The interhaemal barrier in the chorioallantoic placenta of the greater mustache bat, Pteronotus parnellii, with observations on amplification of its intrasyncytial lamina

Abstract

Chorioallantoic placentae were obtained from a reproductively synchronized wild population of greater mustache bats for ultrastructural and immunocytochemical examination. The single discoidal placenta was always located in a lateral to mesometrial position on the right side of the uterus, which in the non-pregnant state is partially bicornuate. The placenta was labyrinthine and haemodichorial in advanced pregnancy. The interhaemal barrier included syncytiotrophoblast that lined the maternal vascular spaces and an underlying, continuous layer of cytotrophoblast. The barrier also contained a discontinuous extracellular layer, the intrasyncytial lamina, that was usually completely surrounded by syncytiotrophoblast. Two lines of evidence suggest that the intrasyncytial lamina may serve, in part, to strengthen the interhaemal barrier: (1) the lamina became significantly thicker as the maternal vascular channels became larger; and (2) the syncytiotrophoblast in the walls of the smallest vascular tubules expressed only very limited amounts of cytokeratins, normally a major component of the cytoskeleton of cells of epithelial origin, while the cytokeratin-rich cytotrophoblast was often highly attenuated. It was not uncommon to see gaps between the ectoplasmic processes of syncytiotrophoblast which exposed portions of the intrasyncytial lamina to the maternal vascular space. As platelet adhesion was never observed in such areas, the intrasyncytial lamina may be augmented in part by material that is non-thrombogenic.