Microglial cell reaction in the gray and white matter in spinal cords from jimpy mice. An enzyme histochemical study at the light and electron microscope level.

Jimpy is a genetic disorder which results in a severe hypomyelination in the central nervous system associated with a variety of astroglial and oligodendroglial abnormalities. In this study, we examined the morphology and distribution of microglial cells in spinal cord sections from jimpy and normal mice at 10-12 and 20-22 days postnatal using a specific microglial marker, the nucleoside diphosphatase staining. Compared to those of normal littermates, the spinal cords of jimpy mice showed an intense microglial cell reaction in white and gray matter, as revealed by quantitative analysis and light and electron microscope study. Microglial reactivity was apparent in all spinal cord areas, although it was more pronounced in white than in gray matter. The mean microglial densities in the jimpy white matter were about threefold (10-12 days) and fivefold (20-22 days) higher than in the normal, whereas in the gray matter, microglial density in jimpy was about 60% higher than in normal at both ages. Morphologically, microglial cells in the normal spinal cord showed a ramified appearance, similar in size and ramification pattern to those reported in other normal CNS areas. In contrast, microglial cells in the jimpy spinal cord showed a reactive morphology, characterized by a shortening and coarsening of their cell processes, swelling of their cell body and accumulation of lipid inclusions. Reactive microglial cells were found in close association with axons and oligodendroglial cells. The possible role of microglial cells in hypomyelination is discussed.