Rat brain oligodendrocytes do not interact selectively with axons expressing different calcium-binding proteins

A single oligodendrocyte may endow ten to twenty vicinal axons with internodal segments, but its radial domain is neither exclusive of processes from other like cells nor are all nerve fibres within this zone myelinated. Whether oligodendrocytes are able to discriminate between axons on the basis of chemical or electrophysiological differences, or whether the tactic response is random, has yet to be established. In order to shed some light on this process, we investigated the ensheathment, by single oligodendrocytes, of axons distinguished on the basis of their calcium-binding protein complexion. Rat brain oligodendrocytes were visualized either with the Rip-antibody or by intracellular injection of Lucifer Yellow; subclasses of axons were immunolabelled with antibodies against one of the two calcium-binding proteins parvalbumin or calretinin. Individual oligodendrocytes did not exhibit exclusivity with respect to their preferment for axons containing calcium-binding proteins, associations with both non-immunoreactive, as well as with parvalbumin- or calretinin-positive ones, being encountered.