Effects of neonatal treatment with two phytoestrogens on male rat sexual behavior and partner preference.

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 ß-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.

Further definition on the multiple partner choice arena: a potential animal model for the study of premature ejaculation.

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-HT(1A) 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 mild stress of chronic prenatal injections may have additive effects on drugs administered during pregnancy to alter brain sexual differentiation.

OBJECTIVE: In order to clarify the effect of the prenatal (PN) treatment of the drug 1,4,6-androstatriene-3,17-dione (ATD) which blocks the conversion of testosterone into estradiol on male sexual behavior of the rats offsprings, from the effect of the mild stress induced by the PN administration of the Propylene glycol (PG), the vehicle used to dissolve ATD. METHODS: Pregnant Wistar rats were divided into three groups. The CON group did not receive any kind of treatment. The other two groups (PG and ATD) were injected i.p. during gestation (days 11-22) with 0 and 5 mg of ATD, dissolved in 0.1 ml of PG, respectively, doses reported by other authors. Sexual performance of the male pups was analyzed three months later in four successive tests. RESULTS: In the first sexual test of these naive rats, the percentage of males mounting, intromitting, ejaculating and the ejaculation frequency of the ATD group decreased significantly in comparison with the CON group. Also in the first and 4th tests, mounting, intromission and ejaculation latencies, as in the post-ejaculatory refractory period, ATD group, was significantly longer in comparison with the CON group. PG males showed a male sexual behavior (MSB) similar to that observed in the ATD group, but the differences did not reach statistical significance when they were compared with the CON group. CONCLUSION: We considered that the PN stress induced by the daily administration of PG and ATD, results in a slower execution of the MSB in both groups and avoid distinguish the effect of the ATD. Then chronic PN injections, as a route of administration, could act as mild stressor and may have additive effects on drugs affecting brain sexual differentiation.

Copulatory pattern of male rats in a multiple partner choice arena.

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.

Testosterone levels and histological features of reproductive glands in adult male rats treated neonatally with tamoxifen.

OBJECTIVE: In this study we examined the possibility that demasculinization produced by the neonatal administration of tamoxifen is accompanied by a decline in plasma levels of testosterone during adulthood. METHODS: Wistar male rats received either a treatment with 12.5 microg/kg of tamoxifen during the first eight days of age or a treatment with 100 microg/kg of tamoxifen for five days. Each treatment had their respective control group. During adulthood their masculine sexual behavior was analyzed. At 8 months of age, males were killed by decapitation, trunk blood was collected and peripheral glands were dissected and weighed. Testosterone levels were measured by HPLC. Histological analysis of peripheral glands was performed. RESULTS: Both neonatal tamoxifen treatments significantly decreased male sexual behavior when compared to control values. In addition, both treatments also showed a significant decrease in testicular weight when compared to control groups, as well as a decrease in seminal vesicle weight. In the microscopic analysis, a significant decrease in the diameter of the seminiferous tubules was observed, especially in the animals treated with 100 microg/kg of tamoxifen. However, no differences were observed between tamoxifen treated and control animals concerning plasma levels of testosterone. CONCLUSION: The present results indicate that behavioral manifestations and changes in peripheral reproductive organs that accompanied demasculinization are not due to a deficit in testosterone secretion.