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Introduction It has been demonstrated that testing conditions may influence sexual performance in many mammals, including male rats. We recently developed a multiple partner choice arena (MPCA) consisting of four acrylic cylinders placed in a cross pattern with one male in each cylinder. A sexually receptive female rat was introduced into the center of the MPCA and was allowed to choose a male to copulate with. The female showed a preference for one of the four males, remaining longer and copulating more times with it. Aim The study aims to evaluate and compare the copulatory pattern of male rats in two arenas: the standard arena (SA) and the MPCA. Methods In Experiment 1, a group of 10 male rats mated in an SA (a closed cylinder) and 2 weeks later they mated in the MPCA, in order to compare different parameters of male sexual behavior. In Experiment 2, the sexual behavior of two different groups of sexually experienced male rats was tested in two conditions: the SA and the MPCA. In the latter, only the behavior of the preferred (P) males and nonpreferred (NP) males that ejaculated was recorded. Main Outcome Measures The main outcome is the number of intromissions preceding ejaculation and the latencies to mount, intromit, and ejaculate. Results In Experiment 1, the number of intromissions was significantly reduced and the intromission and ejaculation latencies were significantly shortened when the males were tested in the MPCA rather than in the SA. In Experiment 2, both groups of males tested in the MPCA (P and NP) showed a significant reduction in the number of intromissions preceding ejaculation and shorter mounting and ejaculation latencies in comparison with rats in the SA. This decrease was more noticeable in NP males. Conclusions The MPCA reduce significantly the ejaculatory pattern in male rats.

Introduction The multiple partner choice arena (MPCA) is an experimental setup in which male rats display a significant shortening of ejaculation latency, which is the main characteristic of premature ejaculation (PE) in men. Thus, the MPCA is a potential animal model for PE. Aim In this study, we further analyze whether the features of the MPCA satisfy the validity criteria for it to be considered an animal model as well as the possible participation of the serotoninergic system in the faster ejaculation exhibited by male rats in the MPCA. Methods In Experiment 1, male rats were tested in a standard arena to assess their sexual behavior, then were assessed 1 week later in the MPCA. Another group was first tested in the MPCA, then in a standard arena. In Experiment 2, male rats divided into two groups were treated daily with WAY-100635 (5-HT1A antagonist) or vehicle for 15 days. In each group, half of the subjects were tested in a standard arena and half were tested in the MPCA on days 1, 8, and 15 of treatment. Main Outcome Measures Number of intromissions and intromission and ejaculation latencies were the main outcome measures. Results In Experiment 1, males tested in the MPCA ejaculated significantly faster, regardless of the order in which they were evaluated in both arenas. In Experiment 2, the administration of WAY-100635 increased intromission and ejaculation latencies, and the number of intromissions in the MPCA. Conclusions The results obtained in the MPCA support its use as an animal model for PE evaluation.

The aim of this work was to compare the effect of neonatal treatment with the phytoestrogens coumestrol (COU) and genistein (GEN), administered in equimolecular doses, on the sexual behavior and partner preference of male rats. Four groups of male rats were injected daily from day 1 to 5 with 150 µg of GEN, an equivalent amount of COU, 1 µg of β-estradiol 3-benzoato (EB), or olive oil (VEH) (control). A fifth group remained intact. In the GEN group, intromission and ejaculation latencies decreased, whereas ejaculatory frequency increased. Contrasting results were observed in COU males. EB males could not ejaculate and their mount and intromission latencies increased significantly. To determine sexual-partner preferences, a multiple partner preference arena was used and two types of tests were performed, the first one without allowing contact test (CT) with the stimulus animals, followed by a CT. COU and GEN groups did not show preference for any stimulus animal, whereas the EB males preferred the expert male. When CT with the stimulus animals was allowed, GEN-males preferred the receptive female, unlike the COU and EB groups. It is concluded that neonatal treatment with COU and GEN induced opposite effects, the effects of COU being more estrogenic.