The Time of Cortical Granule Breakdown and Sperm Penetration in Mouse and Hamster Eggs Inseminated in vitro

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Abstract
The time of sperm attachment and cortical granule breakdown in intact and zona-free mouse eggs and zona-free hamster eggs at various times after insemination with capacitated sperm was examined by means of a vital staining technique. Three to 68% intact mouse eggs had sperm passing through the zona pellucida and attached to their vitellus 5–15 mm after insemination and 4–78% eggs had no or very few cortical granules 15–30 mm after insemination. The attach ment of sperm to the vitellus in the zona-free eggs was immediate, but the breakdown of cortical granules was observed in 2–15% of the mouse eggs and 65–85% of the hamster eggs within 5–15 mm after insemination. When zona-free hamster eggs were exposed to mouse sperm, the breakdown of cortical granules was observed in 4–47% of the eggs 15–60 mm after insemination. It appears that the breakdown of cortical granules after the attachment of homologous sperm occurs sooner in the hamster eggs than in the mouse eggs, but occurs much slower in hamster eggs exposed to mouse sperm, although more mouse sperm penetrated into and attached to the hamster vitellus.

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