INDICATORS OF GLIAL ACTIVATION AND BRAIN OXIDATIVE STRESS AFTER INTRAVENTRICULAR INFUSION OF ENDOTOXIN

Glial activation and oxidative stress are both consequences of brain a ging. To investigate whether glial activation causes oxidative stress or not, the immune activator, lipopolysaccharide (LPS), was intraventr icularly injected into the rat brain. The expression of candidate gene s were examined by in situ hybridization histochemistry (ISHH) combine d with immunohistochemistry for glial markers over a period of time up to 24 h after the LPS injection. The mRNA for glial fibrillary acidic protein (GFAP) was elevated around the injection site by 2 h, and the volume of elevated expression spread to the entire brain after 6 h, w ith higher levels present in the injected hemisphere. The level of ind ucible isoform of nitric oxide synthase (i-NOS) mRNA increased in a pu nctate-like pattern in the region of the injection by 6 h and this res ponse spread to the entire brain after 12 h. These results indicate th at the glia are activated for at least 24 h after a single LPS injecti on. The mRNAs for a heat-shock protein (HSP70) and for the manganese-d ependent superoxide dismutase (Mn-SOD) were elevated in the ipsilatera l hemisphere as early as 2 h post-injection, but these responses subsi ded nearly to basal levels by 4 h. These levels of mRNAs for these gen es increased again after 6 h of the LPS injection; thus, the earlier i ncreases of the messages appeared to be associated with the survival s urgery procedure. With microautoradiographic analysis, scattered OX-42 positive cells expressed i-NOS mRNA after 6 h post-injection, but ele vation of Mn-SOD mRNA was not detected in either microglia or astrocyt es at any time point examined. The level for Cu/Zn-SOD mRNA did not al ter at any time point. The beta-amyloid precursor protein (beta APP) m RNAs were elevated beginning at 6 h. These results indicate that chron ic glial activation leads to a condition of oxidative stress in the br ain. The data also suggest that LPS injection could be used to study t he effects of chronic glial activation on the survival of neuronal pop ulations that could be at risk from oxidative stress. (C) 1998 Elsevie r Science B.V. All rights reserved.