MYELINATION OF THE CEREBRAL COMMISSURES OF THE HAMSTER, AS REVEALED BY A MONOCLONAL-ANTIBODY SPECIFIC FOR OLIGODENDROCYTES

Myelination of the cerebral commissures of the hamster was studied by immunostaining with a monoclonal antibody (Rip) specific for oligodendrocytes. Immunostained, preensheathing cells were first observed' in the anterior commissure on P6 (P1 = day of birth). By P8, immunopositive oligodendrocytes and myelinated fibers clustered around some of them were detected within the posterior limb of the anterior commissure, ventrally at the rostral half of the callosum, and in the hippocampal commissure. On P12. all the commissures had myelinated fibers throughout their extent. but the callosum and the hippocampal commissure exhibited higher densities of myelinated fibers rostrally. Between P15 and P22, the pattern of myelination approached that of the adult. In the context of other developmental events. myelination of the corpus callosum and of the anterior commissure is a late event, occurring predominantly after stabilization of axon number either at the end of the progressive accretion of axons, as in the anterior commissure. or after the selective elimination of callosal projections.