SPONTANEOUS SEMINAL EMISSION IN THE RAT AND ITS RELATIONSHIP TO PENILE REFLEXES AND COPULATORY BEHAVIOR

Spontaneous seminal emission (SSE) in the rat occurred almost exclusively in the light period (14:10 light/dark cycle). Following a lighting reversal, the circadian pattern of SSE shifted gradually over a period of three weeks. Similarly, diurnal variation in ejaculation latency (EL) and interintromission interval (III) was not re-established until the third week post-reversal, whereas the variation in intromission latency (IL) shifted within one week. The display of penile reflexes showed no differences with respect to time of day.

There was a gradual decline in the incidence and frequency of SSE following castration. This was prevented by concomitant implantation of 30 mm Silastic capsules containing dihydrotestosterone (DHT) and also reversed in long-term castrates (2 months postgonadectomy) by DHT implantation.

The incidence and frequency of SSE did not differ between sexually naive and experienced rats, or between sexually inactive (noncopulators) and sexually active rats. There was also no difference in SSE activity between rats with medial preoptic area (MPOA) lesions and sham-lesioned controls, or between animals bearing corticomedial amygdala or sham lesions. Likewise, penile reflex activity did not differ significantly between any of these groups, with the single exception of an increased number of quick flips after MPOA lesions.

Midthoracic spinal cord transection had no significant effect upon SSE, but enhanced the display of penile reflexes. Acute administration of a potent dopamine agonist, RDS-127 (3 mg/kg), induced seminal emission within 5 minutes by spinally-intact and transected rats. (RDS-127 was previously shown selectively to lower the ejaculatory threshold in copula.) RDS-127 virtually abolished the display of penile reflexes by intact rats and reduced the number of reflexes of spinal rats to intact levels.

Acute (5 or 25 mg/kg) or chronic (daily, 5 mg/kg) treatment with the sympathetic (adrenergic) blocking agent, guanethidine, totally abolished seminal emission in and ex copula, and severely depressed plasma testosterone levels, without markedly affecting copulatory performance. Penile reflexes were also unaffected by guanethidine, except for an increased number of long flips 4 hours after acute (25 mg/kg) treatment.

Finally, there was no difference in SSE activity between young (5 month) and old (23 month) rats. The number of erections in the penile reflex test, however, was lower in old rats.