Astrocytic activation plays a major role in homeostatic maintenance of the central nervous system in response to neuronal damage. To assess the reactivity of astrocytes in transient cerebral ischemia of the gerbil, we studied the levels of glial fibrillary acidic protein (GFAP) and its mRNA. GFAP mRNA increased by 4 h after carotid artery occlusion, reached peak levels by 72 h with a 12-fold increase over control and then started declining as early as 96 h postischemia. An examination of the specific regions of the brain revealed an increase in GFAP mRNA associated with the forebrain, midbrain, hippocampus and striatum. GFAP mRNA in the non-ischemic cerebellum however, remained expressed at constitutively low levels. Immunoblot analysis with anti-GFAP antibodies demonstrated a 2- to 3-fold increase in the protein after 24 and 48 h of reperfusion. Pretreatment with pentobarbital and 1-(5'-oxohexyl)-3-methyl-7-propyl xanthine (HWA 285), the drugs that have been shown to protect against ischemic damage, prevented the increase in GFAP mRNA in the cortex following ischemic injury. Forebrain ischemia also induced vimentin mRNA and protein quantities by 12 h of reperfusion in the cortex. The levels of c-fos and preproenkephalin mRNA increased rapidly within 1 h after ischemic injury, demonstrating a temporal difference in mRNA changes following ischemia. These results indicate that an increase in GFAP and vimentin, the two glial intermediate filament proteins in the area of the ischemic lesion may be associated with a glial response to injury.