Neonatal castration and adult responsiveness to testosterone in male rats: an interstrain comparison

We have previously demonstrated that the spontaneously hypertensive rat (SHR) has a lower central nervous responsiveness to testosterone than its normotensive counterpart the Wistar-Kyoto rat (WKY). The adult psychoendocrine response capacity depends on a neonatal testosterone surge. On that basis, we compared the effects of neonatal endocrine manipulation on the adult responsiveness to testosterone in the SHR, WKY, and yet another breed of Wistar (Wi) male rats. Interstrain differences in testosterone-induced copulatory behavior at three different doses of testosterone propionate (TP) were investigated. Neonatal treatments 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 the 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 differences suggest not only that the adult responsiveness to testosterone is established on the basis of the neonatal gonadal secretion as such but that this secretion is kept to an optimal level with respect to subsequent hormone-sensitive mechanisms.