BEHAVIOR OF SPERMATOZOA IN HUMAN OOCYTES DISPLAYING NO OR ONE PRONUCLEUS AFTER INTRACYTOPLASMIC SPERM INJECTION

The behaviour of sperm cells after intracytoplasmic sperm injection (I CSI) was investigated by analysing 199 unfertilized and 37 one-pronucl ear (1PN) oocytes following ICSI. Eighty-two unfertilized oocytes were directly feued whereas 110 were first parthenogenetically activated b y puromycin. In contrast to the findings in unfertilized oocytes after in-vitro fertilization, most unfertilized oocytes after ICSI (n = 76) contained evidence of the presence of spermatozoa in the cytoplasm. F ew oocytes (n = 6) contained prematurely condensed sperm chromosomes ( PCC), whereas the majority contained either intact sperm heads (n = 31 ) or swollen sperm nuclei (n = 39) along,vith metaphase II chromosomes of the oocyte. Following activation by puromycin, swollen sperm nucle i and PCC were no longer observed, whereas unchanged sperm heads persi sted in 12 oocytes displaying a single pronucleus. A non-decondensed s perm nucleus along with decondensed maternal chromatin were also disco vered in 32 out of 37 oocytes displaying a single pronucleus after ICS I. The findings in unfertilized and 1PN oocytes after ICSI indicate th at successful sperm injection, even followed by oocyte activation, is not sufficient to guarantee normal fertilization. It seems that partia l sperm membrane damage prior to injection is also required to ensure normal sperm decondensation.