Placentation and embryo death in the plains viscacha (Lagostomus maximus).

Caviomorpha are an exceptional group among rodents due to their extended gestational period and the delivery of precocial offspring. Among them, Lagostomus maximus is characterized by its polyovulation, polyembryony, and the highest embryonic death known in mammals. Its chorioallantoic placenta is hemomonochorial, an ancestral character among rodents. It resembles more the human placenta than the murine models. As in all caviomophs, the chorioallantoic placenta is divided in a main placenta and a subplacenta. The former is organized in labyrinth lobes surrounded by trophospongium, as in most caviomorphs. The giant cells (more numerous than in other caviomorphs) near the decidua could be related to invasiveness. During placentation of L. maximus, uterine natural killer cells are found. These cells have been related to invasiveness and remodeling of blood vessels in Mus musculus and Homo sapiens, although in other caviomorphs are not frequently found. In L. maximus, the placenta develops in all conceptuses (5-6 per uterine horn). Necrosis was observed in each implantation site at day 70 post-coitum, except in that closest to the vagina in each horn. This process of embryo death followed by resorption begins at day 26-30 post-coitum. Recently, we found variations in the percentage of blood vessel and uterine gland areas that could explain the regional differences in embryo survival. The characteristics of the placenta and implantation of L. maximus are important to stablish a unique model for studying placentation as well as early embryonic death, of interest for human and veterinary medicine.

Hans Bluntschli in Berne: Researching reproduction in hedgehog tenrecs (Afrosoricida, Tenrecidae).

The Swiss anatomist Hans Bluntschli is best known as a primatologist. Yet, his focus during his later years in Berne was on reproduction in Malagasy tenrecs. This research was done with two graduate students, Robert Goetz and Fritz Strauss; all three had been obliged to leave Germany after the National Socialists came to power. Unique features of reproduction in tenrecs included nonantral follicles, intrafollicular fertilization, eversion of the corpus luteum, and polyovulation. The fertilized egg formed a blastula that developed into a blastocyst; there was no morula stage. A false placental cushion developed in the endometrium opposite the implantation site. Placentation was complex and included development of a prominent haemophagous organ. These findings are discussed in relation to current concepts of mammalian phylogeny that place tenrecs and golden moles in the same order and as close relatives to elephant shrews and the aardvark.

Classics revisited: C. J. van der Horst on pregnancy and menstruation in elephant shrews.

BACKGROUND: Menstruation occurs only in higher primates, some bats, the spiny mouse and the elephant shrew. Our knowledge of the latter species is due to work by C. J. van der Horst. FINDINGS: Changes in the uterine stroma are initially similar in fertile and infertile cycles and are confined to a small area. In pregnant animals, the presence of the conceptus causes further development to an implantation chamber. In infertile cycles an outgrowth of highly glandular stroma (a polyp) appears. With decline of the corpora lutea it is shed in a process equivalent to menstruation. Van der Horst described the further development of the placenta and a decidua pseudocapsularis in pregnant animals. In addition he built a unique collection that has thrown light on embryonic development and placentation in other South African mammals. CONCLUSIONS: The changes in endometrial stromal cells during the menstrual cycle appear similar between primates and the elephant shrew and deserve to be studied at the molecular level.