Testis, Seminiferous Tubule - Retention, Spermatid

Spermiation (the release of fully mature spermatids into the tubular lumen) normally occurs during stage VIII of the spermatogenic cycle in rats and mice. Numerous toxicants have been shown to disrupt spermiation, resulting in the continued presence of the mature spermatids (step 19 spermatids in the rat, step 17 in the mouse) at the luminal surface of stage IX-XI tubules (Figure 1 and Figure 2). The retained spermatids are then pulled down into the basal Sertoli cell cytoplasm, where they are phagocytized. Spermatid retention has been described following exposure to a number of chemicals, including boric acid, 2,5-hexanedione, and dibromoacetic acid. Spermiation is testosterone dependant, so spermatid retention also occurs with decreased intratesticular levels of testosterone. Although subtle, this finding is important to recognize and record since it usually results in reduced epididymal sperm count, sperm abnormalities, and potential effects on fertility. A few retained spermatids can often be seen at the lumen of stage IX tubules or phagocytized at the base of stage XII tubules, but they are generally very few in number and restricted to one or two tubules.