In vitro hormonal regulation of astrocyte proliferation.

Previously, we showed that purified myelin basic protein (MBP) induces a two-fold increase in the proliferation rate of astrocytes in culture. This observation allowed us to hipothesize that MBP-induced astroglial proliferation might be one of the causes of astrogliosis and astroglial scar formation in case of in vivo myelin breakdown. Also, we observed that dehydroepiandrosterone (DHEA) and its sulfated derivative (DHEA-S) reduce the amount of 3H-Thymidine incorporated by cultured astrocytes. In the present study, we investigated by a combined 3H-Thymidine autoradiography/immunocytochemistry technique whether the mitogenic effect that MBP exerts upon astrocytes in vitro can be prevented by DHEA and DHEA-S. Results showed that a treatment of the cells with MBP only induces approximately a two-fold increase in the number of silver grains overlaying the nuclei of astrocytes. In cultures treated with both MBP and DHEA there was a 2.5-3 fold reduction in the number of silver grains, while DHEA-S provoked a 3-4 fold reduction. These results allow us to speculate that DHEA and DHEA-S could modulate the astrogliosis that usually accompanies myelin breakdown.