Astrocytes and microglia show altered orientation in specific white-matter tracts in BTBR forebrain. Low-magnification coronal sections from representative (A, E, I) BTBR and (C, G, K) B6 mouse forebrain at the level at which misoriented glial fibers were visible. Gross anatomic changes included lateral displacement of the (A, I) hippocampus and (E) lateral septum. Rectangular area illustrates region highlighted at high magnification in adjacent panels: (A-D) glial fibrillary acidic protein (GFAP) immunostaining of a representative BTBR versus B6 mouse illustrated at high magnification in (B, D) the alveus at the level of the dorsal hippocampus. The orientation of GFAP-immunoreactive fibers in the alveus seemed prominently directed in the dorsolateral axis in BTBR brain. (E-H) GFAP staining in the cingulum of (F) BTBR versus (H) B6 mouse forebrain at the level of the striatum. The orientation of GFAP-immunoreactive fibers in the cingulum seemed prominently directed in the mediolateral direction in (F) BTBR compared with (H) B6 brain. GFAP-immunoreactive fiber density seemed to be increased in BTBR white matter in tracks neighboring the absent corpus callosum (compare B, F with D, H). (I-L) Ionized calcium-binding adaptor molecule (Iba)1 immunoreactivity in the alveus of (J) the BTBR versus (L) the B6 mouse. GFAP and Iba1 positive fibers were oriented dorsoventrally in (B, J) the BTBR brain rather than mediolaterally as seen in (D, L) the B6 brain. (J, L) Arrows are perpendicular to the directionality of Iba1-positive fibers. GFAP- and Iba1-immunoreactive cell bodies seemed qualitatively indistinguishable in terms of size, frequency and morphology between BTBR and B6 mice. Scale bars = (A, C, E, G, I, K) 1000 μm; (B, D, F, H, J, L) 25 μm.