Reactive gliosis induced by MK-801 in the rat posterior cingulate/retrosplenial cortex: GFAP evaluation by sandwich ELISA and immunocytochemistry.

MK-801 (dizocilpine maleate) and certain other related antagonists of the N-methyl-D-aspartate receptor produce vacuolization and necrosis of neurons in the posterior cingulate/retrosplenial (PC/RS) cortex of rats. Neuronal necrosis initiates an astrocytic and microglial reaction. The present studies evaluated the astrocyte response with a sandwich format enzyme-linked immunosorbant assay (ELISA) for glial fibrillary acidic protein (GFAP), the major intermediate filament protein in astrocytes. In all cases, Sprague Dawley rats (age 60-70 days) were given single subcutaneous doses of MK-801 and detergent-based sample homogenates were subjected to GFAP ELISA. Initially, female rats receiving vehicle or 0.1, 1.0, or 10 mg/kg MK-801 were sacrificed on 3, 5, 9, or 16 days postdose (DPD). Fresh brain samples included PC/RS (target) and frontal (non-target) cortices. A significant, dose-dependent increase in GFAP occurred in the PC/RS cortex (highest in the 10 mg/kg group at 9 DPD). A second study with both sexes (10 mg/kg; 9 DPD) showed increased GFAP, but there was no difference by sex. Finally, punch samples from PC/RS, occipital, temporal, and entorhinal cortex (females; 10 mg/kg; 9 DPD) revealed a highly significant increase in GFAP confined to the PC/RS cortex. The localized increase in GFAP was confirmed by immunocytochemistry. These biochemical and immunocytochemical data demonstrate a localized astrocytic response to neuronal necrosis that is restricted to the PC/RS cortical target area. Our findings are consistent with previous data showing that chemical-induced injury of the CNS results in dose- and time-dependent increases in GFAP that are restricted to the sites of damage.