Fig. 9.

Quantitative analysis of the timing of appearance of pre-OLs and immature OLs in human cerebral white matter between 18 and 41 weeks. Each time point represents an individual case in which the percentage of immature OLs was determined from the total OL somata that labeled with the O1 antibody. Because the O4 antibody was found to label the entire population of OL precursors at all ages examined, total OL precursors were determined from the number of cells that labeled with O4 (see Materials and Methods). Note that O1+ immature OLs are a minor population between 18 and 28 weeks. Approximately 28–30 weeks mark the onset of an expansion in the immature OL population.