Astrocytal changes in the white matter of Jimpy mice: immunohistochemistry using antisera to glial fibrillary acidic protein.

Immunohistochemistry using antisera to glial fibrillary acidic protein (GFAP) was performed to observe astrocytal changes in the white matter of myelin-deficient Jimpy mice. In wild-type controls, astrocytes stained with the GFAP immunoreaction appeared in the cerebellar medulla by postnatal day 3 and in the corpus callosum by postnatal day 6. The immunoreactivity gradually intensified with age to reach a peak of the GFAP level around postnatal day 12. With the progress of myelinogenesis, GFAP positive astrocytes decreased in number and became sparse in the white matter. On the other hand, the white matter of Jimpy mutant mice revealed intensified GFAP immunoreactivity, corresponding to a numerical increase in astrocytes and an enlargement of their cytoplasm. This condition continued from postnatal day 12 up to the end of life. Such astrocytes made up a dense framework with thickened processes in the non-myelinated white matter, where oligodendrocytes were few. Under the electron microscope, an accumulation of gliofilaments and glycogen particles was apparent in the enriched astrocytal cytoplasm. Immunostaining was observed not only on gliofilament bundles but also rough endoplasmic reticulum and cytoplasmic matrix. The present results demonstrate that astrocytal hypertrophy and hyperplasia occur in the entire white matter of Jimpy mice.