title: Morphometric analysis of the placenta in the New World mouse Necromys lasiurus (Rodentia, Cricetidae): a comparison of placental development in cricetids and murids.
abstract: BACKGROUND
  Stereology is an established method to extrapolate three-dimensional quantities from two-dimensional images. It was applied to placentation in the mouse, but not yet for other rodents. Herein, we provide the first study on quantitative placental development in a sigmodontine rodent species with relatively similar gestational time. Placental structure was also compared to the mouse, in order to evaluate similarities and differences in developmental patterns at the end of gestation.
  
  
  METHODS
  Fetal and placental tissues of Necromys lasiurus were collected and weighed at 3 different stages of gestation (early, mid and late gestation) for placental stereology. The total and relative volumes of placenta and of its main layers were investigated. Volume fractions of labyrinth components were quantified by the One Stop method in 31 placentae collected from different individuals, using the Mercator software. Data generated at the end of gestation from N. lasiurus placentae were compared to those of Mus musculus domesticus obtained at the same stage.
  
  
  RESULTS
  A significant increase in the total absolute volumes of the placenta and its main layers occurred from early to mid-gestation, followed by a reduction near term, with the labyrinth layer becoming the most prominent area. Moreover, at the end of gestation, the total volume of the mouse placenta was significantly increased compared to that of N. lasiurus although the proportions of the labyrinth layer and junctional zones were similar. Analysis of the volume fractions of the components in the labyrinth indicated a significant increase in fetal vessels and sinusoidal giant cells, a decrease in labyrinthine trophoblast whereas the proportion of maternal blood space remained stable in the course of gestation. On the other hand, in the mouse, volume fractions of fetal vessels and sinusoidal giant cells decreased whereas the volume fraction of labyrinthine trophoblast increased compared to N. lasiurus placenta.
  
  
  CONCLUSIONS
  Placental development differed between N. lasiurus and M. musculus domesticus. In particular, the low placental efficiency in N. lasiurus seemed to induce morphological optimization of fetomaternal exchanges. In conclusion, despite similar structural aspects of placentation in these species, the quantitative dynamics showed important differences.
authors: Department of Surgery, School of Veterinary Medicine, University of Sao Paulo, Av. Prof, Dr. Orlando Marques de Paiva, 87, Cidade Universitária, São Paulo, SP CEP 05508-270, Brazil. phelipe.favaron@yahoo.com.br
authors: Phelipe O
authors: PO
authors: Favaron
authors: Andrea M
authors: AM
authors: Mess
authors: Moacir F
authors: MF
authors: de Oliveira
authors: Anne
authors: A
authors: Gabory
authors: Maria A
authors: MA
authors: Miglino
authors: Pascale
authors: P
authors: Chavatte-Palmer
authors: Anne
authors: A
authors: Tarrade
mesh_terms: D000818:Animals; D003411:Arvicolinae / Q000196:embryology / Q000254:growth & development; D005260:Female; D051379:Mice / Q000196:embryology* / Q000254:growth & development; D008810:Mice, Inbred C57BL; D008811:Mice, Inbred DBA; D009115:Muridae / Q000196:embryology* / Q000254:growth & development; D010920:Placenta / Q000166:cytology / Q000196:embryology*; D010929:Placentation / Q000502:physiology*; D011247:Pregnancy; D016205:Sigmodontinae / Q000196:embryology* / Q000254:growth & development; D013045:Species Specificity