The synthetic activity of primordial germ cells in normal and irradiated neonatal male rats.

Resting primordial germ cells or gonocytes, present in the testis of the rat at birth (Beaumont & Mandl, 1963), are highly radiosensitive. A dose of 50-100 r X-rays induces complete, or almost complete, sterility, as judged by the histological appearance of the testis at 25 days post par turn (Mandl et al. 1964). Studies of short-term post-irradiation changes have revealed that gonocytes, exposed to a sterilizing dose of X-rays at birth, do not degenerate immediately after exposure but differentiate normally into transitional cells (the immediate precursors of definitive germ cells; Beaumont & Mandl, 1963; Huckins, 1963; Franchi & Mandl, 1964) so that no histological abnormalities are detectable for 5 or 6 days. Subsequently, however, the irradiated transitional cells fail to divide; they increase markedly in size and form irregularly shaped giant cells which eventually become pyknotic (Franchi & Mandl, 1966; see also Sapsford, \965a). Thus by 8 days post par turn (p.p.) a number of changes are apparent in the testes of irradiated animals. At this time normal animals contain transitional cells (some of which are dividing) and spermatogonia type-A, whereas the gonads of treated specimens are populated by gonocytes, giant transitional cells and pyknotic germ cells. These observations suggest that irradiation.blocks the mitotic division of transitional cells, thus preventing the formation of spermatogonia type-A, without inhibiting the synthesis of cellular constituents (see Franchi & Mandl, 1966). The present study was undertaken in order to examine and compare, by means of autoradiography, some of the metabolic processes of the nuclei of gonocytes and transitional cells in the testes of normal and irradiated rats aged 2-8 days p.p. The experiment was designed to determine whether the formation of giant transitional cells was correlated with changes in the pattern of synthesis of DNA, RNA and nucleoprotein. 1 Author's address: The Department of Anatomy, The Medical School, Birmingham 15, Great Britain.