The squash technique employed in the present study allowed rapid parallel detection of apoptotic cells together with accurate identification of the stage of spermatogenesis in immature rat seminiferous epithelium. The frequency of appearance of the different spermatogenic stages and the most advanced germ cell types in squashed tubular segments were comparable to earlier data from tubular crosssections reported by Clermont and Perey.
When the kinetics of the appearance of the most advanced germ cells was compared to the data published by van Haaster and de Rooij, a similar accelerated rate of progression of the spermatogenic cycle during the first 18 days of life was observed, supporting the concept of different kinetics of immature and adult rat spermatogenesis. Identification of unstained apoptotic cells on the basis of their morphology was as sensitive and reliable as TUNEL staining. The number of apoptotic cells was related to the volume of tissue (i.e., the length of the segment of seminiferous tubule), which enabled quantification of stage-specific apoptosis in the immature rat testis.