Cultured neonatal rat oligodendrocytes elaborate myelin membrane in the absence of neurons.

We have utilized transmission electron microscopy to study oligodendrocyte-enriched cell cultures established from dissociated neonatal rat cerebra by the method of McCarthy and de Vellis [1980]. Cells were examined after 14 and 26 days in vitro. The overall morphology of the cells from cultures at both time periods was similar and consistent with previous reports of light (immature) oligodendrocyte fine structure. The cells contained an eccentrically located nucleus, prominent Golgi regions, numerous free ribosomes, and microtubules. Large numbers of processes with varying diameter were also observed. There was some indication of cytoplasmic maturation from the younger to the older cultures. The most important feature of the 26-day cultures was the large quantity of intercellular membranes which were shown to be continuous with oligodendrocyte processes. These membranes often exhibited the appearance of "loose myelin" and were therefore not normally compacted. Layers of membrane with the morphologic appearance of compact myelin were observed on an occasional oligodendrocyte perikaryon or process. This finding necessitates a reevaluation of the widely held theory that oligodendrocytes are not able to elaborate myelin in the absence of neurons.