Female sexual arousal: genital anatomy and orgasm in intercourse

In men and women sexual arousal culminates in orgasm, with female orgasm solely from sexual intercourse often regarded as a unique feature of human sexuality. However, orgasm from sexual intercourse occurs more reliably in men than in women, likely reflecting the different types of physical stimulation men and women require for orgasm. In men, orgasms are under strong selective pressure as orgasms are coupled with ejaculation and thus contribute to male reproductive success. By contrast, women's orgasms in intercourse are highly variable and are under little selective pressure as they are not a reproductive necessity. The proximal mechanisms producing variability in women's orgasms are little understood. In 1924 Marie Bonaparte proposed that a shorter distance between a woman's clitoris and her urethral meatus (CUMD) increased her likelihood of experiencing orgasm in intercourse. She based this on her published data that were never statistically analyzed. In 1940 Landis and colleagues published similar data suggesting the same relationship, but these data too were never fully analyzed. We analyzed raw data from these two studies and found that both demonstrate a strong inverse relationship between CUMD and orgasm during intercourse. Unresolved is whether this increased likelihood of orgasm with shorter CUMD reflects increased penile–clitoral contact during sexual intercourse or increased penile stimulation of internal aspects of the clitoris. CUMD likely reflects prenatal androgen exposure, with higher androgen levels producing larger distances. Thus these results suggest that women exposed to lower levels of prenatal androgens are more likely to experience orgasm during sexual intercourse.     

Methamphetamine enhances paced mating behaviors and neuroplasticity in the medial amygdala of female rats

Methamphetamine (METH) is a psychomotor stimulant strongly associated with increases in sexual drive and behavior in women and men. Even though men and women are equally as likely to be addicted to or use METH, studies of sexual behavior often focus on male users. The paucity in studies examining the effect of METH in women is of great concern, when one considers the high correlation with sexually transmitted diseases such as HIV/AIDS and unplanned pregnancies. In fact, why METH so profoundly increases sexual drive is unknown. We have demonstrated that repeated exposure to METH enhances both receptivity and proceptivity in hormonally primed female rats. The current study examined whether a repeated exposure to METH enhanced female-initiated sexual behaviors in hormonally primed rats. In a paced mating paradigm, METH treatment significantly decreased the female's return latency following a mount (57%) and an ejaculation (44%), and the likelihood to leave the male following an intromission (37%) compared to controls. The METH-induced changes in paced mating behavior were accompanied by a 60% increase in spinophilin levels in the medial amygdala following hormonal priming and METH treatment. Taken together, these findings suggest that METH increases female sexual motivation and behavior in the rat potentially via changes in the neural substrate that require repeated exposure to the drug.     

Forebrain neural patterns associated with sex differences in autonomic and cardiovascular function during baroreceptor unloading

Generally, women demonstrate smaller autonomic and cardiovascular reactions to stress, compared with men. The mechanism of this sex-dependent difference is unknown, although reduced baroreflex sensitivity may be involved. Recently, we identified a cortical network associated with autonomic cardiovascular responses to baroreceptor unloading in men. The current investigation examined whether differences in the neural activity patterns within this network were related to sex-related physiological responses to lower body negative pressure (LBNP, 5, 15, and 35 mmHg). Forebrain activity in healthy men and women (n = 8 each) was measured using functional magnetic resonance imaging with blood oxygen level-dependent (BOLD) contrast. Stroke volume (SV), heart rate (HR), and muscle sympathetic nerve activity (MSNA) were collected on a separate day. Men had larger decreases in SV than women (P < 0.01) during 35 mmHg LBNP only. At 35 mmHg LBNP, HR increased more in males then females (9 +/- 1 beats/min vs. 4 +/- 1 beats/min, P < 0.05). Compared with women, increases in total MSNA were similar at 15 mmHg LBNP but greater during 35 mmHg LBNP in men [1,067 +/- 123 vs. 658 +/- 103 arbitrary units (au), P < 0.05]. BOLD signal changes (P < 0.005, uncorrected) were identified within discrete forebrain regions associated with these sex-specific HR and MSNA responses. Men had larger increases in BOLD signal within the right insula and dorsal anterior cingulate cortex than women. Furthermore, men demonstrated greater BOLD signal reductions in the right amygdala, left insula, ventral anterior cingulate, and ventral medial prefrontal cortex vs. women. The greater changes in forebrain activity in men vs. women may have contributed to the elevated HR and sympathetic responses observed in men during 35 mmHg LBNP.     

