[Freezing effects on the in vitro development of mice preantral follicles]. / Influence du type de congélation sur les courbes de croissance in vitro de follicules ovariens murins.

OBJECTIVES: Comparison of in vitro development, survival and oocyte maturation rates of mice preantral follicles frozen by various methods. MATERIALS AND METHODS: Cryopreservation of the germinal cells using the slow freezing method for entire ovary (Ova Cong) or isolated preantral follicles (Iso Cong) and vitrification in a closed system of isolated preantral follicles (Iso Vitr). Non-freezing follicles were considered as the control group. The four groups were simultaneous cultured for 12 days in a microdrop system. At each day of the culture, mean diameter was measured and at the end of the culture, follicular survival and mature oocyte rates were compared. RESULTS: Iso Cong and Ova Cong follicles achieved a smaller diameter (423.0 ± 47.1 µm et 450.3 ± 15.7 µm, respectively) than control group (680.7 ± 12.3 µm) at the 12th day of culture. At the end of the culture 6.21 % of Iso Cong follicles, 53.41 % of Ova Cong follicles and 83,77 % of Control follicles were alive. Mature oocyte rates were similar for the cryopreserved groups, 44.4 % for Iso Cong group and 44.7 % for Ova Cong group, but smaller than the Control group with 90 % of mature oocytes. Only 1/171 of the Iso Vitr follicles survived to the culture. DISCUSSION AND CONCLUSIONS: This study shows that mice's ovarian follicles can grow in vitro after cryopreservation but their diameter, survival and oocytes maturation rates are smaller than in the control group.