The villous period of placentogenesis in the baboon (Papio sp.)

Abstract

Baboon placentae were studied which ranged in age from 13 to 40 days. Implantation in the baboon is superficial and a single, discoid, villous hemochorial placenta is formed. No chorionic villi develop peripheral to the placenta and there is no decidua capsularis. Trophoblastic tissue within the placenta is of two types, cyto-and syncytiotrophoblast. The chorionic villi are short and straight at 13 days but have begun to branch by 16 days. The villi consist of a mesenchymal core surrounded by a single layer of cytotrophoblast which is in turn surrounded by a layer of syncytiotrophoblast. Cytotrophoblastic cells from the distal tips of the villi spread over the maternal surface of the placenta and form a complete cytotrophoblastic shell against the uterine stroma. Maternal blood enters and leaves the intervillous space through clefts in the cytotrophoblastic shell which connect with arteries and expanded venules within the endometrium. A limited decidualization of the uterine stroma takes place.Early stages of baboon placentogenesis have been described by Noback ('46) who reported on a single specimen from late in the first month of gestation, by Gilbert and The purpose of this paper is to describe the structural changes which occur in the baboon placenta from the appearance of the chorionic villi until the definitive embryonic placenta is established. MATERIALS AND METHODSA total of 66 placentae ranging in insemination age from 13 to 40 days were employed in the present study. The distribution of the specimens was as follows: 13-15 days, 5 specimens; 16-18 days, 7 specimens; 19-21 days, 8 specimens; 22-25 days, 16 specimens; 26-30 days, 17 specimens; 31-40 days, 13 specimens. The placentae were obtained by cesarean section according to the method of Claborn et al. ('67). The insemination age was based on single matings of 2 to 12 hours duration with the day of mating considered day zero, or in cases where mating extended over more than a one-day period the third day preceding perineal deturgescence was designated day zero (Hendrickx and Kraemer, '68).The placentae were fixed in 10% buffered formalin, Bouin's fluid or FAA (5 parts formalin, 5 parts glacial acetic acid and 90 parts 80% ethyl alcohol), dehydrated, embedded in Paraplast and sectioned at 6 to 10 p. Younger specimens were sectioned serially with the embryo intact and stained with hematoxylin and eosin. Older embryos were removed and sectioned separately and serial sections were made from blocks of placental tissue. In these cases, alternate sections were stained with hematoxylin and eosin, and Mallory's triple, Masson's trichrome or Enders-Mossman-Groat placental stain. OBSERVATIONSImplantation in the baboon is superficial and central with chorionic villi formed only over the embryonic pole of the blastocyst, the original site of attachment to the uterine mucosa. This results in the formation of a single discoid or slightly ovoid placenta with a membranous, avillous paraplacental chorion and no decidua capsularis. Placentation in the baboon wil...

Trophoblast differentiation during the transition from trophoblastic plate to lacunar stage of implantation in the rhesus monkey and human

“…The transition from the trophoblastic plate stage to the lacunar stage involves the establishment of potential blood spaces and the confluence of these spaces with maternal endometrial vessels, positional changes in cytotrophoblast and svncvtial troDhoblast, and prob- and baboon (Houston, 1969;Tarara et al, 1987) and the development of lacunae directly beneath the chorionic plate tend to result in elevation of the placental discs from the level of the endometrial surface. In the human, there is some possibility that the maternal vessels are surrounded by trophoblast before being tapped (Ramsey et al, 19761, which may of itself lead to a more labyrinthine condition.…”

“…In the human, these spaces are somewhat labyrinthine Rock, 1945, 1949;Ramsey et al, 1976). In the baboon, the rapid enlargement of the lacunae near the chorionic surface elevates the placenta from the level of the endometrial surface (Houston, 1969;Tarara et al, 1987). In the rhesus monkey also, the larger lacunae form near the chorionic surface, but the placenta is not as elevated as in the baboon and a secondary placenta forms on the opposite side (Wislocki and Streeter, 1938).…”

“…The origin of the lacunae themselves is more obscure. Houston (1969Houston ( , 1971 suggested that there were a few clefts in the syncytial trophoblast of the baboon prior to lacuna formation. In a study of implantation in the rhesus monkey, it was noted that there was regional differentiation of syncytial trophoblast either preceding or at the same time that maternal vessels were tapped (Enders et al, 1983).…”

Implantation and Establishment of Pregnancy in Human and Nonhuman Primates

“…In humans, the blastocyst is completely embedded within the endometrial stroma at 8 days after ovulation and the entry site is covered by fibrin, over which the endometrial epithelial cells grow and embed the blastocyst in the endometrium (Bischof and Campana 1996). In nonhuman primates such as gibbons, gorillas, and chimpanzees, implantation is also invasive, like humans, whereas in baboons and macaques, implantation is superficial (Carter and Pijnenborg 2011; Houston 1969). …”

Early Placentation in the African Green Monkey (<i>Cercopithecus aethiops</i>)

“…1938: King andMais, 1982] and baboon [Noback, 1946: Houston. 1969], Due to the absence ofa decidua capsularis.…”