Previous sexual experience alters the display of paced mating behavior in female rats

The present study tested whether the display of paced mating behavior in female rats over four weekly tests is affected by sexual experience and whether test parameters, i.e., ending the test based on time or number of stimulations received, influence behavioral changes. In Experiment 1A rats with nonpaced sexual experience returned to the male more quickly overall compared to sexually naïve rats in a 30-min test of paced mating behavior. In Experiment 1B, rats received four weekly 30-min tests with one, different, male rat partner each week. Over the four tests, rats returned to the male significantly more quickly after intromissions, but significantly more slowly after ejaculations. Experiment 2A tested whether sexual experience would influence paced mating behavior in tests with a 15-intromission end criterion and the male replaced after ejaculation. Rats tested weekly under 15-intromission test conditions returned to the male significantly more quickly after intromissions, but no behavioral change was observed after ejaculations. When those same rats were given a 30-min test of paced mating behavior (Experiment 2B), they returned to the male significantly more slowly after ejaculations. Collectively, these data show that sexual experience influences the display of paced mating behavior in female rats and that the test parameters interact with sexual experience to influence the nature of the changes. Sexual experience may facilitate behaviors that promote reproductive success in female rats.     

The effects of prenatal PCBs on adult female paced mating reproductive behaviors in rats

Polychlorinated biphenyls (PCBs) are a family of toxicants that persist in measurable quantities in human and wildlife tissues, despite their ban in production in 1977. Some PCB mixtures can act as endocrine disrupting chemicals (EDCs) by mimicking or antagonizing the actions of hormones in the brain and periphery. When exposure to hormonally active substances such as PCBs occurs during vulnerable developmental periods, particularly prenatally or in early postnatal life, they can disrupt sex-specific patterning of the brain, inducing permanent changes that can later be manifested as improper sexual behaviors. Here, we investigated the effects of prenatal exposure to the PCB mixture Aroclor (A) 1221 on adult female reproductive behaviors in a dose-response model in the Sprague-Dawley rat. Using a paced mating paradigm that permits the female to set the timing of mating and control contact with the male during copulation, we were able to uncover significant differences in female-typical sexual activities in A1221-exposed females. Specifically, A1221 causes significant effects on mating trial pacing, vocalizations, ambulation and the female's likelihood to mate. The results further demonstrate that the intermediate treatment group has the greatest number of disrupted endpoints, suggestive of non-linear dose responses to A1221. These data demonstrate that the behavioral phenotype in adulthood is disrupted by low, ecologically relevant exposures to PCBs, and the results have implications for reproductive success and health in wildlife and women.     

Infusions of naloxone into the medial preoptic area, ventromedial nucleus of the hypothalamus, and amygdala block conditioned place preference induced by paced mating behavior

Paced mating induces positive affect as revealed by conditioned place preference (CPP) in female rats. It has been suggested that endogenous opioids are involved in the generation of this positive affect since systemic administration of the opioid antagonist naloxone blocks mating-induced CPP. Several brain structures, including the medial preoptic area (mPOA), the ventromedial nucleus of the hypothalamus (VMH), the amygdala (Me), and the nucleus accumbens (Acb) have been implicated in the control of female sexual behavior. However, it is not known if these structures also participate in the positive affect produced by paced mating. To this end we determined the effects of intracranial administration of naloxone methiodide into the mPOA, VMH, Me and Acb on conditioned place preference induced by paced mating in female rats. Regardless of the site of infusion 5 μg of naloxone did not affect any of the sexual behavior parameters measured during copulation. When CPP was evaluated, the groups infused with naloxone into the mPOA, the VMH, and the Me before each conditioning session did not develop place preference. Only the group infused with naloxone in the Acb and the control groups did so. These results demonstrate that opioid receptors within the mPOA, VMH and Me are necessary for the rewarding aspects of paced mating. We suggest that the Me and VMH are important for the transmission of sensory information produced by copulation while the mPOA is the site where the positive affect is originated.     

