Figure 2.

Chronic EEG electrodes induce astrogliosis and glial scarring. A, Representative image of skull and dura immunostained for the endothelial marker, CD31. Inset, Higher-magnification image of an electrode burr hole where blood vessels show the continuing presence of intact dura. B, Representative images of brain–electrode interface in coronal slices 3, 20, and 40 d after implantation. Brains were stained for GFAP (top) and CD68 (bottom). C, GFAP and CD68 immunoreactivity intensities of brain tissue at the brain–electrode interface were analyzed in rectangular ROIs (dotted line) extending inward from the brain surface. D, Mice implanted for 3, 20, and 40 d showed increased GFAP immunoreactivities under the electrodes at all tissue depths (0–700 μm) compared with control mice. Inset, GFAP staining of cortical surface 3 d after surgery (SD; two-way ANOVA with Dunnett's multiple comparison; **p < 0.01, ***p < 0.001, ****p < 0.0001). E, Three days after surgery, CD68 expression was increased at all tissue depths analyzed. At 20 and 40 d after surgery, only the tissue 0–100 μm under the pial surface showed increased CD68 expression. Inset, CD68 staining of cortical surface 3 d after surgery (SD; two-way ANOVA with Dunnett's multiple comparison; ***p < 0.001, ****p < 0.0001).