Structural effects of external media on isolated myelinated axons

Myelinated axons were isolated from the sciatic nerve of Xenopus laevis by desheathing and teasing, and were mounted for short-term light microscope observation in different media. Fibres mounted in a conventional physiological saline showed a tendency to gross structural changes, including collapse of axons and separation of the axon from the myelin sheath. With isotonic media based on 120mM potassium aspartate, or 120mM potassium glutamate, structural stability and axoplasmic function (assessed by persistence of particle transport) were well maintained. The speeds of retrograde particle transport in fibres immersed in potassium aspartate or potassium glutamate medium ranged from 0.05 to 3.15 micron/sec with mean speeds of 1.05 and 1.2 micron/sec. Transport persisted for up to 3 hr. Isotonic media based on amino acids but lacking K+ or Na+ were unsatisfactory short-term culture media and destabilized myelin structure. Inclusion of 60 mM KCl in the medium reduced structural disruption and allowed particle transport to persist.