The display of sexual behaviors by female rats administered ICI 182,780

ICI 182,780 (ICI) is a pure antiestrogen that when administered systemically does not cross the blood-brain barrier, thus its actions are limited to the periphery. Four experiments were conducted to test the effects of ICI on the display of sexual behaviors in ovariectomized rats. Experiment 1 examined the effects of three doses of ICI (250, 500, and 750 μg/rat) on sexual receptivity and paced mating behavior in rats primed with estradiol benzoate (EB) in combination with progesterone (P). Experiments 2 and 3 compared the display of sexual behaviors in rats primed with EB+P or EB alone and administered either 250 μg ICI (Experiment 2) or 500 μg ICI (Experiment 3). Experiment 4 tested the effects of ICI (250 and 500 μg) on the expression of estrogen-induced progestin receptors in the uterus. ICI did not affect the display of sexual receptivity in any experiment. In rats primed with EB+P, paced mating behavior was altered by the 500 and 750 μg, but not the 250 μg, doses of ICI. The lowest (250 μg) dose of ICI did alter paced mating behavior in rats primed with EB alone. The effects of ICI on paced mating behavior were manifested by a substantial lengthening of contact-return latencies following intromissions and ejaculations. The percentage of exits were not affected by ICI. Estrogen stimulation of uterine weight and induction of uterine progestin receptors was suppressed by ICI (250 and 500 μg). ICI effects on paced mating behavior in hormone-primed female rats are likely to reflect antiestrogenic actions in the periphery, including interference with the estrogen induction of progestin receptors.     

Hormonal and testing conditions for the induction of conditioned place preference by paced mating

The ability to control or pace the sexual interaction has important physiological and behavioral consequences for the female rat. Paced mating favors reproduction and induces a positive affective state as revealed by conditioned place preference (CPP). In the present experiment we evaluated: 1) If paced mating induces CPP in naturally cycling females; 2) If females developed a positive affective state if they paced the sexual interaction through a 1- or a 3-hole pacing chamber; 3) If females that mate with the same male without pacing the sexual interaction develop CPP. In the first experiment intact females were divided in 4 different groups; 2 paced the sexual interaction until receiving 1 or 3 ejaculations; the other 2 groups mated, without pacing the sexual interaction, until receiving 1 or 3 ejaculations. Only the group that paced the sexual interaction until receiving 3 ejaculations developed a positive affective state. In experiments 2 and 3 hormonally treated ovariectomized females were used. In experiment 2 females were allowed to pace the sexual interaction through a 1- or a 3-hole pacing chamber: A clear positive affective state was induced in both testing conditions. Finally, in experiment 3 females did not develop CPP for non-paced sex despite the fact that they mated with the same male in the conditioning sessions. These results demonstrate that the pattern of vaginocervical stimulation that the females received by engaging in approach and avoidance behaviors to pace the sexual interaction can induce a positive affective state in naturally cycling females. They also confirm the existence of a threshold of vaginocervical stimulation for paced mating to induce CPP in female rats.     

Hormonal status and test condition, but not sexual experience, modulate partner preference in female rats

A series of experiments was conducted to determine the contributions of hormonal status, test condition, and sexual experience to the display of partner preference by female rats. Preference for a sexually active male rat over a sexually receptive female rat was assessed in independent groups of female rats tested in a condition limiting physical contact (No Contact) and a condition allowing for sexual interaction (Contact). Although hormonal status and test condition influenced the preference for a sexually active male, repeated testing and sexual experience had no effect. Experiment 1 demonstrated that independent of test condition, preference for the male is stronger in estrogen- and progesterone-primed rats than in rats receiving the vehicle. Moreover, independent of hormone condition, rats tested in the No Contact condition exhibit a stronger preference for the male than rats tested in the Contact condition, reflecting in part the active pacing of mating stimulation by sexually receptive rats tested in the Contact condition. Experiment 2 showed that the overall pattern of partner preference in proestrous and diestrous rats was similar to that observed in ovariectomized, estrogen- and progesterone-primed, and oil-treated rats, respectively. In Experiment 3, rats primed with estrogen alone did not exhibit a preference for the male even though fully receptive. Experiments 4 and 5 demonstrated that sexual experience does not affect the expression of preference for the male in estrogen- and progesterone-primed rats. The present findings demonstrate that the female rat's preference for the male is stable across repeated tests and is not affected by sexual experience. Our results also confirm that gonadal hormones influence the expression of a preference for a sexually active male versus a sexually receptive female and demonstrate that the magnitude of preference is modulated by test conditions.     

