Heterogeneous morphology and tracer coupling patterns of retinal oligodendrocytes

The present study characterizes the morphology and tracer coupling patterns of oligodendrocytes in the myelinated band of the rabbit retina, as revealed by intracellular injection of biocytin or Lucifer yellow in an isolated superfused preparation. Based on the observed heterogeneity in morphology, we have grouped the presumptive oligodendrocytes into three categories termed 'parallel', 'stratified' and 'radial'. Most parallel oligodendrocytes were tracer coupled to nearby oligodendrocytes and astrocytes, whereas the stratified and radial oligodendrocytes rarely showed coupling. We conclude that the different categories of oligodendrocytes may be stages in a developmental series, with radial oligodendrocytes being premyelinating cells, parallel oligodendrocytes being mature myelinating cells and the stratified cells representing a transition between these categories.