Ultrastructures of Frozen-thawed Boar Spermatozoa

Abstract

Boar spermatozoa were frozen in a plastic tube with or without Orvus ES Paste (OEP), and the ultrastructures were observed after thawing by a conventional ultrathin sectioning and by a deep-etch method. Spermatozoa frozen without OEP showed characteristic features: 1) The cell membrane covering the acrosome was not present, 2) the principal segment of the naked acrosome was dilated, and 3) the acrosomal contents seemed to be dispersed. The volume of the principal segment was increased at least several times. The inner acrosomal membrane seemed to be intact, but the outer acrosomal membrane was expanded without a break or hole. Other structures, including those in the tails, were normal. However, most spermatozoa frozen with OEP were normal in ultrastructure. During freezing and thawing, OEP seems to stabilize the outer acrosomal membrane as well as the cell membrane in the acrosome region.