Estrogen and apoptosis in the developing sexually dimorphic preoptic area in female rats

Effect of estrogen on apoptotic cell death was studied in the two sexually dimorphic neuronal groups in the developing rat preoptic area (POA): the anteroventral periventricular nucleus of the POA (AVPvN-POA); and the sexually dimorphic nucleus of the POA (SDN-POA). A specific labelling of nuclear fragmentation was performed by terminal deoxynucleotydyl transferase(TdT)-mediated dUTP-biotin nick end-labeling method (TUNEL method) to demonstrate apoptosis. In the AVPvN-POA whose size is larger in females than in males, the number of TUNEL-positive cells was not significantly different between day 5 control and female pups sacrificed 10 h after 25 micrograms estradiol benzoate (EB) injection. However, TUNEL-positive cells showed a significant increase in the female pups sacrificed 24 h after EB injection, compared to that shown in the control female pups. In the SDN-POA whose size is larger in males than in females, EB injection significantly decreased TUNEL-positive cells in the female pups sacrificed 24 h after EB injection, compared to that in controls. These results suggest that estrogen regulates the neuronal number by facilitating apoptotic cell death in the developing AVPvN-POA or by inhibiting it in the developing SDN-POA.