Callosal oligodendrocyte number in postpartum Sprague-Dawley rats.

Prolactin (PRL), an anterior pituitary hormone with neurogenic properties associated with pregnancy, has been implicated in oligodendrocyte proliferation during gestation, contributing to increased myelination in the maternal brain. However, PRL is elevated during lactation as well, suggesting that the postpartum (PP) period may contribute to additional gliogenesis in lactating females. In the present study, we assessed oligodendrocyte number in the corpus callosum (CC) of female Sprague-Dawley rats near the end of gestation, and at two weeks postpartum in both lactating and non-lactating dams, and in virgins. Though pregnant females did not differ significantly from any other group, lactating females had significantly more oligodendrocytes in the CC than virgins (p=.01), and in medial regions of the CC than non-lactating dams (p<.02). Oligodendrocyte number in the CC of pregnant and PP females correlated positively with the number of pups in their litter (r(2)=.68, p<.005). These results suggest that the gestational period contributes to oligodendrocyte proliferation or survival, likely mediated by an endocrine hormone whose concentration varies with the size of the litter. The PP period also contributes to increases in CC oligodendrocyte number, though it is unclear whether endocrine influences and/or pup-interaction underlie the differences in myelination between lactating and non-lactating groups. Further investigation is required in order to confirm whether the effects observed are mediated by members of the PRL-family, experience, and/or other gestational/PP endocrine hormones.