Histology, histochemistry and morphometry of the ovary of the adult plains viscacha (Lagostomus maximus) in different reproductive stages

Abstract

Flamini, M.A., Barbeito, C.G., Gimeno, E.J. and Portiansky, E.L. 2009. Histology, histochemistry and morphometry of the ovary of the adult plains viscacha (Lagostomus maximus) in different reproductive stages. -Acta Zoologica (Stockholm) 90: 390-400Lagostomus maximus is a South American Hystricognathi rodent whose reproductive behaviour shows characteristics unusual for mammals, such as polyovulation (200-800 oocytes) and a high rate of embryo mortality. Thirty-six mature females captured in the province of Buenos Aires showed different physiological reproductive stages. Most of them presented a postpartum oestrus in August-September. This characteristic is different from that reported in other geographical areas. The stages considered were: anoestrus, follicular phase, early pregnancy and late pregnancy. The ovaries were light-pink and smooth and presented a tortuous cord-like aspect. Many primordial follicles were found in all the females studied. Follicles in different states of maturation and primary and accessory corpora lutea were observed in the cortex. These structures were smaller than those present in other related species. Follicles did not project into the surface of the organ. Calcified follicles of diverse size were found in all the ovaries. Atretic follicles were found in all the stages analysed. Interstitial tissue surrounding the follicles and the corpora lutea was also observed. The number and proportion of different cortical structures varied in the physiological stages analysed. The ovaries of the viscacha have differential characteristics in comparison to other Hystricognathi, some of them related to polyovulation.

Quantification of healthy and atretic germ cells and follicles in the developing and post-natal ovary of the South American plains vizcacha, Lagostomus maximus: evidence of continuous rise of the germinal reserve

“…Females exhibit the highest rate of ovulation recorded for a mammal, releasing up to 800 oocytes at each oestrus cycle (Weir 1971a). Massive polyovulation has been explained to occur as a consequence of the peculiar anatomy of the ovary characterised by a highly convoluted cortex that goes deeply into the medulla, substantially increasing the surface area for ovulation (Weir 1971b, Mossman & Duke 1973, Flamini et al 2009. In addition to the increased ovulation area, we observed sustained expression of apoptosis-inhibiting BCL2 gene and low expression of apoptosis-inducing BAX gene, which may be responsible for suppressing apoptosisdependent follicular atresia in the ovary of the adult female (Jensen et al 2006).…”

A morphological, morphometric and histochemical study of the oviduct in pregnant and non‐pregnant females of the plains viscacha (Lagostomus maximus)

“…As the viscacha naturally polyovulates 200 to 800 oocytes, only 10 of them are implanted (Weir , ; Flamini et al . ).…”

“…The reproductive cycle of the viscacha varies during the year depending on the geographical region where animals are living (Flamini et al . ). On the other hand, there have been several studies related to ovarian morphology and physiology showing that this organ is specifically adapted to polyovulation (Jensen et al .…”

Estimation, morphometry and ultrastructure of ovarian preantral follicle population in agouti (Dasyprocta leporina)

“…In mammalian species the majority of ovarian follicles usually contain only one oocyte, but the presence of follicles containing more than one oocyte has been described in many species, including some rodents as the plains viscacha (Flamini et al 2009), and the chinchilla (Sánchez--Toranzo et al 2014). These follicles may form during the earliest stages of follicle differentiation, due to an imbalance between somatic and germinal cells, which induces an incomplete germ cell cyst breakdown.…”