Maternal influences on the sexual behavior and reproductive success of the female rat

In many species, including humans, there is evidence for parental effects on within-sex variations in reproductive behavior. In the present studies we found that variations in postnatal maternal care were associated with individual differences in female sexual behavior in the rat. Females born to and reared by dams that showed enhanced pup licking/grooming (i.e., High LG mothers) over the first week postpartum showed significantly reduced sexual receptivity and alterations in the pacing of male mounting (i.e., longer inter-intromission intervals) observed in a paced mating test. There were minimal effects on the sexual behavior of the male offspring. The female offspring of High LG mothers showed a reduced lordosis rating, a decreased mount:intromission ratio, received fewer ejaculations and were less likely to achieve pregnancy following mating in the paced mating context. The data suggest maternal influences on the sexual development of the female rat that are functionally relevant for reproductive success. Together with previous studies these findings imply that maternal care can ‘program’ reproductive strategies in the female rat.     

Non-intromissive mating stimuli are sufficient to enhance sexual behaviors in ovariectomized female rats

When ovariectomized/adrenalectomized female rats, injected with subthreshold doses of estradiol are given copulatory stimulation by a male rat at half hour intervals, the level of lordosis gradually increases over the course of a few hours. We tested the hypothesis that paracopulatory behaviors (behaviors that occur repetitively prior to and between mounts), also generally considered to be heavily dependent on progesterone, are enhanced by this stimulation as well. We have reported previously that the enhancement of copulatory behavior is dependent to a large extent on intromissive stimulation by the male. In the present study, mating stimulation induced high levels of paracopulatory behaviors, as well as lordosis. Surprisingly, though, and in contrast to previous findings, this increase was seen not only in rats receiving intromissive stimulation, but in those receiving non-intromissive stimulation as well. Furthermore, intromissive stimulation induced high levels of rejection behavior. In a subsequent experiment, experimenter-induced, mechanical stimulation increased only rejection behaviors, not copulatory behavior. The results collectively demonstrate that, under the conditions used in these experiments, non-intromissive stimulation is sufficient for inducing both copulatory and paracopulatory behaviors in estradiol-primed rats. However, under the conditions used in these studies, intromissive stimulation increases rejection behaviors.     

Effects of neonatal testosterone treatment on pacing behaviors and development of a conditioned place preference

Two experiments assessed the effects of neonatal testosterone treatment on paced mating behavior and conditioned place preference in female rats. In both experiments, females received s.c. injections of 5.0 microg testosterone propionate or oil vehicle at three days postpartum. As adults, females were ovariectomized and given s.c. injections of 10 microg estradiol benzoate and 500 microg progesterone, 48 and 4 h before mating, respectively. In Experiment 1, TP- and Oil-treated females exhibited similar high levels of lordosis responsiveness, but TP-treated females showed increased intervals between mounts and between intromissions in paced and non-paced mating conditions compared to control females. The effect was particularly pronounced during paced mating, when contact return latencies were increased approximately 2-fold by TP treatment. TP-treated females showed exaggerated pacing behavior, showing significantly greater return latencies after intromissions than Oil-treated females. In Experiment 2, TP- and Oil-treated groups were tested in a conditioned place preference paradigm to determine if the behavioral changes observed in Experiment 1 were in part a result of changes in the perceived reward produced by paced mating. TP treated and control females developed equivalent preferences for places associated with paced but not non-paced mating, indicating that neonatal TP treatment at this dosage does not disrupt or enhance the conditioned place preference induced by paced mating. The results of the two experiments demonstrate that neonatal TP treatment alters the display of pacing behavior but not the reward state induced by paced mating, and suggest that TP affects neural substrates involved in performance of paced mating without effects on those controlling lordosis or place preference conditioning.     

