E-PTA stains oligodendroglial surface membranes and microtubules in optic nerves during myelination

Aldehyde fixed Xenopus tadpole and frog optic nerves were stained en bloc with ethanolic phosphotungstic acid (E-PTA). During rapid myelination, intense staining was observed on cytoplasmic faces of paranodal terminal loops and loosely wrapped oligodendroglial membranes found along inner and outer surfaces of compact myelin sheaths. Oligodendroglial microtubules also were heavily stained. Where stained cytoplasmic faces fused to form a lamella of compact myelin, the intense staining was reduced to a thinner, fainter line. In optic nerves of adult frogs, the staining was less dense but the pattern was similar. The staining distribution and available histochemical evidence indicate that E-PTA stains positively charged proteins non specifically. Since myelin basic protein is found in oligodendroglia during myelination, we suggest that it is being stained by E-PTA while being transported along microtubules to sites where it is inserted into developing myelin lamellae.