Propionate or butyrate reduced microglial activation in germ‐free (GF) rats. A) Experimental design of the propionate and butyrate treatments. B) Serum concentrations of propionate and butyrate in GF, GF‐Pro, and GF‐But rats (n = 6). Kruskal–Wallis test with Dunn's multiple comparison post hoc test. C) Representative images of Iba‐1‐stained microglia and the microglia count in the anterior cingulate cortex‐rostral (ACC‐R), ACC‐caudal (ACC‐C), dorsal hippocampus (DH), and spinal dorsal horn L6‐S1 of rats detected by immunofluorescence staining (n = 6). Scale bar = 50 µm. Microglia, green; nuclei, blue. One‐way ANOVA with Tukey's post‐hoc test. D) Representative three‐dimensional reconstructions of Iba‐1‐stained microglia and morphological parameters of microglia in the ACC‐R, ACC‐C, DH, and spinal cord (n = 6). Scale bar = 10 µm. One‐way ANOVA with Tukey's post‐hoc test. *, p < 0.05; **, p < 0.01; ***, p < 0.001.