Myelin in the developing human cerebrum.

In order to ascertain the true composition of human myelin at the earliest stages of development and to shed some light on the controversial results published to date, the lipid and protein composition of myelin from unfrozen cerebrum of very young infants was compared to the values obtained later in development and to those obtained by other investigators using frozen human brain. The effect of 3 different procedures of myelin isolation, as well as varying periods of storing the brain in frozen state, were tested on the final composition of myelin. All myelin preparations were of a very high degree of purity, and the lipid composition changed very little either with age or by varying the method or the time of storage of the brain. Protein composition, on the other hand, changed drastically after freezing the brain for increasing periods, and the percentage of myelin basic protein (MBP) decreased to one-third of its original value after about a year of brain storage. However, when myelin was isolated from unfrozen brain immediately after autopsy, very high values of MBP were obtained, even in newborn cerebral myelin, which was quite mature from a morphological as well as from a biochemical point of view. These data reveal that the developmental changes of human myelin are much more subtle than has previously been thought.