黄山短尾猴繁殖的季节性和雌性性活动方式

1987年开始,我们对中国黄山的短尾猴(Macaca thibetana)的性和繁殖行为进行了研究。本文根据1992年全年野外观察,对黄山短尾猴的繁殖季节性和雌性性活动方式进行深入研究,以揭示短尾猴繁殖方式和雌性性行为如何影响雄性性行为。研究采用全事件取样和目标动物取样法。结果表明,短尾猴黄山种群的交配和产仔是季节性的：交配季节发生在7月至12月,其特征是交配频率高并伴有射精;产仔季节为1月至4月。交配季节之外的交配虽有少量发生．但交配频率很低且几乎不射精。成年雌性的会阴部有轻微肿胀的性皮,但性皮的大小和颜色既不随猴群繁殖季节变化,也不随雌性个体生理周期变化。同时,雌性缺乏典型的性要求的行为——发情。因此,我们认为雌性短尾猴倾向于隐蔽自己的排卵。对46个连续观察日中成年雄性对雌性的性行为分析还表明：雄性能够区别潜在繁殖和不繁殖的雌性但不能对同一雌性的生理状况做出准确判断。隐蔽排卵是雌性在性接受期间接受大量交配的主要原因。本研究否定了短尾猴的交配是非季节性的假设(Wadaand Xicmg,1996)[动物学报51(3)：365—375,2005]。     

重度OSAS患者前额叶皮质及岛叶1H—MR波谱研究

目的：利用氢质子MRS（IH-MRS）探讨重度阻塞性呼吸睡眠暂停综合症（Severeobstructivesleepapneasyndrome,S-OSAS）患者前额叶皮质及岛叶脑代谢产物特征。方法：选择18例S-OSAS患者（S-OSAS组）和15名健康志愿者（HC组）行左侧前额叶皮质及岛叶1H-MRS检查,测量两组左侧前额叶皮质区及岛叶N-乙酰天冬氨酸／肌酸（NAA／Cr）、胆碱／肌酸（Cho／Cr）值。对患S-OSAS累计时间与前额叶皮质及岛叶NAA／Cr作直线相关分析。结果：与正常对照组相比,S-OSAS患者左侧前额叶皮质、岛叶NAA／Cr比值降低,分别为1．43±0．47、1．34±0．06,对照组分别为1．51±0．65、1．45±0．07;S-OSAS组患者左侧前额叶皮质、岛叶Cho／Cr分别为0．90±0．08、1．195：0．13,对照组分别为0．87±0．07、1．09±0．02,两组差异有统计学意义。前额叶皮质及岛叶代谢物NAA／Cr与患S-OSAS累计时间成负相关性（r值分别为-0．965、-0．955,P〈0．01）。结论：1H-MRS显示S-OSAS患者前额叶皮质及岛叶病理生理变化,从该区代谢物的改变反应出S-OSAS患者执行及情感功能的异常,其NAA/Cr改变程度与患S-OSAS累计时间相关。     

Effects of sexual stimulation on the sexual performance of rams

The sexual performance of bulls and male goats is improved if they are allowed to view the hetero-sexual behavior of other males as a prelude to mating. The purpose of the following study was to determine whether sexual stimulation enhances the sexual performance of rams. In Experiment 1, 11 sexually experienced ram lambs ( 9 months of age) and 18 sexually experienced yearling and 2-year-old rams were individually exposed to 4 unrestrained, hormone-induced estrous ewes for 60 min after viewing the courtship and mounting behaviors of a male conspecific for 20 min (two tests) and in the absence of stimulator animals (two tests). In contrast to the results with bulls and bucks, the rams were hardly influenced by the sexual stimulation treatment. Latencies for first mount and first ejaculation were shorter for sexually stimulated ram lambs; otherwise, treatment differences were negligible.

A similar follow-up experiment was administered to 12 mature rams using restrained females in the sexual performance tests. Again, treatment differences were minor.

It was concluded that sexual stimulation does not functionally enhance the sexual performance of rams. Species differences in response to sexual stimulation are discussed in terms of female sexual behaviors that may result in a selective (competitive) advantage to males that are stimulated to locate and mate with females early in the estrous period.     

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.     

