Penile responses of rats (Rattus norvegicus) in extended ex copula tests

Prolonged tests of rats' penile responses outside the context of copulation (ex copula) were undertaken to facilitate analysis of these penile components of copulatory behavior. Penile erections and flips were evoked for 1 hr following penile sheath retraction (SR), and rats were retested for 30 min after a rest interval of 5 min to 4 hr. The number of penile responses declined sharply over the course of the hour. Following a 5-min rest, there was little likelihood of additional responses. Within 2 hr some measures of penile response potential approached their original high asymptotes; other measures were still depressed after 4-hr rest. In control tests, the penile sheath was unretracted (SU) during the first 60 min, and hence few or no penile responses occurred. This condition caused no reduction in the number of erections and flips in the subsequent 30-min SR test; hence the reduction in response potential during and after SR tests was due to the responses displayed, not to the conditions of restraint. Ejaculation occurred frequently in the SU condition but rarely in SR tests, results suggesting that sheath retraction may normally inhibit ejaculation in ex copula tests, and perhaps during copulation as well.