Influence of time of mating and paced copulation on induction of pseudopregnancy in cyclic female rats

The present experiment was designed to examine whether changes occur during the course of behavioural oestrus in the sensitivity of the female to copulatory stimulation and in patterns of sexual behaviour which might influence the likelihood of luteal maintenance. Cyclic female rats were mated on the evening of pro-oestrus (21:00 h) or early on the morning of oestrus (05:00 h) and received either 5 or 10 intromissions from males under conditions which allowed or did not allow pacing of contacts with males to occur. During mating, the levels of sexual receptivity, the timing of sexual mounts from males, and pacing behaviours were measured. The occurrence of pseudopregnancy or pregnancy in each animal was determined by examining vaginal smears for 14 days after mating and by examining the uterus for the presence of fetuses at the end of the experiment. At both mating times, pacing of copulation with males increased the likelihood of prolonged luteal activity. However, females were more likely to become pseudopregnant following non-paced mating at 05:00 h than at 21:00 h the previous evening. Of those females receiving an ejaculation during mating, no difference were seen between groups in the incidence of pregnancy. This change in sensitivity to cervical-vaginal stimulation during oestrus was not associated with changes in sexual receptivity or pacing behaviour. The ability of cervical-vaginal stimulation to induce pseudopregnancy therefore increases toward the end of the period of oestrus, but the behavioural mechanisms which regulate receipt of such stimulation remain constant during that time.     

The effects of mating stimulation on c-Fos immunoreactivity in the female hamster medial amygdala are region and context dependent

During mating in hamsters, both tactile and nontactile sensory stimulation experienced by the female affect sexual behavior and progestational neuroendocrine reflexes. To test the interactions of these types of mating stimulation, c-Fos immunohistochemistry measured brain cellular activity during sexual behavior under conditions that included combinations of tactile and nontactile mating stimulation. Test groups received: (1) mating stimulation from a male, females being either fully mated or mated while wearing a vaginal mask, or (2) experimenter applied manual vaginocervical stimulation (VCS)-with or without males present, or (3) handling similar to VCS but without insertions-with or without males present. Numbers of c-Fos immunoreactive cells were counted in specific subdivisions of the posterior medial amygdala (MeP) and ventromedial hypothalamus (VMH). The medial amygdala dorsal and ventral subdivisions responded differentially to components of mating stimulation. The posterodorsal Me (MePD) cellular activation was greatest during mating conditions that included VCS and/or males present. However, the posteroventral Me (MePV) was sensitive to male exposure and not to VCS. Also, MePV and VMH shell responses mirrored each other, both being primarily sensitive to male exposure. In separate tests, manual VCS induced pseudopregnancy, though the procedure was most effective with additional nontactile stimulation from males present. In summary, contextual cues provided by nontactile male stimulation enhance the effect of vaginocervical and other tactile stimulation on reproductive processes. Furthermore, c-Fos expression in the female hamster medial amygdala is region and context dependent.     

Different female mating rates in different populations do not reflect the benefits the females gain from polyandry in the adzuki bean beetle

The question why females in many species mate with several males (polyandry) has engaged the interest of evolutionary biologists for many years, and many studies have been conducted on the nature of the benefits that the females gain from polyandry. To understand the variation of female mating rates among species and populations it is indispensable to test the prediction that females of more polyandrous populations experience larger fitness benefit than those of less polyandrous populations. We compared the fitness components of two strains of the adzuki bean beetle Callosobruchus chinensis that have genetically different female mating rates. We measured the number of hatched eggs of once-copulated females and twice-copulated females in each strain. The statistical interaction for the number of hatched eggs between the number of matings and strains was determined. The increase in the number of hatched eggs is larger for the lower mating-rate strain than for the higher mating rate strain. This means that females of the lower mating-rate strain would have larger fitness gain from polyandry than those of the higher mating-rate strain. The actual mating rates of females did not reflect female interests in adzuki bean beetles, suggesting they are affected by sexual conflict.     

