Histochemical tracing of zinc ions in the rat testis

To detect free zinc ions in the rat testes four rats were transcardially perfused with Na2S, and the seminiferous tubules from two other rats were incubated in Na2S. Sections from the two sources were autometallographically (AMG) developed, whereby zinc sulphide crystal lattices created in the tissue by the sulphide treatment were silver enhanced. Light microscopical analysis showed zinc ions in primary spermatogonia until the zygotene primary spermatocytes (stage I), in late pachytene spermatocytes (stages XII and XIII), and in late spermatids from step 15 to step 19 (stages I-VIII). The highest intensity of AMG grains was detected in the residual bodies and tails of step 19 spermatids. Grains were occasionally found in the cytoplasm of Leydig cells. Sections from animals treated with the chelator diethyldithiocarbamate prior to sulphide treatment showed a complete lack of AMG staining. At ultrastructural levels the AMG grains were found in smooth-surfaced endoplasmic reticulum of all spermatogonial stages, and in the acrosome, midpiece, and tail of late spermatids. The presence of zinc ions in preleptotene spermatocytes and cytoplasmic lobes of late spermatids suggests a specific role of free zinc at the onset of meiosis and at spermiation.