Figure 6.

Agenesis of the corpus callosum and formation of Probst bundles in the brain of MAP1B-deficient mice. (a, c, e, g, and i) Frontal sections through the cerebral white matter and corpus callosum (CC) of a normal wild-type mouse brain, showing normal architecture of myelinated fiber tracts including the corpus callosum (a, c, and e, blue), axons (g, dark brown), and astrocytes (i, brown). (b, d, f, h, and j) Corresponding brain region of a homozygous MAP1B-deficient mouse. The corpus callosum is absent. The cerebral white matter ends medially in a thick bundle of myelinated fibers (*Probst bundle). Within the deeper layers of the cortex, thick bundles of myelinated axons are visible (arrowheads). Despite the massive structural changes in the brain tissue, there is no increase in reactive astrocytes. CX, cerebral cortex. (a–d) Luxol fast blue myelin stain; myelinated fiber tracts such as the corpus callosum are stained blue, areas of grey matter are stained red, 40×. (e and f) Luxol fast blue myelin stain, 120×. (g and h) Bielschowski silver impregnation; axons within fiber tracts are stained black, areas of grey matter reveal light brown staining, 120×. (i and j) Immunocytochemistry for glial fibrillary acidic protein; astrocytes containing glial fibrillary acidic protein are stained brown. Cellular nuclei of the tissue are counterstained with hematoxylin blue, 120×.