The myelin-deficient rat mutant: partial recovery of oligodendrocyte maturation in vitro.

The morphological and immunocytochemical identification and characterization of the myelin-forming cell, the oligodendrocyte, have defined a model system for developmental studies. The myelin-deficient (md) rat mutant lacks myelin in the central nervous system and fails to express the normal developmental increase in oligodendroglial and myelin markers, apparently as a consequence of a point mutation in the proteolipid protein gene. In the present work, we compared the developmental pattern of primary glial cultures derived from newborn md rat brains to those derived from wild-type animals. Brain cell suspensions were prepared from each rat pup and cultured separately. We found by immunocytochemical and enzymatic analyses for the various markers that the developmental cascade of oligodendroglial marker expression is delayed, oligodendrocytes failing to mature compared to normal cultures. However, a partial recovery of marker expression was observed in md-derived cultures as compared to development previously reported in the intact md animals. We suggest that the partial recovery of the sequential expression of oligodendroglial markers may be due to a supportive environment provided to the oligodendrocyte progenitor cell (1) by tissue culture conditions or (2) by the absence of the blood-brain barrier in contrast to its presence in the intact animal.