Development of rat oocytes following intracytoplasmic injection of sperm heads isolated from testicular and epididymal spermatozoa

The possibility of obtaining normal development of rat oocytes following intracytoplasmic injection of rat sperm heads, obtained by sonicating spermatozoa from testes and epididymides, was evaluated. Irrespective of the source of spermatozoa, sperm heads were successfully injected into approximately 45% of oocytes used; after 9-12h of culture, approximately 55% of injected oocytes still had normal morphology. Of the oocytes injected with testicular sperm heads 45% were activated, with a female pronucleus and a second polar body, but significantly more oocytes (approximately 68%) injected with caput and cauda epididymal sperm heads were activated. Male pronuclear formation was observed in 67-84% of the activated oocytes, with no difference in the proportions among the different sources of sperm heads. When zygotes showing two pronuclei and a second polar body at 10h after injection were cultured in conditions that support development of 1-cell embryos produced in vivo, no embryos derived from testicular sperm heads developed to blastocysts after 120 h of culture. Development of embryos derived from cauda sperm heads was significantly higher at all points of assessment, while embryos from caput sperm showed an intermediate degree of development, compared with embryos from testicular spermatozoa. However, similar proportions (2-4%) of 1-cell embryos derived from all three groups of sperm heads developed into normal offspring after transfer to foster mothers; of the limited number of offspring tested, all were fertile. These results demonstrate that sperm heads from all sources tested are similar in their ability to contribute to full development of normal, fertile offspring.