Catecholamines and the initiation of sexual behavior in male rats without sexual experience.

The purpose of the present experiments was to investigate the effects of modified catecholaminergic neurotransmission upon sexual behavior in inexperienced males. Such males are critically dependent on stimuli from the female in order to initiate sexual behavior, and catecholamines are known to modulate interactions with environmental stimuli. It was found that D-amphetamine, 0.5 and 1 mg/kg, and amfonelic acid, 0.25 and 0.5 mg/kg, reduced mount and intromission latencies. Pimozide, in doses between 0.25 and 1 mg/kg, and cis(Z)-flupentixol, 0.5 mg/kg, reduced the proportion of animals displaying sexual behavior. The noradrenergic neurotoxin DSP4 (50 mg/kg one week before behavioral observation) shortened intromission latency while the noradrenaline precursor threo-dihydroxyphenylserine (10 mg/kg + carbidopa 50 mg/kg) increased mount and intromission latencies. In a test for social and exploratory behaviors it was found that amfonelic acid, in a dose of 0.5 mg/kg, augmented sniffing and rearing without affecting nonsexual interaction with a receptive female. Flupentixol (0.5 mg/kg) had a slight inhibitory effect on exploratory behavior and no effect on nonsexual interaction with a female. It is suggested that enhanced dopaminergic activity facilitates the initiation of sexual behavior due to an increased general arousal and not because of a specific effect on that behavior. The role of noradrenaline is less clear at present.