INCREASED NUMBER OF UNMYELINATED AXONS IN OPTIC NERVES OF ADULT MICE DEFICIENT IN THE MYELIN-ASSOCIATED GLYCOPROTEIN (MAG)

We have recently demonstrated that the formation of myelin sheaths in the optic nerve of young postnatal mice deficient in the myelin-associ ated glycoprotein (MAG) is retarded when compared to age-matched wild- type mice. In the present study, we analyzed whether impaired myelinat ion of retinal ganglion cell axons is detectable in adult MAG mutants. In optic nerves of 2- and 9-month-old MAG-deficient mice, we observed a significantly increased number of unmyelinated axons compared to ag e-matched wild-type mice. At both ages, unmyelinated axons in optic ne rves of MAG mutants were of small caliber. The number of unmyelinated axons decreased significantly in 9-month-old MAG mutants when compared to 2-month-old MAG mutants, indicative of a slow and long-lasting mye lination of axons in the mutant. Our observations support the view tha t MAG is involved in the initiation of myelination in the CNS. (C) 199 7 Elsevier Science B.V.