Background: Tamoxifen treatment induced cell death in the hippocampus formation of the prenatal and
postnatal rat. The present study delineates the effect of tamoxifen on developing hippocampus in prenatal,
postnatal and full term neonate rats received certain doses of the partial antagonist tamoxifen. Methods: After
perfusion and fixation, the brains were removed and processed for light and electron microscopy. The
morphology, ultrastructure and the density of the neurons in different ages (E22, P1, P7 and P21) and in
different areas of developing hippocampus including cornu ammonis (CA1 and CA3), dentate gyrus and
subiculum were studied. Results: These findings showed that in tamoxifen-treated groups, the cell number of
pyramidal neurons of CA1 and subiculum significantly decreased comparing to control groups in E22, P1 and
P7 but not in third weeks. The mitochondria of the above mentioned groups also showed a dilated feature with
less cristae than control group and most of them were greatly enlarged and swollen into spherical shapes
rather than the normal ovoid or rod shape. Conclusion: The present study shows that prenatal exposure to
tamoxifen alters neurogenesis in developing rat hippocampus. These results demonstrated the nonneuroprotective
roles of tamoxife
