Effects of post-treatment with 6-dimethylaminopurine (6-DMAP) on ethanol activation of mouse oocytes at different ages

To study the effect of post-treatment with 6-Dimethylaminopurine (6-DMAP) on oocyte activation and development, mouse oocytes collected at different times post human chorion gonadotropin (hCG) injection were incubated in 6-DMAP-containing Chatot-Ziomek-Bavister (CZB) medium for different periods after ethanol exposure, and activation and development were observed. When oocytes were cultured in 6-DMAP without prior ethanol exposure, the highest activation rate was only 40%. Incubation in 6-DMAP for 6 h following ethanol exposure significantly (P < 0.05) increased the activation rate in oocytes recovered 15 and 18 h post hCG, but this effect was not significant in the 21 h oocytes. When oocytes were incubated in 6-DMAP for 1 h at different time points after ethanol, a 6-DMAP susceptible temporal window was found to be located from the second to the fifth h in the 18 h oocytes and from the fourth to the fifth h in the 15 h oocytes, and within the window, the duration of 6-DMAP incubation can be reduced to 0.5 h with more than 80% activation. With the 13 h oocytes, however, 6-DMAP-incubation can only be shortened to 3 h and no specific temporal window was identified. Oocytes that were incubated in 6-DMAP for 1 or 2 h after ethanol exposure developed to morula/blastocyst stages at significantly (P < 0.05) higher rates than those incubated in 6-DMAP for 6 h. Our results suggested that (i) long duration of 6-DMAP incubation impaired the development of mouse parthenogenotes; (ii) the effect of 6-DMAP alone was limited without prior ethanol exposure; (iii) the egg age affected both the timing of 6-DMAP susceptibility and the duration of exposure required to obtain a maximal activating effect; (iv) the most effective activating protocols varied for oocytes of different ages.