The expression of S100β and glial fibrillary acidic protein (GFAP) was analyzed following bilateral injection of kainic acid (KA), a glutamate derivative, into the CA3 region of the adult rat hippocampus. This treatment produces a progressive degeneration of the pyramidal neurons of the hippocampus while sparing the granule cells of the dentate gyrus which undergo sprouting of their axons in the supragranular layer. Messenger RNA and protein levels were measured, by Northern blot and ELISA, in the hippocampus of lesioned and sham-operated rats 1, 7, and 30 days after KA injection. A significant increase of GFAP and its mRNA was demonstrated at each time point, whereas S100β mRNA levels were significantly enhanced only 30 days after the KA injection and the levels of S100β protein remained unchanged at all time points. However, when analyzed by immunohistochemistry the S100β showed clear changes in its expression and distribution depending on the region considered. One month after KA injection, S100β immunoreactivity was considerably reduced in the stratum radiatum of CA3 region, but there was increased S100β immunoreactivity in the stratum moleculare. In particular, a notable band of S100β positive, hypertrophic astrocytes appeared in the supragranular layer of the dentate gyrus where the sprouting of mossy fiber collaterals was detected by Timm's staining. These data show for the first time that an increase in S100β expression in subpopulations of reactive astrocytes may be involved in the structural reorganization of the hippocampus following KA-induced neurodegeneration. (C) 2000 Academic Press.
- Axonal sprouting
- Glial fibrillary acidic protein (GFAP)
- Kainic acid
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