Myelin and glial membrane structures in the optic nerve of normal and jimpy mouse. A freeze-etching study.

In order to investigate the myelin and the glial cell membranes in the optic nerve of the mutant mouse "Jimpy," the method of freeze-etching was applied. The compact myelin lamellae and the first two glial membranes of the mutant, as compared to the normal mouse, show several abnormalities: absence of intramembraneous particles on the P-face, myelin lamellae separated by cytoplasmic layers, vesicular protrusions forming irregular invaginations, and elevations and tight junctions with a discontinuous, zigzag course. Some of these characteristics were found in the membrane of the oligodendroglia cell of the pathological animal, as well. The astrocytic membranes of both normal and Jimpy mice contain two types of gap junctions. The occurrence of one type seems to be increased in the mutant. Freeze-fractured internodal regions of the axolemma are not significantly different from those of normal animals.