Establishment of superovulation procedure in Japanese field vole, Microtus montebelli

Japanese field vole (Microtus montebelli) is a wild-derived rodent and have unique characteristic. Thus, these species have been expected as model animal. This study was performed to develop novel superovulation procedure for Japanese field vole. First, when 30 IU pregnant mare's serum gonadotropin (PMSG) and 30 IU human chorionic gonadotropin (hCG) were administrated 48 hours apart, females showed higher response to hCG compared with three concentrations of PMSG. Second, to effectively induce ovulation on females after vaginal opening, they were mated with vasectomized male instead of hCG administration. Average number of ovulated oocytes using PMSG mating (13.9 ± 1.9 oocytes) was higher than PMSG–hCG (control; 6.9 ± 2.3 oocytes) or PMSG–hCG mating (6.8 ± 0.8 oocytes). Finally, we attempted superovulation using GnRH agonist (GnRHa). With this treatment, we speculated that GnRHa might induce endogenous luteinizing hormone releasing to cause ovulation. Such superovulation was performed with 30 IU PMSG and different concentration of 20% polyvinylpyrrolidone–GnRHa (15, 30, 45, and 60 μg/kg). As results, average number of ovulated oocytes was highest with 30 μg/kg GnRHa (14.5 ± 4.1 oocytes). The numbers of ovulated oocytes of other concentrations were 5.0 ± 1.4 (15 μg/kg), 12.8 ± 2.7 (45 μg/kg), and 8.8 ± 3.7 oocytes (60 μg/kg). Nuclear status of most collected oocytes was the second meiotic division (range, 94.3%–100%). These superovulation procedures will be useful for development of in vitro culture systems and assisted reproductive technologies for not only Japanese field vole but also other voles.