The ultrastructure of the fowl spermatozoon was examined before and after direct immersion in liquid nitrogen (−196° C). Two cryopreservatives, glycerol and dimethylsulphoxide (DMSO), were added to an isotonic monosodium glutamate diluent to give a final concentration of 8% or 16%.
The changes in morphology attributed to rapid freeze—thaw were as follows: (1) extensive divergence of the cytoplasmic membrane in the majority of the spermatozoa throughout their entire length; (2) complete destruction of the cytoplasmic membrane surrounding the acrosomal region in some spermatozoa with subsequent release of the contents of the acrosomal cap into the diluted seminal plasma; (3) release of the mitochondria of the mid-piece into the surrounding media upon destruction of the cytoplasmic membrane. The axoneme complex remained intact even though the cytoplasmic membrane was completely destroyed.
No differences were noted before freezing between spermatozoa suspended in the control glutamate diluent alone and diluents containing a cryopreservative. The addition of glycerol and the highest level of DMSO did not prevent extensive damage to the membranes during rapid freezing and thawing. Reduced membrane damage indicated that the lower level of 8% DMSO partially protected some spermatozoa.