Blastocyst implantation in rats: a morphological approach.

Very complex cellular events take place at the morphological and molecular levels both in the maternal and embryonic sites during blastocyst implantation. Although the morphological alterations in the gestational stages of the implantation site are well-known, mechanisms of the interaction between blastocyst and endometrial epithelium (apposition and adhesion stages) and penetration of the blastocyst into the endometrium have not yet been fully described. Therefore the present study was designed to determine these events morphologically throughout the implantational stages. To do this the endometrial tissues containing implantation sites from pregnant rats were taken 5 and 8 days after fertilization. In addition, non-pregnant rat endometrial tissues were also obtained in order to use as control. Tissues were processed for light and electron microscopy. Semi-thin and ultra-thin sections were stained using appropriate staining methods, and were evaluated under light and electron microscope. In the present study, interaction between trophoblast and luminal epithelium, penetration of the blastocyst into the endometrium, differentiation of germinal layers in the blastocyst and tissue alterations such as decidualization in the maternal site have been demonstrated morphologically. In conclusion, while blastocyst was implanted into the endometrium, distinct morphological changes occurred both in maternal and embryonic sites. The following stages of implantation were the development of germinal layers in the embryo and morphological changes in the maternal site leading to the placentation.