Oligodendroglial structures and distribution shown by carbonic anhydrase immunostaining in the spinal cords of developing normal and shiverer mice

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Abstract
The spinal cords of young and adult normal and dysmyelinating mutant (shiverer) mice were immunostained with anticarbonic anhydrase to investigate (1) the distribution of oligodendroglial populations into the gray- and white-matter regions in the developing normal and mutant animals; (2) the morphology of oligodendrocytes and their processes at the light microscopic level in gray matter and white matter; and (3) the apparent gliosis in the gray matter, as well as the white matter, of the mutants. Immunocytochemistry and enzyme assays revealed consistent increases in carbonic antigenicity and specific activity in controls and mutants between the ages of ˜ 15 days and ˜ 60 days. As shown previously in adult animals, oligodendroglia in larger than normal proportions were situated at the periphery of the “white-matter” columns, as compared to gray matter, in the shiverers, with, however, significant numbers of oligodendroglia also occurring in gray matter. In normal white matter, at all ages, the oligodendroglia were heterogeneous with respect to shapes, configuration of processes, and intensity of carbonic anhydrase immunostaining. In the shiverer “white matter” the oligodendrocytes were smaller than normal, and their shapes and arrangement were relatively irregular. In the normal gray matter short oligodendroglial processes appeared to be associated with neuronal perikarya, and those processes were more pronounced at ˜ 90 days than at ˜ 20 days of age. Background staining in normal gray matter suggested that oligodendroglial processes were, in addition, tightly wound around many axons. In shiverer gray matter the oligodendrocytes were smaller, and their processes appeared to be wrapped more loosely around smaller numbers of conspicuous axons and to be associated less frequently with neuronal perikarya. This finding suggests that the deficiency in the myelin basic protein in the mutant may affect interaction betwen oligodendrocytes and neurons in the gray matter as well as in the white matter. The astrocytic “marker,” glial fibrillary acidic protein, was detected in gray and white matter of shiverers as young as 16 days, and the differences from carbonic anhydrase localization supported the conclusion that the processes enwrapping axons in the shiverer mouse CNS are derived from oligodendrocytes, not astrocytes.