Abstract
Rat oocytes are known to be activated in vitro spontaneously. In the present study, we examined the effect of oocyte preincubation on the survival and development of oocytes after intracytoplasmic sperm injection (ICSI) in rats. Some presumptive oocytes produced by ICSI were transferred into the oviduct or ovarian bursa of recipient females to observe the development to term. When ICSI was performed without oocyte preincubation, the rate of oocyte survival was 90.5%, normally fertilized, 82.5%, and cleaved, 58.7%. These rates were reduced by oocyte preincubation for 3 or 5 h and the reduction could be related to the incomplete spontaneous activation of oocytes, which is known to result in no pronucleus formation and no cleavage. Both oviduct and ovarian bursa transfer allowed us to produce live offspring after ICSI (19.5 and 21.7% of transferred oocytes, respectively). Rat offspring could be produced by the ICSI protocol commonly used in mice. In rats, shortening of the period from oocyte recovery to sperm injection might be an important factor in the production of live offspring after ICSI. Intra-ovarian bursa transfer is technically easy and has been successfully applied to the production of rat offspring after various manipulations of oocytes, including ICSI.
