Early and natural embryonic death in Lagostomus maximus: Association with the uterine glands, vasculature, and musculature

Abstract

The uterus is an organ with great plasticity due to the morphological and physiological changes it experiences during the estrous cycle and pregnancy. In mammals, pregnancy requires diverse sex hormones, growth factors and cytokines, among others, for promoting uterine remodeling to favor implantation, placentation, and embryo/fetus survival and growth. The hystricognathi rodent Lagostomus maximus (plains viscacha) has a high rate of embryonic resorption. The cranial and middle implants are reabsorbed 25–35 days after intercourse while the caudal embryos continue with their development until two precocial offspring are born. So far, no uterine studies of non‐pregnant L. maximus females were performed to determine the possible existence of variations in the organ that could be related to the differential survival of the implants. We used ultrasonography, as well as morphological, morphometric, histochemical, lectinhistochemical, and immunohistochemical methods to study differences in the uterine glands (area), vasculature (area), and musculature (thickness) along the uterine horns in non‐pregnant females. Along the uterus, all these structures were in more advanced developmental condition in the caudal region as compared to more anterior positions. These regional variations could be decisive in explaining the reason why only caudal implantations come to term. In contrast, no differences in the in the luminal and glandular epithelial cells, nor in the degree of cell proliferation and apoptosis, and hormonal receptor staining were found. These parameters could be related to implantation along the uterine horns, but not to the differential survival of the implants.

Prenatal development in Lagostomus maximus (Rodentia, Chinchillidae): A unique case among eutherian mammals of physiological embryonic death

“…In addition, a greater caliber in the branches of the arteries that supply the caudal embryos with respect to those close to the ovary was documented (Giacchino et al, 2020). In these same anatomical regions, it was also shown that in non‐pregnant adult females there is a significant increase in the glandular area as compared to that established in the cranial and middle uterine regions, sites where concepti resorption occurs (Acuña et al, 2020). The reproductive success of mammals depends on the energy that females invest before and after giving birth (Curley et al, 2005).…”

“…Females were euthanized following a standard protocol (Acuña et al, 2018) to extract the entire reproductive system. Briefly, captured viscachas were intramuscularly anesthetized by administering a single dose of xylazine (Anasedan, Laboratorio Vetbrands) (8 mg/Kg of body weight) followed by ketamine (Ketanest, Laboratorio Scott Cassara) (50 mg/Kg body weight) (Acuña et al, 2020). After death, the reproductive system was removed and photographed.…”

“…The cranial and caudal segments and all the implantation sites of the right uterine horns were processed for paraffin embedding, according to the standard protocols of our laboratory; 3 μm thick slides were used (Acuña et al, 2020; Flamini et al, 2019; Flamini et al, 2020).…”

“…Only the two implantations located in the caudal segments of both uterine horns are those that will survive (Flamini et al, 2019). In this way, L. maximus constitutes an unconventional mammalian model for the study of early and physiological embryonic death (Acuña et al, 2020).…”

“…However, recently, from more exhaustive morphological studies, it was reported that there is a greater vascularization in the caudal area of the organ. These changes in the vasculature are established in prenatal life (Flamini et al, 2020) and are maintained in non‐pregnant adult females (Acuña et al, 2020). The most vascularized regions correspond to the sites where during pregnancy the concepti are located that will continue with their development (Flamini et al, 2020).…”