Abstract
BackgroundThe placenta of hystricomorph rodents, lagomorphs and some primates includes an unusual structure, termed a subplacenta, which essentially consists of trophoblastic cells located deep to the central implantation site within the area of decidualization. It has been suggested that the subplacenta is functionally important, although considerable controversy remains on the issue. In this context, our objective was to compare the architecture and structure of the subplacentas of different hystricomorph species, to investigate the possibility that it is active in hormone synthesis.MethodsIn total, the placentas of 3 capybaras (Hydrochaeris hydrochaeris), 2 pacas (Agouti paca), 5 agoutis (Dasyprocta leporina), 5 rock cavies (Kerodon rupestris) and 3 guinea pigs (Cavia porcellus) at different stages of pregnancy (early, middle and near term) were used for gross and microscopic examination. This included the preparation of latex injection casts, immunohistochemistry for steroidogenic enzymes, scanning and transmission electron microscopy. Tissue steroid concentrations were also determined.ResultsThe gross morphology and microvascular arrangement of the subplacentas were similar among the hystricomorphs studied including ultra-structural verification of cytotrophoblast and syncytiotrophoblast in all species. In guinea pigs, trophoblast cells exhibited characteristics consistent with intense metabolic and secretory activity in general. However, immuno-histochemical evidence also indicated that subplacental trophoblast expressed key steroidogenic enzymes, mainly in the chorionic villus region, consistent with tissue steroid concentrations.ConclusionsThe subplacentas within placentas of hystricomorph rodent species are structurally similar and, in guinea pigs, have potential for steroid hormone secretion from, at least the early stages of pregnancy.
Highlights
The placenta of hystricomorph rodents, lagomorphs and some primates includes an unusual structure, termed a subplacenta, which essentially consists of trophoblastic cells located deep to the central implantation site within the area of decidualization
Some species within the Hystricomorph and Lagomorph sub-orders of the Rodentia have a specialized structure within their placentas, called a subplacenta [14,15,16,17,18], that is unusual among mammals
Morphology and immuno-histochemistry The gross morphology and microvascular arrangements of the subplacenta of these hystricomorph rodents were observed during pregnancy (Fig. 1A-D)
Summary
The placenta of hystricomorph rodents, lagomorphs and some primates includes an unusual structure, termed a subplacenta, which essentially consists of trophoblastic cells located deep to the central implantation site within the area of decidualization. The success of viviparity in eutherian mammals is dependent on the establishment of a fully functional chorioallantoic placenta in order to sustain successful embryonic and fetal development In this context, placental development from trophoblast is mediated in part by interactions between maternal endometrial and extraembryonic tissues during the implantation process [1,2,3,4,5]. The structure is represented by zone of chorionic ectoderm, which is located in the central excavation of the placenta and is limited to the area of decidualization [19] The functions of this placental specialization remain unclear [1]. According to [23] none of these hypotheses has been resolved to a sufficient degree
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