NEONATAL CASTRATION AND ADULT RESPONSIVENESS TO TESTOSTERONE IN MALE RATS - AN INTERSTRAIN COMPARISON

We have previously demonstrated that the spontaneously hypertensive ra t (SHR) has a lower central nervous responsiveness to testosterone tha n its normotensive counterpart the Wistar-Kyoto rat (WKY). The adult p sychoendocrine response capacity depends on a neonatal testosterone su rae. On that basis, we compared the effects of neonatal endocrine mani pulation on the adult responsiveness to testosterone in the SHR, WKY, and yet another breed of Wistar (Wi) male rats. Interstrain difference s in testosterone-induced copulatory behavior at three different doses of testosterone propionate (TP) were investigated. Neonatal treatment s were as follows: TP (0.25 mg/animal) given on postnatal days (PND) 0 , 2, and 4 (SHR and Wi only) or castration PND 0, 10, or 50. Neonatal TP treatment impaired copulatory performance in the adult SHR but not in the Wi. Neonatal castration improved the responsiveness to TP in th e SHR but less so in WKY, whereas no evident effects were seen in the Wi. No significant interstrain differences in plasma testosterone were observed 2, 6-12, or 24 h postpartum. The demonstrated interstrain di fferences suggest not only that the adult responsiveness to testostero ne is established on the basis of the neonatal gonadal secretion as su ch but that this secretion is kept to an optimal level with respect to subsequent hormone-sensitive mechanisms. (C) 1997 Elsevier Science In c.