Glucocorticoids are believed to increase hippocampal susceptibility to excitotoxic injury; however, the mechanisms by which steroids affect neurodegeneration are not well understood. Here, we utilized histological and biochemical methods to examine the interaction of corticosterone (CORT) and kainic acid (KA) on neurodegeneration, blood-brain barrier (BBB) disruption, and glial activation in the hippocampus of C57BL/6J mice. Male mice were implanted with 10, 35, or 100 mg/21 d release corticosterone pellets. After seven days, mice received an intraperitoneal injection of saline or 25 mg/kg kainic acid, were scored for seizures (Racine scale), and were allowed to recover for: 12 or 24 hours (histology); 0, 1, 3, 6, or 12 h (western blot); or 7 d (ELISA). Tissue was prepared for histological analysis of neurodegeneration using the cupric-silver stain, while microglia and astrocytes were visualized using immunohistochemical analysis of Iba-1 and GFAP, respectively. BBB disruption was quantified by western blotting using an anti-mouse IgG antibody. By 12 h following KA, damaged neurons were observed throughout all parts of the hippocampus, and activated microglia and astrocytes were observed in regions displaying neurodegeneration. A five-fold elevation of IgG in the hippocampus was evident six hours following KA injection. CORT alone did not induce seizures, produced no neuronal or BBB damage, and did not exacerbate the injury produced by KA. Pretreatment with CORT attenuated KA-induced neurodegeneration, glial activation, and BBB breach. Analysis of GFAP by ELISA revealed an elevation in protein levels following KA treatment (524.1 +/- 159.6%). CORT dosage and basal GFAP levels followed an inverse relationship (92.3 +/- 5.4%, 60.8 +/- 6.5%, 47.7 +/- 5.2%, of control, respectively). In CORT pretreated animals, KA-induced elevation of GFAP was attenuated (107.1 +/- 15.7, 94.1 +/- 22.4%, 53.4 +/- 7.2, of control, respectively). Considered together, these data suggest high dosages of corticosterone provide protection against KA-induced excitotoxicity.
The Toxicologist. Society of Toxicology 47th Annual Meeting and ToxExpo, March 16-20, 2008, Seattle, Washington