The expression of the Gal β-1,4-GlcNAc group in hippocampal microglia [a1–e1, Gal β-1,4-GlcNAc group; a2–e2, hippocampal microglia; a3–e3, co-localization; a1, a2, a3, the expression of the Gal β-1,4-GlcNAc group in hippocampal microglia of the normal group (n=6); b1, b2, b3, the expression of the Gal β-1,4-GlcNAc group in hippocampal microglia of the non-PQQ TBI group (n=6); c1, c2, c3, the expression of the Gal β-1,4-GlcNAc group in hippocampus microglia of the TBI+PQQ 5 mg/kg per day group (n=6); d1, d2, d3, the expression of the Gal β-1,4-GlcNAc group in hippocampal microglia of the TBI+PQQ 7 mg/kg per day group (n=6); e1, e2, e3, the expression of the Gal β-1,4-GlcNAc group in hippocampal microglia of the TBI+PQQ 10 mg/kg per day group (n=6); arrows, co-localization; a1–e3, ×400]. (S) Quantitative expression of the Gal β-1,4-GlcNAc group in hippocampal microglia [Normal, normal group (n=6); Injury, non-PQQ TBI group (n=6); 5, TBI+PQQ 5 mg/kg per day group (n=6); 7, TBI+PQQ 7 mg/kg per day group (n=6); 10, TBI+PQQ 10 mg/kg per day group (n=6)]. Results are shown as the mean±standard error of the mean (SEM) and represent three independent experiments [*p<0.05 versus Normal (n=6); #p<0.05 versus Injury (n=6); ##p<0.05 versus 7 mg/kg per day (n=6); PQQ, pyrroloquinoline quinine; TBI, traumatic brain injury; Gal β-1,4-GlcNAc, galactosidase β-1,4-galactosyltransferase N-acylsphingosine].