三突伊氏蛛雌蛛不同交配史对雄蛛交配行为的影响

近年来越来越多研究表明,雄性产生精子(精液)也需付出代价。在多次交配的动物中,雄性为获得最大生殖潜力,必须依据配偶的质量策略性地调整每次交配的生殖投入。雄性策略性的生殖投入主要体现在两个方面,一是精子竞争(sperm competition),二是柯立芝效应(Coolidge effect)。目前精子竞争研究主要集中于昆虫类群,而柯立芝效应研究集中于高等脊椎动物,同时验证结果也时常与假说不一致。以多次交配的三突伊氏蛛为材料,以雄蛛交配行为为指标,在蜘蛛类群中探讨和验证雄性精子竞争强度假说和柯立芝效应。设定3个交配组合:2只雄蛛依次与1只雌蛛各交配1次(A组)、2只雄蛛依次与2只雌蛛各交配1次(B组)和1只雄蛛与1只雌蛛交配2次(C组),分析比较3个交配组合的三突伊氏蛛第1次交配和第2次交配在交配潜伏期、交配持续时间和交配回合数方面的差异,比较三突伊氏蛛雌蛛不同交配史对雄蛛交配行为的影响,以此验证雄性精子竞争强度假说和柯立芝效应。研究结果表明A和B组的三突伊氏蛛第2次交配的交配潜伏期和交配持续时间显著长于第1次交配。同时,C组的三突伊氏蛛第1次交配的交配潜伏期和交配持续时间与第2次交配都没有显著差异。同时,A、B和C组的三突伊氏蛛第1次交配的交配回合数与第2次交配都没有显著差异。研究结果支持精子竞争强度假说,而不支持柯立芝效应。     

Regulation of sexual odor preference by sex steroids in the posterodorsal medial amygdala in female rats

Our previous study in male rats demonstrated that bilateral administration of flutamide, an androgen receptor (AR) antagonist, into the posterodorsal medial amygdala (MePD) increased the time sniffing male odors to as high as that sniffing estrous odors, eliminating the preference for estrous odors over male odors. This made us speculate that under blockade of AR in the MePD, testosterone-derived estrogen acting on the same brain region arouses interest in male odors which is otherwise suppressed by concomitant action of androgen. In cyclic female rats, endogenous androgen has been thought to be involved in inhibitory regulation of estrogen-activated sexual behavior. Thus, in the present study, we investigated the possibility that in female rats the arousal of interest in male odors is also normally regulated by both estrogen and androgen acting on the MePD, as predicted by our previous study in male rats. Implantation of either the estrogen receptor blocker tamoxifen (TX) or a non-aromatizable androgen 5α-dihydrotestosterone (DHT) into the MePD of ovariectomized, estrogen-primed female rats eliminated preference for male odors over estrous odors by significantly decreasing the time sniffing male odors to as low as that sniffing estrous odors. The subsequent odor discrimination tests confirmed that the DHT and TX administration did not impair the ability to discriminate between male and estrous odors. These results suggest that in estrous female rats estrogen action in the MePD plays critical roles in the expression of the preference for male odors while androgen action in the same brain region interferes with the estrogen action.     

Infusions of naloxone into the medial preoptic area,ventromedial nucleus of the hypothalamus,and amygdala block conditioned place preference induced by paced mating behavior

Paced mating induces positive affect as revealed by conditioned place preference (CPP) in female rats. It has been suggested that endogenous opioids are involved in the generation of this positive affect since systemic administration of the opioid antagonist naloxone blocks mating-induced CPP. Several brain structures, including the medial preoptic area (mPOA), the ventromedial nucleus of the hypothalamus (VMH), the amygdala (Me), and the nucleus accumbens (Acb) have been implicated in the control of female sexual behavior. However, it is not known if these structures also participate in the positive affect produced by paced mating. To this end we determined the effects of intracranial administration of naloxone methiodide into the mPOA, VMH, Me and Acb on conditioned place preference induced by paced mating in female rats. Regardless of the site of infusion 5 μg of naloxone did not affect any of the sexual behavior parameters measured during copulation. When CPP was evaluated, the groups infused with naloxone into the mPOA, the VMH, and the Me before each conditioning session did not develop place preference. Only the group infused with naloxone in the Acb and the control groups did so. These results demonstrate that opioid receptors within the mPOA, VMH and Me are necessary for the rewarding aspects of paced mating. We suggest that the Me and VMH are important for the transmission of sensory information produced by copulation while the mPOA is the site where the positive affect is originated.     

