Early sperm-egg interaction after sperm microinjection.

The early events of sperm-egg interaction occurring 1-3 h after multiple sperm injection into the perivitelline space (PVS) and after direct injection into the ooplasm of human oocytes are reported. The sperm acrosome reaction occurred in the PVS but was not detected within the ooplasm. Sperm in the PVS were incorporated into the ooplasm in the usual manner described in vitro, after completion of the acrosome reaction, and a block to polyspermy was evident at the oolemma. However, sperm incorporation into the ooplasm was not clearly defined and requires further investigation. Sperm were also incorporated into oolemma-bound vacuoles within the ooplasm and breaches in the ooplasm were seen after intracytoplasmic injection. Both normal and abnormal sperm were found in the PVS and ooplasm, even though sperm from donors with normal semen parameters were used. The effect of freezing in liquid nitrogen on demembranation of sperm for microinjection is also reported.