Thin sections of stretch-injured optic nerve at 12 h survival. Tissue was processed using the pyroantimonate technique. (a) At lower magification of longitudinal/oblique sections of nerve fibers nodal structure appears normal (center) except for some disruption of the paranodal myelin. In the larger caliber nerve fibers, however, mds now extend either inside (myelin intrusions, mi) or outside (external protrusions, ep) the thickness of the myelin sheath and contain pyroantimonate precipitate. Myelin discontinuities/intrusions/extrusions are more numerous in larger than in the smaller fibers (within the oval profile above the node of Ranvier). The greater circumferential disruption formed by md, mp and me is obvious in transverse sections of nerve fibers (b) and are more numerous and extensive within the myelin sheath of larger fibers. The axons have an irregular cross-section and a number of periaxonal spaces (pa) occur between the axon and the myelin sheath. Mitochondria within the axoplasm either contain aggregates of pyroantimonate precipitate (arrow) or have a central lacuna (double arrow). The axoplasm of the nerve fibers contains closely spaced microtubules and neurofilaments which form spiral arrays. Magnification (a) 7500×; (b) 23,450×.
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