MICROGLIAL CELL REACTION IN THE GRAY AND WHITE-MATTER IN SPINAL-CORDSFROM 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 mor phology and distribution of microglial cells in spinal cord sections f rom jimpy and normal mice at 10-12 and 20-22 days postnatal using a sp ecific microglial marker, the nucleoside diphosphatase staining. Compa red to those of normal littermates, the spinal cords of jimpy mice sho wed an intense microglial cell reaction in white and gray matter, as r evealed by quantitative analysis and light and electron microscope stu dy. Microglial reactivity was apparent in all spinal cord areas, altho ugh it was more pronounced in white than in gray matter. The mean micr oglial 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 tha n in normal at both ages. Morphologically, microglial cells in the nor mal spinal cord showed a ramified appearance, similar in size and rami fication pattern to those reported in other normal CNS areas. In contr ast, microglial cells in the jimpy spinal cord showed a reactive morph ology, characterized by a shortening and coarsening of their cell proc esses, swelling of their cell body and accumulation of lipid inclusion s. Reactive microglial cells were found in close association with axon s and oligodendroglial cells. The possible role of microglial cells in hypomyelination is discussed.