Sonication per se is not as deleterious to sperm chromosomes as previouslyinferred

Although sonication is a simple way to immobilize ("kill") spermatozoa prio r to injection into oocytes, this has been thought to be destructive to spe rm chromosomes, Mouse and human spermatozoa were immobilized by sonication and kept in various media for up to 2 h, then their nuclei were individuall y injected into mouse oocytes for the analysis of chromosomes at the first cleavage metaphase, In both the mouse and human, incidence of structural ch romosome aberrations was much higher in the spermatozoa sonicated and store d in Biggers-Whitten-Whittingham medium for 2 h at 37.5 degrees C than in t hose stored for 5 min in the same medium. We concluded, therefore, that it is not sonication per se but a prolonged exposure of sperm nuclei to extrac ellular milieu that is detrimental to sperm chromosomes. The incidence of s tructural chromosome aberrations of mouse and human spermatozoa was signifi cantly reduced when the spermatozoa were sonicated and stored in K+-rich nu cleus isolation medium containing EDTA, This suggests that sperm chromosome degradation following sperm immobilization by sonication is partly due to detrimental effects of a Na+-rich medium and of DNase on sperm chromatin. I deally, it should be possible to prepare artificial media that maintain the integrity of sperm chromosomes for many hours after immobilization.