Twelve male rats were left with receptive females and allowed to copulate and ejaculate until they reached a criterion of “sexual exhaustion” They were then retested after 1, 3, 6 and 15 days of sexual inactivity. Following these observations males were tested once each day or once every other day and allowed to achieve a single ejaculation. In the course of a period of unlimited access to the receptive female males usually need approximately 10 intromissions to produce the initial ejaculation, but successive ejaculations are produced by fewer and fewer intromissions. The time to recover from the effects of an ejaculation increases progressively as exhaustion is approached. Very few animals copulate when tested 24 hours after sexual exhaustion. Considerably more recovery is evident in tests conducted after a 3-day rest, but it is not complete and rats are not capable of achieving as many ejaculations as they tend to achieve after longer periods of inactivity. As measured by ejaculation-frequency, the curve of sexual recovery is negatively accelerated and probably reaches asymptote after 7 to 10 days of rest. Various other measures in addition to ejaculation-frequency support this conclusion. Males allowed to ejaculate once each day or every other day are somewhat less responsive than fully rested animals, but do not show any progressive loss in sexual excitability or capacity. A working hypothesis is proposed to explain most of the findings. It postulates the existence of an Arousal Mechanism which is distinct from a Copulatory Mechanism. The ways in which these hypothetical mechanisms are affected by sexual performance and sexual rest arc discussed.

The first, study of "sex drive" in male rats was that of Moss (11), who measured the frequency with which males would cross an electrified grid to reach a female. In subsequent experiments Warner (16), Jenkins (9), and Nissen (12) employed the Columbia Obstruction Apparatus as an indicator of "sex drive" in both male and female rats. These early investigations suffered from various methodological defects and did not include adequate measurements of copulatory behavior. Stone, Barker, and Tomlin's study of male rats revealed that correlations between copulation scores and performance in the Columbia apparatus ranged from +0.33 to +0.40 (15).In the investigation of other drives, time to run down a straight alley has proved a useful measure. Hull (8) and Miller and Miles (10) demonstrated a relationship between food or water deprivation and the speed with which rats will traverse a runway when the appropriate reward is available in the goal box. Sheffield, Wulff, and Backer (13) reported that male rats will run down an alley to reach a receptive female, and that the speed of males which copulate with the female is faster than that of noncopulating individuals.The present experiment was conducted to study the relations between running speed and copulatory performance in male rats, and to investigate the effects of castration followed by androgen treatment. METHOD SubjectsNine, 90-day-olcl, hooded male nils were chosen as .S' s on the basis of their performance in preliminary mating tests. All demonstrated high sexual responsiveness by copulating and ejaculating in four tests with receptive females. Males were kept in individual cages, and all animals were housed and tested in a room that was artificially illuminated at night and darkened