Selection of Rattus norvegicus oocytes for in vitro maturation by brilliant cresyl blue staining

The objective of this work was to evaluate the rate of meiosis resumption and nuclear maturation of rat (Rattus norvegicus) oocytes selected for in vitro maturation (IVM) after staining of cumulus-oocyte complexes (COCs) with blue cresyl brilliant (BCB) using different protocols: exposure for 30, 60 or 90 min at 26 mu M BCB (Experiment 1), and exposure for 60 min at 13, 20 or 26 mu M BCB (Experiment 2). In Experiment 1, the selection of oocytes exposed to BCB for 60 min was found to be the most suitable, as meiosis resumption rates in the BCB+ group (n = 35/61; 57.37%) were the closest to the observed in the control (not exposed) group (n = 70/90; 77.77%) and statistically higher than the values observed for the BCB-group (n = 3/41; 7.32%). Additionally, the more effective evaluation of diagnostic tests (sensitivity and negative predictive value 100%) was observed in COCs exposed for 60 min. In Experiment 2, the 13 mu M BCB+ group presented rates of meiosis resumption (n = 57/72; 72.22%) similar to the control group (n = 87/105; 82.86%) and higher than other concentration groups. However, this results of the analysis between BCB-oocytes was also higher in the 13 mu M BCB group (n = 28/91; 30.78%) when compared with BCB-COCs exposed to 20 mu M (n = 3/62; 4.84%) or 26 mu M (n = 3/61; 4.92%) BCB. The nuclear maturation rate in the 13 mu M BCB group was similar between BCB+ or BCB-oocytes. The 20 mu M BCB group had a lower rate of nuclear maturation of BCB-oocytes than other groups. Thus, our best results in the selection of Rattus norvegicus oocytes by staining with BCB were obtained using the concentration of 13 mu M and 20 mu M, and an incubation period of 60 min.