Effects of lisuride on precopulatory and copulatory behaviour of adult male rats.

Lisuride (12.5, 125, 250, 400, 600, 800 micrograms/kg) injected IP 40 min prior to observation of adult, but sexually inexperienced, male rats (a) caused a dose-dependent increase in motor activity, (b) suppressed rearing completely at doses of 125 micrograms/kg and above, and (c) caused a dose-dependent increase of specific sniffing of the scent traces of an estrous female, the sniffing lasting the whole duration of a 5-min test at 800 micrograms/kg. In the presence of a passively receptive (lordotic) female, the amount of time devoted to sniffing of the scent traces decreased but was still dose-dependent. The males exhibited relatively more precopulatory behaviour towards the female at 400-800 micrograms/kg. The number of males initiating copulatory behaviour was small and comparable with saline-injected controls. When exposed to sexual stimuli from a weakly soliciting (presenting posture) female the number of lisuride-treated males (250 and 400 micrograms/kg doses were used) initiating copulation was higher in comparison with the controls. At the same time the males began to copulate mostly with short latencies and without any precopulatory behaviour towards the female. The lisuride-treated males reached ejaculation after a very small number of intromissions. The effects of lisuride are discussed from the point of view of lowered behavioural thresholds of the males to specific and distinct stimuli.