[en] Female rats given a single injection of testosterone propionate (TP) in the first few days of post-natal life exhibit post-pubertally, persistent vaginal oestrous, sterility, disordered secretion of gonadotrophins and modified patterns of sexual behaviour. The effects of TP on the incorporation of ¹⁴C-uridine in the CNS of 5 and 61/2 day old litter mate triads consisting of male, female and TP treated female rats were investigated. Low resolution autoradiographs of serial sections of brain were prepared and analysed. A sexual dimorphism in cell nuclear size was found in the suprachiasmatic, arcuate and paraventricular nuclei of the hypothalamus. TP treatment resulted in an increase in nuclear size towards the male pattern in the latter two areas. A decrease in cell nuclear size was found in the ventromedial and suprachiasmatic nuclei. Neither sex differences nor changes following TP injection were detected in rate of incorporation of ¹⁴C-uridine in any areas of the brain, although a significant (p<0.02) reduction in uridine incorporation in the adrenal of the female animal 24 hours after TP injection was demonstrated. The results suggested an immediate direct action of TP on the hypothalamus and peripheral tissues of the neonatal rat. (author)