Hormonal and social factors affecting evoked sexual behavior in Rhesus monkeys

Male rhesus monkey sexual behavior occurring spontaneously or evoked by remotely-controlled hypothalamic stimulation was studied in dominant and subdominant males with both dominant and subdominant, estrogen-treated or untreated, ovariectomized females. The behavior was quantified in terms of number and duration of ejaculatory sequences, number of thrusts, and number of mounts per sequence. Little or no spontaneous sexual behavior was observed with an untreated ovariectomized female. However, evoked sexual behavior with the exception of evoked ejaculation could be obtained whether the females were treated or untreated. Spontaneous and evoked sexual behavior was directed towards both dominant and subdominant females. The female chosen by the male was in part determined by the dominance status of the female. Evoked sexual behavior differed from spontaneous behavior in terms of an increased number of thrusts per mount, an increased number of ejaculations per session, and a decrease in latency between ejaculatory sequences.     

重度OSAS患者前额叶皮质及岛叶1H-MR波谱研究

目的:利用氢质子MRS(1H-MRS)探讨重度阻塞性呼吸睡眠暂停综合症(Severe obstructive sleep apnea syndrome,S-OSAS)患者前额叶皮质及岛叶脑代谢产物特征。方法:选择18例S-OSAS患者(S-OSAS组)和15名健康志愿者(HC组)行左侧前额叶皮质及岛叶1H-MRS检查,测量两组左侧前额叶皮质区及岛叶N-乙酰天冬氨酸/肌酸(NAA/Cr)、胆碱/肌酸(Cho/Cr)值。对患S-OSAS累计时间与前额叶皮质及岛叶NAA/Cr作直线相关分析。结果:与正常对照组相比,S-OSAS患者左侧前额叶皮质、岛叶NAA/Cr比值降低,分别为1.43±0.47、1.34±0.06,对照组分别为1.51±0.65、1.45±0.07;S-OSAS组患者左侧前额叶皮质、岛叶Cho/Cr分别为0.90±0.08、1.19±0.13,对照组分别为0.87±0.07、1.09±0.02,两组差异有统计学意义。前额叶皮质及岛叶代谢物NAA/Cr与患S-OSAS累计时间成负相关性(r值分别为-0.965、-0.955,P<0.01)。结论:1H-MRS显示S-OSAS患者前额叶皮质及岛叶病理生理变化,从该区代谢物的改变反应出S-OSAS患者执行及情感功能的异常,其NAA/Cr改变程度与患S-OSAS累计时间相关。     

Diagnostic d'une anéjaculation

Anejaculation corresponds to absence of ejaculation during orgasm. Most men with anejaculation are aware of their abnormality, but some poorly educated subjects consult for infertility and anejaculation is only suspected on the sperm count. The patient must therefore be questioned about his capacity to ejaculate, for example while sleeping, by masturbation or, less frequently, according to various coital positions. There are various types of anejaculation. Clinical interview is certainly the most important phase of the diagnostic work-up, which is based on analysis of sexual signs and orgasm. It is essential to define the primary or secondary nature of the disorder. After confirming the diagnosis of anejaculation and distinguishing it from retrograde ejaculation and asthenic ejaculation, orgasm without ejaculation and without normal ejaculation outside of coitus must be distinguished from anejaculation without orgasm but with normal ejaculation outside of coitus. The causes of anejaculation may be organic and psychological. The main psychological factors likely to play a role in anejaculation without orgasm can be classified into six categories. However, the presence of one of these factors in a patient with anejaculation does not necessarily imply that it is the cause of the sexual dysfunction; the diagnosis of psychogenic anejaculation is a diagnosis of exclusion after all possible organic causes have been eliminated.     

Characteristic frequency bands of the cortico-frontal EEG during the sexual interaction of the male rat as a result of factorial analysis

The electrocorticogram (ECoG) from the prefrontal cortex was simultaneously recorded with the accelerometric signals of pelvic thrusting performed by male rats during sexual behavior. The changes in the prefrontal ECoG were precisely correlated in time with well defined elements of male rat copulation. Principal component analysis allowed to identify three distinct bands of frequencies in the frontal ECoG: the absolute power (AP) of the 4–16 Hz band was increased in the 500-ms periods before, during, and after the execution of pelvic thrusting in mount, intromission and ejaculation responses; the AP of the 18–24 Hz band was selectively increased during the execution of pelvic thrusting at the three copulatory responses, whereas the AP of the 26–32 Hz band was increased only during the pelvic movements of mount and intromission responses. These results show that the electroencephalographic activity of the prefrontal cortex of the male rat is related to the performance of sexual behavior, supporting the concept that this cortical area is involved in the organization of sequential behaviors, as sexual behavior.     

