Sperm count and sperm motility decrease in old rats.

Sexual behavior declines with age in male rats. The rate and magnitude of this decline may depend on the amount of prior sexual experience and a number of other, unidentified factors. Age-dependent changes in the characteristics of ejaculate quality in rats have not been described earlier, and the relationship between such changes and modifications of sexual behavior is likewise unknown. We have recently developed a technique for the detailed analysis of parameters of ejaculate in rats, and this technique was used for the determination of semen and seminal plug characteristics in rats of different ages. Sexually experienced Wistar rats were tested for sex behavior at the ages of 3, 12 and 24 months. Semen was obtained from the female partner immediately after ejaculation at these tests. Between tests, the males were offered the opportunity to copulate once every 3-4 weeks. The behavioral data showed that the latency to ejaculation was increased only at 24 months. Concerning the characteristics of semen, there was a substantial increase in the proportion of immobile spermatozoa and motility of those moving was much reduced, both at 12 and 24 months of age. There was no relationship between parameters of sexual behavior and those of the ejaculate. Likewise, the size of the seminal plug did not affect the amount of intrauterine spermatozoa. The reduced sperm number together with the increased sperm immobility diminishes the ejaculate quality of old males, which could influence fertility.

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.

Rat dorsal prostate is necessary for vaginal adhesion of the seminal plug and sperm motility in the uterine horns.

The rat prostate comprises dorsal, ventral and lateral lobes that are morphologically and biochemically distinct. Lesions to these structures are expected to affect the quality of the ejaculate and male fertility. In experiment 1, we analyzed ejaculate parameters of males that had chemical lesions of the dorsal or ventral lobes. At pre-lesion and at 5 and 20 days post-lesion males were mated, and after ejaculation, seminal fluid and seminal plug were obtained from the mated females. In experiment 2, the ventral lobes were ablated, and the ejaculate was analyzed. In experiment 3, the fertility of males with chemically-lesioned dorsal lobes or ablation of the ventral lobes was evaluated. Chemical lesion of the dorsal lobe prevented the adhesion of the seminal plug to vaginal walls. When these males were tested at 5-days postlesion, no sperm were found in uterus, and at 20-days post-lesion, the few sperm encountered showed slow progressive motility. None of the females that mated with dorsal lobe-lesioned males became pregnant. However, chemical lesion or ablation of the ventral lobes did not affect ejaculate or fertility. Our results indicate that the dorsal prostatic lobes are indispensable for reproductive success in males, and define parameters of ejaculate with which fertility can be estimated.

Rat dorsal prostate is necessary for vaginal adhesion of the seminal plug and sperm motility in the uterine horns

The rat prostate comprises dorsal, ventral and lateral lobes that are morphologically and biochemically distinct. Lesions to these structures are expected to affect the quality of the ejaculate and male fertility. In experiment 1, we analyzed ejaculate parameters of males that had chemical lesions of the dorsal or ventral lobes. At pre-lesion and at 5 and 20 days post-lesion males were mated, and after ejaculation, seminal fluid and seminal plug were obtained from the mated females. In experiment 2, the ventral lobes were ablated, and the ejaculate was analyzed. In experiment 3, the fertility of males with chemically-lesioned dorsal lobes or ablation of the ventral lobes was evaluated. Chemical lesion of the dorsal lobe prevented the adhesion of the seminal plug to vaginal walls. When these males were tested at 5-days postlesion, no sperm were found in uterus, and at 20-days post-lesion, the few sperm encountered showed slow progressive motility. None of the females that mated with dorsal lobe-lesioned males became pregnant. However, chemical lesion or ablation of the ventral lobes did not affect ejaculate or fertility. Our results indicate that the dorsal prostatic lobes are indispensable for reproductive success in males, and define parameters of ejaculate with which fertility can be estimated.