High doses of medroxyprogesterone as the cause of disappearance of adherence of the zona pellucida to an oocyte

The zona pellucida (ZP) is an external glycoprotein membrane of oocytes of mammals and embryos in the early stage of their development. ZP first appears in growing ovarian follicles as an extracellular substance between the oocyte and granular cells. The zona pellucid markedly affects the development and maturation of the oocyte. The morphology of the ZP-oocyte complex allows a more precise determination of the oocyte maturity. According to numerous experimental studies, ZP is essential for preimplantation embryonic development of humans and other mammals. It prevents dispersion of blastomeres and enhances their mutual interactions. ZP is a dynamic structure responsible for the provision of nutrients to early forms of oocytes in mammals. The aim of the present study was untrastructural evaluation of the ZP-oocyte contact during inhibited ovulation. Female white rats (Wistar strain) received a suspension of medroxyprogesterone acetate (MPA) in incremental intramuscular bolus doses of 3.7 mg (therapeutic dose), 7.4 mg and 11.1 mg. The animals were decapitated 5 days after the administration of MPA. Ovarian sections were evaluated under a transmission electron microscope (TEM) Zeiss EM 900. Morphometric analysis of ZP was conducted using the cell imaging system by Olympus. In females exposed to therapeutic doses of MPA, ZP showed the structure of granular-fibrous reticulum of a medium electron density with single cytoplasmic processes originating from the surrounding structures. The oocyte cell membrane generated single, delicate processes directed toward ZP. Microvilli of the oocyte were short and thin. In the group receiving 7.4 mg of MPA, ZP had the structure of a delicate, loose granular-fibrous reticulum, and the oocyte cell membrane generated single microvilli directed toward ZP. In both those groups, the close ZP-oocyte contact was observed. Otherwise, in the group exposed to the highest MPA doses (11.1 mg), thicker and more numerous oocyte microvilli were found, which did not penetrate ZP matrix. They were dense, irregularly separated contour, forming a barrier between ZP and oocyte. The present findings are likely to suggest that MPA has inhibiting effects on the synthesis of binding proteins and causes the loss of the oocyte contact with ZP

Localised auxin peaks in concentration-based transport models for plants

We study the existence and bifurcation structure of stationary localised auxin spots in concentration-based auxin-transport models posed on one- and two-dimensional networks of plant cells. In regular domains with small active transport coefficient and no diffusion, the geometry of the cellular array encodes the peaks' height and location: asymptotic calculations show that peaks arise where cells have fewer neighbours, that is, at the boundary of the domain. We perform numerical bifurcation analysis for a concrete model available in literature and provide numerical evidence that the mechanism above remains valid in the presence of diffusion in both regular and irregular arrays. Using the active transport coefficient as bifurcation parameter, we find snaking branches of localised solutions, with peaks emerging from the boundary towards the interior of the domain. In one-dimensional regular arrays we observe oscillatory instabilities along the branch. In two-dimensional irregular arrays the snaking is slanted, hence stable localised solutions with peaks exist in a wide region of parameter space: the competition between active transport and production rate determines whether peaks remain localised or cover the entire domain