Placentation in Lagostomus maximus maximus “plains viscacha” (Rodentia, Chinchillidae)

FLAMINI MA; PORTIANSKY EL; FAVARON PO; MARTINS DS; AMBRÓSIO CE; MESS A; MIGLINO MA; BARBEITO CG.

Santiago de Chile. Chile

Simposio; Meeting 2010 International Federation of Placenta Associations; 2010

Plains viscacha is a species with an ample distribution in Argentine. The gestational period is 145 -166 days, with two offspring. As member of the suborder Hystricognathi, showing a high potential as experimental model. However, only physiological data related to placentation are available so far, whereas the structural and developmental characteristics are unknown. We herein provide details based on 6 placentae of free-living animals and including stages from early pregnancy to term. Samples were obtained from Estación de Cría de Animales Silvestres, Buenos Aires, the necropsy was performed at Faculty of Veterinary Sciences, La Plata University, fixed in 4 % paraformaldehyde. The material was processed for light microscopy in Faculty of Veterinary Medicine and Animal Science, University of Sao Paulo, sectioned (5µm) and stained with haematoxylin and eosin. Macroscopically the placenta had a discoidal shape, attacked to the uterus by a peduncle, similar to other South American hystricognath rodents. The chorioallantoic placenta showed a typical lobulated structure with central maternal vessels and labyrinth, surrounded by the trophospongium. The labyrinth was dually vascularized from maternal and fetal capillaries, with trophoblast in between. The distinct subplacenta was richly vascularized, organized in lamellae situated on fetal mesenchyme and associated with layers of syncytial and cellular trophoblast. It was attached to decidua which possessed giant cells with evident chromatin. The parietal and visceral yolk sac were present. The inverted visceral yolk sac is villous with abundant blood islands. In conclusion the viscacha placenta is similar to other rodents from Suborder Hystricomorpha already studied. Once again, the current survey indicated that major qualitative aspects of placentation were independent of scale dimensions, even in larger species such as the viscacha or capybara. The current findings support the value of the guinea pig as a most promising animal model for human pregnancies, even being a small animal.