Effect of freezing on ultrastructure of chimpanzee sperms as revealed by ethanol cryofracture and scanning electron microscope.

Ultrastructural features of fresh chimpanzee spermatozoa were studied following ethanol cryofracture of sperm pellets. Fresh and freeze preserved semen samples used for artificial insemination were fixed in 2.5% glutaraldehyde in 0.1 M cacodylate buffer. The centrifuged cells in the form of a pellet were post fixed in 1% osmium tetroxide in 0.1 M cacodylate buffer. The ethanol dehydrated pellets were cryofractured, critical point dried from liquid CO2, mounted on stubs and decorated with 5-6 nm gold palladium. When compared with fresh samples the ultrastructural features of spermatozoa showed the following changes. The most conspicuous changes were noted in the acrosomal membrane region. The acrosomal membrane becomes swollen wavy and broken at several points. The plasma membrane around the neck region was thinned out with mitochondrial sheath being pulled back. The general 9 + 2 arrangement of the axoneme was unchanged. Thus critical changes in the membrane structure and mid piece morphology may account for the present failure of artificial insemination procedure using frozen sperm in this primate species.