Copulation and ejaculation in male rats under sexual satiety and the Coolidge effect.

Sexually satiated males cease copulating after several ejaculations with the same female; and the presence of an unknown receptive female renews copulation including ejaculation, a process named the Coolidge effect. It is believed that the Coolidge effect has the aim to impregnate another female, although it is known that the sperm count gradually decreases after consecutive ejaculations. The main goal was to investigate if sexually satiated males during the Coolidge effect can reestablish seminal expulsion associated to the ejaculation behavior and/or penile erection associated to the intromission behavior. The results show that during the Coolidge effect, most of the sexually satiated males showed the motor ejaculatory behavior, however, no sperm in the uterine horns or seminal plug in the vagina were detected. Such lack of sperm was not related with the number of ejaculations required to achieve sexual satiety nor with the number of intromissions needed for ejaculating (experiment 1: 2.4.1.). After the behavioral ejaculation, during the Coolidge effect, there was a 44% decrease in sperm count in the epididymal caudae (experiment 1: 2.4.2.). Males that mated for 8 behavioral ejaculations (close to sexual satiety) deposited tiny seminal plugs but no sperm in the female reproductive tract (experiment 1: 2.4.3.). Interestingly, sexually satiated and non-satiated-animals displayed similar number of intromissions and spent a similar time in dislodging the seminal plug from the vagina deposited by other males (experiment 2). These results suggest that sexually satiated males during the Coolidge effect have the capacity for penile erection and vaginal insertion, because they are able to dislodge seminal plugs; but are unable to expel seminal fluid, because neither form seminal plugs nor deposit sperm in the female genital tract.