Morphological evidence of alteration in myelinstructure with maturation.

The periodicity of the myelin sheath in glutaraldehyde carbohydrazide (GACH) embedded tissues from three 10-day-old and two 43-day-old mice was investigated with the electron microscope. The mean repeat period and number of repeats per fiber was measured in 31-89 fibers in the trapezoid bodies, olfactory tract and sciatic nerves. The mean period of the myelin sheaths in both the peripheral and the central nervous systems of the 10-day-old mice (15.1 +/- 0.07 nm (S.E.M.) and 13.4 +/- 0.09 nm respectively) are smaller (rho less than 0.001) than those of the adult mice (15.9 +/- 0.08 nm and 14.7 +/- 0.06 nm respectively). These differences may be related to the known differences in chemical composition of immature and mature myelin.