Selection of Rattus norvegicus cumulus-oocyte complex for vitrification by brilliant cresyl blue.

The influence of the method of evaluating developmentally competent oocytes on their viability after cryopreservation still needs to be better understood. The objective of this study was to determine the cleavage and embryo developmental rates after parthenogenetic activation of cumulus-oocyte complexes (COCs) selected by different concentrations of brilliant cresyl blue (BCB) and cryopreservation. In the first experiment, COCs were separated into groups and incubated for 1 h in medium containing BCB (13 µM, 16 µM, or 20 µM). The control group was not exposed to BCB staining. In the second experiment, COCs were divided into four groups: 13 µM BCB(+), 13 µM BCB(-), fresh control (selected by morphologic observation and immediately in vitro matured) and vitrified control (selected by morphologic evaluation, vitrified, and in vitro matured). In the first experiment, the 13 µM BCB group displayed greater development rates at the morula stage (65.45%, 36/55) when compared with the other groups. In the second experiment, cleavage (47.05%, 72/153) and morula development (33.55%, 51/153) of the control group of fresh COCs were increased compared with the other groups. However, when comparing morula rates between vitrified COC control and BCB(+) groups, the BCB(+) group had better results (19.23%, 5/26 and 64.7%, 11/17, respectively). Our best result in rat COC selection by BCB staining was obtained using a concentration of 13 µM. This selection could be a valuable tool to improve vitrification outcomes, as observed by the BCB(+) group that demonstrated better results compared with the vitrified COC control.

Effects of environmental enrichment on reproductive performance and quantity and morphology of cumulus-oocyte complexes obtained from Rattus norvegicus.

Several researchers have observed that environmental enrichment (EE) can be effective in reducing stressful conditions and abnormal behavior and may provide better reproductive performance in rodents. In this context, this study aimed to evaluate the reproductive performance of Wistar rats reared in three different housing conditions. Animals were separated into breeding pairs, one pair per cage and pairs randomly assigned to three experimental groups (ten couples per group): control group were provided cages without any environmental enrichment; PVC group with PVC pipe; and cardboard roll group with a commercially available cardboard tube. To compare the reproductive performance of the three groups, the following were evaluated: number of pups/litter; number of litters; parturition interval; occurrence of cannibalism; weight gain of offspring; as well as the quantity and quality of cumulus-oocyte complexes (COCs) obtained after superovulation of the females born from the first, second and last pregnancy in all groups. Moreover, the plasma level of corticosterone in breeding animals was measured. A total of 60 male rats randomly selected from the first- and last-born litters (20 males from each group) were first tested in an elevated plus-maze (EPM) and on the following day, were tested in an open field test (OFT). Significant differences were found in the number and morphological classification of COCs. In the control group, the number of oocytes in grade 4 (unusual shapes and very heterogeneous ooplasm, presenting no layers of surrounding cumulus cells [13]) presented statistically higher rates (225/2535, 8.9%) compared to the other groups, as well as the number of competent oocytes was higher in the enriched groups (p = 0.001). Moreover, we find that the males of cardboard roll group differed significantly in weight gain compared to PVC group (p = 0.008). In addition to this, we did not detect occurrence of cannibalism in this group. Our findings suggest that environmental enrichment provides improvements in reproductive performance of Wistar rats.