Neurobiology of sexual behavior

Recent advances in the neurobiology of sexual behavior have helped to refine our understanding of the neuroanatomical, neuroendocrine and neurochemical systems that modulate responses to sexual stimulation. Both appetitive and consummatory sexual behaviors have been studied in several laboratory species and in humans using traditional and novel behavioral paradigms. New knowledge has emerged concerning the role of hypothalamic, limbic and brainstem structures, neuropeptides, brain monoamines and nitric oxide in the control of partner preference, sexual desire, erection, copulation, ejaculation, orgasm and sexual satiety. Brain imaging of visually evoked sexual arousal in humans has also been examined.     

Nuptial flights and calling behaviour in the antLeptothomx acervomm (Fabr.)

Summary We describe in detail a very large nuptial flight of the antLeptothorax acervorum at an open hilltop site in Britain. The mating behaviour of these ants involved not only a large mating swarm but also sexual/calling behaviour by the females. The females left the flight to land on vertical objects, where they took up a characteristic calling posture, in which females of closely related species are known to release pheromones that are sexually attractive to males. ThatLeptothorax acervorum has a complex mating behaviour involving both large nuptial flights and sexual calling has important consequences for the interpretation of the evolution of polygyny in this species and social parasitism in its close relatives.     

Changes of heart rate during sexual behavior in the female rat.

The authors studied the physiological and behavioral responses during sexual behavior in female rats. For this purpose, electrocardiographs were recoded from conscious and unrestrained females using a radiotelemetry system. Heart rate during sexual behavior rose sharply following the introduction of a sexually active male, displayed a peak level of 425 bpm during male ejaculation, and then rapidly decreased. This pattern of heart rate in females before and after receiving ejaculation was similar to that in males before and after ejaculation. In the rate of decrease in heart rate, however, there was a significant difference between females and males. The present study is the first to show changes of heart rate during sexual behavior in female rats.     

Genetic influences on variation in female orgasmic function: a twin study

Orgasmic dysfunction in females is commonly reported in the general population with little consensus on its aetiology. We performed a classical twin study to explore whether there were observable genetic influences on female orgasmic dysfunction. Adult females from the TwinsUK register were sent a confidential survey including questions on sexual problems. Complete responses to the questions on orgasmic dysfunction were obtained from 4037 women consisting of 683 monozygotic and 714 dizygotic pairs of female twins aged between 19 and 83 years. One in three women (32%) reported never or infrequently achieving orgasm during intercourse, with a corresponding figure of 21% during masturbation. A significant genetic influence was seen with an estimated heritability for difficulty reaching orgasm during intercourse of 34% (95% confidence interval 27-40%) and 45% (95% confidence interval 38-52%) for orgasm during masturbation. These results show that the wide variation in orgasmic dysfunction in females has a genetic basis and cannot be attributed solely to cultural influences. These results should stimulate further research into the biological and perhaps evolutionary processes governing female sexual function.     

Face perception is modulated by sexual preference

Face perception is mediated by a distributed neural system in the human brain . The response to faces is modulated by cognitive factors such as attention, visual imagery, and emotion ; however, the effects of gender and sexual orientation are currently unknown. We used fMRI to test whether subjects would respond more to their sexually preferred faces and predicted such modulation in the reward circuitry. Forty heterosexual and homosexual men and women viewed photographs of male and female faces and assessed facial attractiveness. Regardless of their gender and sexual orientation, all subjects similarly rated the attractiveness of both male and female faces. Within multiple, bilateral face-selective regions in the visual cortex, limbic system, and prefrontal cortex, similar patterns of activation were found in all subjects in response to both male and female faces. Consistent with our hypothesis, we found a significant interaction between stimulus gender and the sexual preference of the subject in the thalamus and medial orbitofrontal cortex, where heterosexual men and homosexual women responded more to female faces and heterosexual women and homosexual men responded more to male faces. Our findings suggest that sexual preference modulates face-evoked activation in the reward circuitry.     

