Use of a variable electrical pulsing sequence in rabbit oocyte activation.

Variability in oocyte activation sensitivity to electrical stimuli was shown in two types of oocytes (i.e., oocytes with a whole first polar body: w-PB 1 and those with a fragmented PB 1: f-PB 1), of a similar post-ovulatory age. In order to initiate the normal activation display (i.e., extrusion of the second polar body), the w-PB 1 oocytes required, on average, 3.6 +/- 0.2 pulses and the f-PB 1 oocytes 2.9 +/- 0.1 pulses (p = 0.18). From both experimental series carried out in this work, the average haploid activation rates were 68% and 70% for w-PB1 and f-PB1 oocytes, respectively. Oocyte type did not affect the haploid embryo developmental ability observed at 24 h of culture (8-cell stage: 33-35% in Series 1 and 23-26% in Series 2), nor at 32 h of culture (16-cell stage: 77-93% and morula stage: 34-41%; Series 2). Therefore, in further experiments, the f-PB 1 oocytes may also be used as potential forerunners of haploid embryos, almost up to the morula stage.