韭菜迟眼蕈蚊雄虫日龄对其交配能力和雌虫生殖力的影响

为了提高韭菜迟眼蕈蚊性信息素监控水平,本文在25℃、RH70%±5%、光周期L∶D=14∶10的条件下研究韭菜迟眼蕈蚊不同日龄雄虫的交配能力及其对雌虫生殖力的影响。结果表明,未交配雄虫平均寿命4.5d,雌虫4.2d,雌雄成虫的平均寿命无显著差异。雄虫一生最多可交配13次,且随着雄虫日龄增加,雌虫交配成功率逐渐减少。随着雄虫交配经历的增加,雌虫交配的时间延长,最长达97min。雄虫的日龄并不影响与之交配雌虫的产卵量和卵孵化率,但是雄虫的交配经历与雌虫的产卵量和卵孵化率相关,尤其当雄虫交配经历超过8次时,与之交配的雌虫的产卵量和卵孵化率显著下降。研究阐明了韭菜迟眼蕈蚊的生殖行为特征,为其性信息素应用提供了参考。     

Response of ERalpha-IR and ERbeta-IR cells in the forebrain of female rats to mating stimuli

Sexual behavior in female rats depends on the action of estradiol on estrogen receptors (ERs) found in particular brain regions. While hormonal regulation of female sexual behavior requires ERalpha, the possible functions of ERbeta remain to be clarified. Mating stimulation has several behavioral and physiological consequences and induces Fos expression in many brain areas involved in the regulation of reproductive behavior and physiology. In addition, some cells in which mating induces Fos expression coexpress ERalpha. To determine whether cells in which Fos is induced by a particular mating stimulus coexpress ERalpha, ERbeta, or both, we used a triple-label immunofluorescent technique to visualize ERalpha-, ERbeta-, and mating-induced Fos-immunoreactivity (Fos-ir) in neurons in which mating stimulation reliably increases Fos expression. Ovariectomized, hormone-primed rats were either unmated, received 15 mounts, or received 15 intromissions. In the rostral medial preoptic area, Fos-ir was induced by mounts alone primarily in cells coexpressing ERalpha-ir, while Fos-ir was induced by intromissions mainly in cells coexpressing both ERalpha-ir and ERbeta-ir (ERalpha/ERbeta-ir). In the dorsal part of the posterodorsal medial amygdala, Fos-ir was induced by intromissions in cells coexpressing ERalpha-ir and ERalpha/ERbeta-ir. However, in the ventral part of the posterodorsal medial amygdala, Fos-ir was induced by intromissions primarily in cells coexpressing only ERbeta-ir. These data suggest that qualitatively different sexual stimuli may be integrated through distinct ER-containing circuits in the rostral medial preoptic area and posterodorsal medial amygdala. The diversity in coexpression of type of ER in cells in different brain areas after various mating stimuli suggests a role for both ERalpha and ERbeta in the integration of hormonal information and information related to mating stimuli.     

Prenatal stress alters reproductive responses of rats in behavioral estrus and paced mating of hormone-primed rats

Adult female offspring of dams exposed to gestational stress (prenatal stress, PNS) may show altered reproductive behavior, exploration in novel environments, and/or social interactions than do their non-PNS counterparts. These behavioral differences may be more readily observed in a seminatural, paced mating paradigm, in which females have greater control of their sexual contacts, than in a standard mating situation. Adult offspring of dams exposed to restraint and lights for 45 min on Gestational Days 14-20 (PNS) were compared with those not subjected to stress (non-PNS, control condition). The motor, reproductive, and sociosexual behaviors of hormone-primed (Experiment 1) or cycling adult offspring in behavioral estrus (Experiment 2) were examined following 20 min of restraint stress under bright lights (postnatal stress). Hormone-primed PNS rats displayed less motor behavior in a novel arena than did non-PNS rats. In a standard mating test, hormone-primed PNS females tended to be more aggressive toward the male than were non-PNS rats. In a seminatural mating situation, hormone-primed PNS females showed increased avoidance behavior, such as longer latencies to the initial intromission, greater return latencies following mounts and intromissions, and more exiting subsequent to mounts and intromissions, than did non-PNS rats. PNS rats in behavioral estrus had decreased incidence and intensity of lordosis, and fewer solicitation behaviors, in both standard or paced mating situations, in which latency to and number of mounts were also increased. Thus, hormone-primed PNS rats exposed to restraint showed more avoidance behaviors in paced mating situations, while cycling PNS rats in behavioral estrus had greater disruption of reproductive responses in standard or paced mating paradigms than did non-PNS control rats.