title: Chorioallantoic and yolk sac placentation in the plains viscacha (Lagostomus maximus) - a caviomorph rodent with natural polyovulation.
abstract: OBJECTIVE
  Reproduction in the plains viscacha is characterized by the polyovulation of hundreds of oocytes, the loss of implantation and the development of 1-3 offspring. Our goal was to determine whether placental development was affected by these specializations.
  
  
  METHODS
  Thirteen placentas from early pregnancy to near-term pregnancy were analyzed using histological, immunohistochemical and transmission electron microscopy.
  
  
  RESULTS
  An inverted, villous yolk sac was present. Placentas were formed by the trophospongium, labyrinth and subplacenta. A lobulated structure with a hemomonochorial barrier was established early in pregnancy. Proliferating trophoblast that was clustered at the outer border and inside the labyrinth was responsible for placental growth. Trophoblast invasion resulted from the cellular trophoblast and syncytial streamers derived from the subplacenta. Different from other caviomorphs, numerous giant cells were observed.
  
  
  CONCLUSIONS
  The principle processes of placentation in caviomorphs follow an extraordinarily stable pattern that is independent of specializations, such as polyovulation.
authors: School of Veterinary Science, National University of La Plata, Argentina.
authors: M A
authors: MA
authors: Flamini
authors: E L
authors: EL
authors: Portiansky
authors: P O
authors: PO
authors: Favaron
authors: D S
authors: DS
authors: Martins
authors: C E
authors: CE
authors: Ambrósio
authors: A M
authors: AM
authors: Mess
authors: M A
authors: MA
authors: Miglino
authors: C G
authors: CG
authors: Barbeito
mesh_terms: D000818:Animals; D005260:Female; D010060:Ovulation / Q000502:physiology*; D010920:Placenta / Q000033:anatomy & histology / Q000166:cytology; D010929:Placentation; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000502:physiology*; D012377:Rodentia / Q000502:physiology*; D014327:Trophoblasts / Q000166:cytology; D015017:Yolk Sac / Q000254:growth & development