OLIGODENDROCYTES IN FEMALE CARRIERS OF THE JIMPY GENE MAKE MORE MYELIN THAN NORMAL OLIGODENDROCYTES

The female carrier of the jimpy (jp) gene is a model system to study t he plasticity of neuroglial cells and the mechanisms they use to compe nsate for a temporary deficit in myelin. Myelin in the female carriers is reduced 30-40% during the first postnatal month but is normal in a dults. We hypothesized that the number of oligodendrocytes (OLs) in th e female carriers is increased, based upon previous data showing OL pr oliferation is increased but the number of dying OLs is only slightly elevated in development. To test this hypothesis, antibodies to carbon ic anhydrase (CA)II, an OL-specific marker, were used to quantify the number of OLs in the spinal cords of 1-month-old and adult female carr iers. Contrary to expectations, the number of OLs is significantly red uced in the dorsal funiculus and grey matter by 21% in adult female ca rriers compared to controls. A reduction of lesser magnitude is presen t in the 1-month-old animals. Electron microscopic montages prepared f rom normal and carrier dorsal funiculus were used to count total numbe rs of glia. Ultrastructural quantification shows a similar reduction i n the number of OLs and confirms the validity of the CAII immunostaini ng as a means to quantify OLs. These data show that there are 21% fewe r OLs in the central nervous system (CNS) of adult female carriers but normal amounts of myelin. Presumably, some OLs in the carrier CNS are maintaining more myelin than their counterparts in normal CNS would. These findings demonstrate that (1) a reduction in number of OLs does not necessarily involve a reduction in the amount of myelin, and (2) O Ls have considerable flexibility in the amount of myelin they can make . (C) 1995 Wiley-Liss, Inc.