Neither Sel1L deficiency nor PERK inactivation altered the morphology of oligodendrocytes in the CNS. A–T, EM analysis showed that the morphology of oligodendrocytes and the morphology of the ER (insets) in oligodendrocytes appeared normal in the spinal cord of 3-, 5-, 6-, 10-, 16-, and 24-week-old WT mice, PERK cKO mice, Sel1L cKO mice, and double cKO mice. U–AG, CD11b immunostaining showed that the number of microglia was not significantly changed in the spinal cord of 3-, 5-, 6-, 10-, and 16-week-old Sel1L cKO mice compared with WT mice (U–Y,AA–AE,AG), but was significantly increased the spinal cord of 24-week-old Sel1L cKO mice compared with WT mice (Z,AF,AG; significant effect of group, F(1,6) = 122.3; significant effect of age, F(1.877,11.26) = 86.68; and significant group × age interaction, F(5,30) = 97.57). Scale bars: A–T, 1 μm; U–AF, 100 μm. N = 4 animals. Statistical analyses were done with a two-way ANOVA with a Bonferroni post-test. Error bars indicate SD. *p < 0.05.