Ultrastructural characteristics of vacuoles in the corpus callosum of TgPAC-Notch3
mice at 20 months of age. (A) Typical vacuole (star) in the innermost layer of the myelin sheath. The vacuole separates the axon from its myelin sheath (black arrowheads) and contains multiple aberrant myelin sheets (arrows). Notice the thin myelin sheet (empty arrowhead) at the interface between the axon and the vacuole. (B) Longitudinal section of a myelinated fiber containing a vacuole in the innermost layer of the myelin sheath. (C) Typical vacuole (star) in the outermost layer of the myelin sheath. The vacuole is delineated by a thin rim of myelin (empty arrowheads) and contains occasional myelin debris (arrows). (D) Shown are 3 atypical intracellular vacuoles (orange arrows) located in an astrocytic endfoot (delineated by a white dashed line). Notice the presence of a small typical intramyelinic vacuole (star) in the same field. (E) Diagram of the distribution of vacuole location revealing a large preponderance of intramyelinic vacuoles (n = 4 TgPAC-Notch3R169C). (F) Diagram of the % of vacuoles developed in the innermost versus outermost layers of the myelin sheath showing a large majority of the innermost lesion type (n = 4 TgPAC-Notch3R169C). (G) Scattergram of g-ratios in relation to axonal diameters showing no difference between control (n = 4) and TgPAC-Notch3R169C mice (n = 4). Scale bar represents 1 μm (A), 0.5 μm (B), 1.3 μm (C) and 1.75 μm (D).