Glial fibrillary acidic protein messenger RNA and glutamine synthetase activity after nervous system injury.

The level of the mRNA for glial fibrillary acidic protein (GFAP), the major protein of the intermediate filaments of astroglial cells, and the activity of glutamine synthetase (GS), an enzyme selectively localized in astrocytes, were measured at different times after a unilateral mechanical lesion in the rat cerebral cortex. A rapid and early increase (6 hours post-lesion) in GFAP mRNA was observed; GFAP mRNA level reached a peak at 1-3 days and then decreased. Moreover, an astrocytic activation in cortical zones far from the injury site and in the contralateral hemisphere was detected. No change of GS activity was observed in the same model of brain injury, showing that this astroglial marker is not modified during the reactive gliosis obtained with this experimental model. GFAP mRNA has also been detected in the rat sciatic nerve; however, its level was not modified after nerve transection, suggesting a different regulation of GFAP expression in the peripheral nervous system.