Morphological changes in the trophoblast, uterus and corpus luteum during delayed implantation and implantation in the western spotted skunk

Morphological interactions of trophoblast and uterus from stages of preimplantation and implantation were studied in 14 western spotted skunks. In addition, the granulosa lutein cells and plasma progesterone levels were studied. In animals several days from implantation the height of epithelial cells decreased, but began to increase in animals approaching implantation. During the preimplantation period a few leucocytes infiltrated the epithelium, but in animals just prior to implantation many leucocytes infiltrated the epithelium. However, in the implanted animals leucocyte infiltration was not observed. The increased infiltration of epithelium was possibly in response to the proximity of trophoblast or due to some antigenic material from the trophoblast. The unimplanted blastocyst had a layer of trophoblast and the embryonic disc. As implantation approached, the trophoblast formed trophoblastic knobs which apposed the luminal epithelium. Subsequently microvilli of trophoblastic and epithelial cells interdigitated. Junctional complexes were observed between many adhering microvilli and/or cell processes. The first attachment of trophoblast and epithelium occurred in the abembryonic region. Later the trophoblastic cell processes and/or individual cells penetrated the epithelium and reached the basal lamina. In addition to the penetration of the trophoblast, sometimes individual trophoblastic and epithelial cells fused. In the fused cells, remnants of junctional complexes and plasma membranes were observed. The fused cells did not penetrate the basal lamina and were not observed in the stroma. During the delay period the corpus luteum contained predominantly small granulosa cells and some large granulosa lutein cells, but only large lutein cells were observed in the implanted animals. The plasma progesterone levels fluctuated during the time of implantation and should not be regarded as a basis to predict nidation in the skunk.