Only Self-Paced Mating Is Rewarding in Rats of Both Sexes

When rats are mated in a traditional mating chamber (with one male and one female) in which the male dictates the pace of the copulatory sequence, males develop a reward state as evaluated by conditioned place preference (CPP). In this mating situation no reward state is induced in females. However, when female rats are able to control (pace) the rate of sexual stimulation, thereby reducing the aversive consequences associated with mating, a clear CPP is observed. In the present study the CPP paradigm was used to determine whether if the reinforced state induced by coital interactions in male rats can be maintained when females pace the sexual interaction. Adult male and female rats were mated in one of two different conditions: (1) where subjects were able to pace their coital interactions or (2) where subjects were not able to pace their sexual contacts. The results showed that when males had control over the sexual interaction they developed a clear place preference while males that mated with females that paced their coital contacts did not develop CPP. Similarly, only females that were able to pace their sexual contacts developed place preference. These results suggest that coital interactions in males, as well as in females, can induce a reward state only when they are able to control the sexual interaction. Under seminatural conditions sexual behavior in rats is highly promiscuous, they mate in groups and repeatedly change partners in the middle of copulation. This behavioral sequence allows both, male and female to control the rate of sexual interaction, assuring the induction of a reward state outlasting the actual performance of coital responses.     

A daily rhythm in mating behavior in a diurnal murid rodent Arvicanthis niloticus

The time of day at which mating occurs is dramatically different in diurnal compared to nocturnal rodents. We used a diurnal murid rodent, Arvicanthis niloticus, to determine if inverted rhythms in responsiveness to hormones contribute to this difference. Male and hormone-primed female grass rats were tested for mating behavior at four different times of day (ZT 5, 11, 17, 23; ZT 0=lights-on). In females, there was considerable inter-individual variability with respect to patterns of responsiveness to hormones. Overall, the lordosis quotient (LQ) was rhythmic with a single peak just before lights-on (ZT 23); however, while roughly half of the females (7/15) exhibited this clear daily rhythm, the remaining animals (8/15) had relatively high LQs that did not change as a function of time. Males had their shortest ejaculation latencies and their highest number of ejaculations at ZT 23. Rhythms in mount frequency and post-ejaculatory refractory period were bimodal, with peaks around lights-on and -off (ZT 23 and 11). This temporal pattern of mounting behavior closely parallels previously documented patterns of general activity, whereas rhythms in the more reflexive components of sex behavior (LQ and ejaculation) had more restricted peaks that coincided with just the onset of rhythms in general activity. These rhythms in sexual behavior are essentially reversed relative to those previously documented in lab rats.     

Current concepts in ejaculatory dysfunction

Although erectile dysfunction has recently become the most well-known aspect of male sexual dysfunction, the most prevalent male sexual disorders are ejaculatory dysfunctions. Ejaculatory disorders are divided into 4 categories: premature ejaculation (PE), delayed ejaculation, retrograde ejaculation, and anejaculation/anorgasmia. Pharmacologic treatment for certain ejaculatory disorders exists, for example the off-label use of selective serotonin reuptake inhibitors for PE. Unfortunately, the other ejaculatory disorders are less studied and not as well understood. This review revisits the physiology of the normal ejaculatory response, specifically explores the mechanisms of anejaculation, and presents emerging data. The neurophysiology of the ejaculatory reflex is complex, making classification of the role of individual neurotransmitters extremely difficult. However, recent research has elucidated more about the role of serotonin and dopamine at the central level in the physiology of both arousal and orgasm. Other recent studies that look at differing pharmacokinetic profiles and binding affinities of the alpha(1)-antagonists serve as an indication of the centrally mediated role of ejaculation and orgasm. As our understanding of the interaction between central and peripheral modulations and regulation of the process of ejaculation increases, the probability of developing centrally acting pharmaceutical agents for the treatment of sexual dysfunction approaches reality.     

Conversion of testosterone to estradiol may not be necessary for the expression of mating behavior in male Syrian hamsters (Mesocricetus auratus)

Male sexual behavior is mediated in part by androgens, but in several species, mating is also influenced by estradiol formed locally in the brain by the aromatization of testosterone. The role of testosterone aromatization in the copulatory behavior of male Syrian hamsters is unclear because prior studies are equivocal. Therefore, the present study tested whether blocking the conversion of testosterone to estradiol would inhibit male hamster sexual behavior. Chronic systemic administration of the nonsteroidal aromatase inhibitor Fadrozole (2.0 mg/kg/day) for 5 or 8 weeks did not significantly increase mount latency or reduce mount frequency, intromission frequency, ejaculation frequency, or anogenital investigation relative to levels shown by surgical controls. However, Fadrozole effectively inhibited aromatase activity, as evidenced by the suppression of estrogen-dependent progesterone receptor immunoreactivity in the male hamster brain. The JZB39 anti-progesterone receptor antibody labeled significantly more neurons in brains of sham-treated hamsters than in brains of Fadrozole-treated hamsters. These data suggest that aromatization of testosterone to estradiol is not necessary for normal mating behavior in Syrian hamsters.