The relationships and distribution of spermatogonia were studied as a function of the stage of the seminiferous epithelium cycle in rats. Primitive spermatogonia in the mouse are located along regions of the basal lamina that face the interstitium. Before studying the distribution of spermatogonia in rats, it was necessary to characterize the various types of spermatogonia, as recently performed for mice. The Strauss' linear index (Li) selectivity method was then used and spermatogonia of the A(single) (A(s)) to A(aligned) (A(al)) lineage were preferentially found to be located in regions opposing the interstitium at stages V, VII and IX of the spermatogenic cycle. Because relatively little tubule-to-tubule contact occurs in rats, the aim of this study was to determine whether tubule-to-tubule contact or tubule proximity (or alternatively, the amount of interstitium) was an important factor in spermatogonial position. In this regard, another method (tubule proximity) was devised to determine spermatogonial position that accounted for the presence of adjacent tubules. This method showed that the position of tubules, rather than tubule contact, was more accurate than the Li method in determining the location of spermatogonia in the rat. The results also showed a non-random distribution of spermatogonia resembling that of the mouse, and that tubule-to-tubule contact is not essential for the positioning of spermatogonia. In conclusion, the results of this study strongly indicate that the most primitive type A spermatogonia (A(s), A(paired) and A(al)) in rats are present in niches located in those areas of the seminiferous tubules that border the interstitial tissue.
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