Even in culture, oligodendrocytes myelinate solely axons.

Cerebral hemispheres from mouse embryos at 15 days of gestation were dissociated and maintained in culture for several weeks in a medium which permitted homochronic and homotypic oligodendrocytes and neurons to interact in the presence of other central nervous system cells. After 13-14 days in culture a few oligodendrocytes changed from highly branched, "sun-like," nonmyelinating cells to sparcely branched myelinating cells. The number of fibers myelinated per oligodendrocyte ranged from 1 to 10, similar to that described previously in vivo in the corpus callosum. When an oligodendrocyte began to myelinate, it immediately myelinated a maximum number of fibers, suggesting that the number of axons to be myelinated by the oligodendrocyte was predetermined. When only one fiber was in the vicinity of a myelinating oligodendrocyte, whorls of myelin-like figures were seen at the tip of oligodendrocyte processes that had not reached an axon. Myelinated fibers were unambiguously identified as axons both by immunostaining and by electron microscopy. Myelin was not observed around astrocyte processes or around dendrites. The exclusive myelination of axons suggests the existence of a specific axonal recognition signal which attracts oligodendrocyte processes. IMAGES:

将妊娠15天的小鼠胚胎大脑半球解离后，置于可容纳其他中枢神经系统（central nervous system, CNS）细胞的培养基中培养数周，该培养体系可使同时相、同型的少突胶质细胞（oligodendrocytes）与神经元（neurons）发生相互作用。培养13-14天后，少量少突胶质细胞从高度分支的“太阳状”非髓鞘形成细胞，转变为分支稀疏的髓鞘形成细胞。单个少突胶质细胞所髓鞘化的神经纤维数量介于1至10之间，这与此前在体内胼胝体（corpus callosum）中报道的结果一致。当少突胶质细胞启动髓鞘化过程时，会立即达到可髓鞘化纤维的最大数量，这表明该细胞所要髓鞘化的轴突（axon）数量是预先确定的。当髓鞘形成性少突胶质细胞附近仅存在一条神经纤维时，未接触轴突的少突胶质细胞突起末端可观察到髓鞘样结构的螺旋状聚集物。通过免疫染色（immunostaining）与电子显微镜（electron microscopy）检测，可明确将髓鞘化纤维鉴定为轴突。未在星形胶质细胞（astrocyte）突起或树突（dendrite）周围观察到髓鞘结构。仅对轴突进行髓鞘化这一现象，提示存在一种可引导少突胶质细胞突起的特异性轴突识别信号。图像：