Viable rat offspring derived from oocytes intracytoplasmically injected with freeze-dried sperm heads.

A 2 x 3 factorial designed experiment was conducted in order to examine whether freeze-dried rat spermatozoa can participate in full-term development following intracytoplasmic sperm injection (ICSI). A sperm suspension from cauda epididymides of Sprague-Dawley (SD) rats was prepared with or without ultrasonic treatment. The sonicated and non-sonicated sperm suspensions were processed for freeze-thawing (FT groups; 100 microl sample was cooled in liquid nitrogen vapor, stored for 1 day at--196 degrees C, and thawed in a 25 degrees C water bath) and freeze-drying (FD groups; 100 microl sample was frozen in liquid nitrogen for 20 s, lyophilized for 6 h, stored at 4 degrees C for 2 days, and rehydrated with 100 microl ultrapure water), or were subjected to immediate use for ICSI (fresh control groups). The sperm heads were microinjected into denuded SD oocytes using a piezo-driven micropipette 2-4 microm in diameter. The presumptive zygotes were transferred into oviducts of pseudopregnant Wistar female rats. Viable rat offspring were produced from all six experimental groups. Ultrasonic treatment of rat spermatozoa was effective in increasing the offspring rate (23.3% vs 6.7% in fresh control groups, 35.0% vs 7.6% in FT groups, 9.2% vs 2.5% in FD groups). The acrosomal region appeared to be intact even after ultrasonic FT and FD treatments as well as in the fresh controls, while the lateral dorsal region of the sperm membrane was more or less damaged in the sonicated, FT and FD samples. Thus, the successful participation of freeze-dried spermatozoa in full-term development was demonstrated by applying ICSI in the rat.