Initiation of copulatory behaviour in castrated male rats implanted with very small testosterone-filled silastic capsules.

Adult, sexually experienced male rats were castrated and two weeks later implanted with 5 or 10 mm long testosterone-filled silastic capsules (inner diameter 1.4 mm). From the seventh up to the fourteenth week following implantation the majority of males was found to be in the state at which they initiated copulatory behaviour with proceptive (darting) females but not with passively receptive (lordotic) females. Being in this state, their copulatory performance was comparable with precastration level except the decreased frequency of intromission befor the first ejaculation. As to the precopulatory behaviour, the males displayed it even towards females which did not stimulate copulatory behaviour in these males. In all the applied measures no difference between the 5 and 10 mm capsules was revealed. The used implants were found behaviourally effective about fourteen or nineteen weeks throughout following implantation or reimplantation, respectively.