X-ray Sensitivity of Primary Spermatocytes of the Mouse

Summary

The radiation sensitivity of mouse primary spermatocytes to cell-killing was estimated by the number of spermatids produced; sensitivity to chromosome breakage was measured by scoring abnormal divisions at anaphase I and II. There was an inverse relation between cell-killing and chromosome breakage: pre-leptotene was the most sensitive and diakinesis-metaphase I the most resistant to induction of cell death; whereas pre-leptotene and leptotene were the most resistant and metaphase I the most sensitive to chromosome breakage. The relative sensitivities of primary spermatocyte stages to chromosome breakage are similar to those observed for meiotic cells in other organisms. Stage differences between leptotene and pachytene in sensitivity to chromosome breakage in the mouse are as large as those sometimes claimed for species differences. The need for accurate information on the duration of spermatogenesis is emphasized in order that species comparisons should not be confused with stage differences in sensitivity. Determination of the number and morphology of spermatozoa ejaculated at successive intervals after irradiation revealed no changes as spermatozoa and spermatids were utilized, a decrease in number and an increase in abnormal sperm from spermatocytes, a severe oligospermia from destruction of spermatogonia, and a return to normal number after regeneration of the testis.