The overlap between the fetomaternal blood systems resulted as intimate, suggesting some exchange processes. We investigated 16 pregnant females of 14 to 55 days of gestation by means of histology, morphometrics, immunohistochemistry and electron microscopy. Since previous results showed differences between the guinea pig and its close relative Galea spixii, we aimed to study subplacental development with more detail. The latter is associated with a specialized area, the subplacenta. In particular, processes of trophoblast invasion are similar. Related rodents became on focus for such purposes. It represents an area of folded layers of cellular and syncytial trophoblast, formed at the central excavation in association to the maternal blood system early in gestation, but that is supplied by fetal vessels only in later phases (Fig.1).Īnimal models are essential to understand healthy human placentation. In particular, trophoblast invasion in caviomorphs is associated with a specialized area within the placental disk, the so-called subplacenta (Kaufmann 2004, Rodrigues et al. 2012a, 2012b) revealing a quite stable pattern of evolution that is largely independent from size diameters or reproductive specializations (Kanashiro et al. 1961a, 1961b, Kaufmann & Davidoff 1977, Wolfer & Kaufmann 1980, Miglino et al. ![]() In the last decade placentation was investigated in several caviomorph species (Davies et al. Our findings are consistent with this interpretation, but suggest that hormone secretion is directed towards the fetal circulation rather than the maternal tissues. The functions that have been attributed to the subplacenta include hormone production. Within it the vessels pursue a tortuous course with sinusoidal dilatations and constrictions. The subplacenta is supplied entirely from the fetal circulation. This is probably the amylase-resistant PAS-positive material identified by histochemistry. The syncytial cytoplasm contains electron-dense granules. ![]() Microvilli project into these lacunae from the plasma membrane of the syncytiotrophoblast. The syncytiotrophoblast surrounds an extensive system of lacunae. The basal membrane of these cells is often close to fetal blood vessels. There are prominent intercellular spaces between the cytotrophoblast cells. Clusters of multinuclear giant cells occur in the transition zone between the subplacenta and decidua. Beneath this is found syncytiotrophoblast. In the subplacenta, lamellae of connective tissue support a layer of mononuclear cytotrophoblast cells. In addition, to study the microvasculature of the subplacenta, vessel casts were inspected by scanning electron microscopy. Placentae were collected from early in midgestation to near term of pregnancy and examined by standard histological techniques, immunohistochemistry and transmission electron microscopy. We here describe the subplacenta of the red-rumped agouti and examine the possible functional correlates of this structure. Beneath them, however, is a structure unique to hystricognath rodents called the subplacenta. These correspond to the labyrinthine and spongy zones of other rodent placentae. Hystricognath rodents have a lobed placenta, comprising labyrinthine exchange areas and interlobular trophoblast.
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