Fourth World Conference on Early Pregnancy CONTINUUM BETWEEN IMPLANTATION AND PERINATAL EVENTS

"Syncytial Units": Individual Elements Forming The Syncytium Of The Early Human Placenta

Pirino A., Tedde Piras A., Fenu G., Bandiera P., Montella A

Department of Biomedical Sciences, Division of Human Anatomy, University of Sassari, Italy

Presentation

The trophoblast consists of two layers: the syncytiotrophoblast and the cytotrophoblast. It's well known that deep intrasyncytial clefts can be seen especially during the first period of pregnancy; such clefts arise from the fusion of Langhans cells to form the syncytium. We make the hypothesis that the syncytiotophoblastic layer is constituted, at least in the early stages of gestation, by individual syncytial elements, connected to one another by mechanical junctions, that merge as pregnancy advances.

Normal human placentas of the first trimester of pregnancy, derived from voluntary abortions, have been utilized. Clusters of villi have been submitted to trypsinization; then, the cellular elements have been collected by centrifugation and separation in Percoll gradients. The syncytial elements obtained have been attached to slides by cytocentrifugation, stained with toluidine blue, observed at the light microscope and submitted to image analysis. Some elements have been treated for the observation at the Transmission Electron Microscope and Scanning Electron Microscope.

The isolated syncytial units are multinucleated and show morphological characteristics comparable to the typical syncytiotrophoblastic structure. Single units are different from one another, with particular regard to the characteristics of the nuclei and their number. The evaluation of the number of nuclei contained in different syncytial units shows that nuclei are less numerous at the beginning of the second month of gestation and increase in number towards the end of the third in a statistic significant way; these data are in accordance with the continuous processes of fusion of Langhans cells that occur during the pregnancy to give rise to the syncytium.

In conclusion, the present study could confirm that in the early stages of gestation the syncytial layer is constituted by single, joining syncytial units that operate in close functional connection with the underlying Langhans cells.

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