Elsevier

Placenta

Volume 27, Issue 1, January 2006, Pages 87-97
Placenta

Placentation in the rock cavy, Kerodon rupestris (Wied)

https://doi.org/10.1016/j.placenta.2004.11.012Get rights and content

Rock cavies are rodents found in the semi-arid caatinga of Brazil. We studied the structure of the rock cavy placenta by light and transmission electron microscopy. The exchange area of the labyrinth was organized in lobes separated by interlobular areas. The interhaemal barrier was syncytial haemomonochorial. The syncytiotrophoblast had recesses in the basal membrane and some invaginations of the apical membrane, but transtrophoblastic channels could not be found. The interlobular regions comprised syncytiotrophoblast, enclosing maternal venous blood channels, and cytotrophoblast. There was a prominent subplacenta composed of cytotrophoblast and syncytiotrophoblast. Microvilli projected into spaces between the cytotrophoblasts and into lacunae within the syncytiotrophoblast. The yolk sac epithelium exhibited coated pits, endocytotic vesicles and larger vacuoles, consistent with a role in protein uptake from the uterine lumen. Tight junctions between these cells provided a barrier to diffusion by the intercellular route. The reproductive biology of the rock cavy differs from other members of the family, including the guinea pig, but the architecture of the placenta remains remarkably constant.

Introduction

The rock cavy, Kerodon rupestris (Wied), lives in the semi-arid caatinga of northeast Brazil. Its local name is the mocó. It belongs to the same family as the guinea pig (Caviidae), but although similar in size to the guinea pig, it differs in general appearance and way of life. Rock cavies are gregarious and crepuscular, passing the day in burrows under rocks or stones. They leave their shelters in the late afternoon or evening and run on the ground or climb trees looking for food, mainly tender leaves. They are especially partial to some species of creeper [1], [2].

The rock cavy is an extreme habitat specialist, having adapted to the near arid conditions of the caatinga [3], [4]. It is currently under threat due to destruction of this habitat as well as hunting. Elsewhere, efforts are underway to raise rock cavies under controlled conditions as a potential source of food [5]. It is therefore important to understand the reproductive biology of this species.

The placentae of hystricomorph rodents have a number of distinguishing features [6], [7], [8]. These include a varying amount of lobulation of the exchange area and the presence of a subplacenta. As in many rodents, an inverted yolk sac placenta is present until term. The present study was undertaken to describe the morphology of the rock cavy placenta at the light microscopical and ultrastructural level and to compare it with the placentae of other hystricomorph rodents [9].

Section snippets

Tissue collection

Placentae, fetal membranes and parts of the uteri were collected from 15 rock cavies bred in captivity at the Center for Breeding of Wild Animals, Mossoró. The research was authorized by the Brazilian Institute of the Environment and Renewable Natural Resources (IBAMA). The experimental protocol was approved by the Bioethics Committee of the School of Veterinary Medicine, University of Sao Paulo.

The animals were premedicated with midazolam (Dormine, Cristália, Itapira, S.P., Brazil; 1 mg/kg) and

Results

We obtained five placentae from early gestation, five from mid-gestation and seven from late gestation. There were two pairs of twins and 13 singleton pregnancies. Details of fetal and placental weight and size are given in Table 1. Maternal weight ranged from 0.7 to 1.0 kg. In late gestation, combined fetal and placental weights were 4.1% of maternal weight for singleton pregnancies and 10.9% for twin pregnancies.

Discussion

The overall plan of the rock cavy placenta resembles that of other hystricomorph rodents [6], [7], [8], [9]. It is highly lobed with a prominent subplacenta. The structure of hystricomorph placentae at the light microscopical level has been dealt with elsewhere [9], as has the vascular architecture of the placenta [10]. The present discussion focuses on the reproductive biology of the rock cavy; placental investments, which differ between species; and placental ultrastructure.

Acknowledgements

This study was supported by Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Brazil. We are grateful for the skilled assistance of Antonio Almeida dos Santos, Caubi Rocha de Macedo and the kind support of Professor Idércio Luiz Sinhorini and Dr. Tatiana Carlesso dos Santos.

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