striatal transmitter systems. Most of the beneficial alterations are apparently indirect. FGF-2 must therefore act through a series of cellular and molecular intermediate steps, which have not been explored. We have previously shown that FGF-2 does not significantly affect the astroglial reaction at the time, when the neuroprotective effect of FGF-2 reaches a peak (Day 11). In this study we have investigated the effect of FGF-2 at earlier time points after MPTP treatment. We report now that as early as 6 h after administration of the gelfoam containing either FGF-2 or control protein, FGF-2 immunoreactivity disappears from astroglial nuclei, while appearing in small ramified GFAP- and S-100-negative cells, most likely microglia. At 18 h, numbers and staining intensities of GFAP-ir astroglial cells are greater in FGF-2- than in cytochrome C-treated animals. At this time FGF-2-ir reappears in astroglia nuclei of cytochrome C-treated animals, but remains undetectable in the striatum carrying the FGF-2-containing gelfoam. Ramified GFAP/S-100-negative presumed microglial cells are now intensely ir for FGF-2. Signs of an FGF-2-mediated astrogliotic reaction are very pronounced at 18 h and 2 days, but no longer at 11 days, when the astrogliosis reaction has become equally strong in FGF-2- and cytochrome C-treated striata. Our results suggest that administration of FGF-2 to the MPTP-lesioned striatum has early effects on astro- and presumed microglia cells, notably on the nuclear FGF-2-ir of astrocytes. These changes may be involved in mediating the neuroprotective effects of FGF-2 in the MPTP-model of Parkinsonism.