Abstract
Progress in the development of rat models of human periventricular white matter injury (WMI) has been hampered by uncertainty about the developmental window in different rodent strains that coincides with cerebral white matter development in human premature infants. To define strain-specific differences in rat cerebral white matter maturation, we analyzed oligodendrocyte (OL) lineage maturation between postnatal days (P)2 and P14 in three widely studied strains of rat: Sprague-Dawley, Long-Evans and Wistar (W). We previously reported that late OL progenitors (preOL) are the major vulnerable cell type in human periventricular WMI. Strain-specific differences in preOL maturation were found at P2, such that the W rat had the highest percentage and density of preOL relative to the other strains. Overall, at P2, the state of OL maturation was similar to preterm human cerebral white matter. However, by P5, all three strains displayed a similar magnitude and extent of OL maturation that persisted with progressive myelination between P7 and P14. PreOL were the predominant OL lineage stage present in the cerebral cortex through P14, and thus OL lineage maturation occurred latter than in white matter. The hippocampus also displayed a later onset of preOL maturation in all three strains, such that OL lineage maturation and early myelination was not observed to occur until about P14. This timing of preOL maturation in rat cortical gray matter coincided with a similar timing in human cerebral cortex, where preOL also predominated until at least 8 months after full-term birth. These studies support that strain-specific differences in OL lineage immaturity were present in the early perinatal period at about P2, and they define a narrow window of preterm equivalence with human that diminishes by P5. Later developmental onset of preOL maturation in both cerebral cortex and hippocampus coincides with an extended window of potential vulnerability of the OL lineage to hypoxia-ischemia in these gray matter regions.