Effect of lipopolysaccharide and stress on the number of activated microglial cells in the substantia nigra. Quantification of changes on the reactive microglial population in the substantia nigra at the end of the treatments. Results are mean ± SD of four independent experiments expressed as OX-6-positive cells/mm2. P < 0.001 by one-way analysis of variance followed by the least significant difference post hoc test for multiple range comparisons: a, compared with vehicle (V); b, compared with stress (S); c, compared with lipopolysaccharide (L); d, compared with stress + lipopolysaccharide (SL). SLR, Lipopolysaccharide injected into stressed animals treated with RU486 (mifepristone (11β-[p-(dimethylamino)phenyl]-17β-hydroxy-17-(1-propynyl)estra-4,9-dien-3-one)).