Revisiting post-ejaculation refractory time-what we know and what we do not know in males and in females

Repeated sexual intercourse as a coping strategy for men with premature ejaculation

BACKGROUND

Patients with premature ejaculation (PE) are often concerned and distressed about their sexual performance. Hence, they may be more willing to exploit their refractory period to employ sexual coping strategies in order to improve their unsatisfactory sexual intercourse compared with patients without PE.

AIM

The study sought to verify the sexual coping strategies of patients with PE in the daily sexual activities.

METHODS

We included both patients with PE and individuals without PE and analyzed their sexual behaviors and attitudes by means of detailed interviews and questionnaires.

OUTCOMES

The main outcomes were perceived intravaginal ejaculatory latency time recording, Premature Ejaculation Diagnostic Tool score, and sexual frequency, attitudes, and behavior log.

RESULTS

A total of 182 young patients with PE (age 31.2 ± 6.2 years) and 92 individuals without PE (age 30.7 ± 5.1 years) were included in the study. A total of 53.3% of patients with PE vs 17.4% of individuals without PE reported engaging in multiple sexual intercourse sessions within a single day in the past 4 weeks. PE patients who engaged in multiple intercourse sessions displayed better performance during the second attempt but performed poorly compared with individuals without PE. Scores for the first attempt in PE vs second attempt in individuals with PE vs without PE were the following: intravaginal ejaculatory latency time, 2.4 ± 1.6 vs 4.8 ± 5.7 vs 9.9 ± 9.4 (P < .001); Premature Ejaculation Diagnostic Tool, 14.9 ± 3.1 vs 12.7 ± 4.8 vs 5.2 ± 2.5 (P < .001); satisfaction, 2.9 ± 1.0 vs 3.1 ± 0.8 vs 3.7 ± 1.4 (P < .001). A total of 57.1% of patients held a negative attitude toward precoital masturbation, for reasons such as a reduced sexual desire (21.2%), the belief that masturbation is harmful (17.6%), concerns about erectile function (15.7%), fatigue (9.8%), and other mixed reasons (35.3%).

CLINICAL IMPLICATIONS

Engaging in multiple intercourse sessions within a day is more common among the young PE population, and using precoital masturbation as a coping strategy is not universally applicable among patients with PE.

STRENGTHS AND LIMITATIONS

This is the first study to explore symptom-coping strategies in patients with PE compared with individuals without PE. However, the conclusions cannot be generalized to the entire male population.

CONCLUSION

Patients with PE, compared with individuals without PE, are more inclined to engage in multiple sexual intercourse sessions within a single sexual session, likely in an attempt to compensate for their first unsatisfactory sexual encounter. Moreover, the majority of patients with PE here studied hold a negative attitude toward using precoital masturbation as a coping strategy for symptoms.

An economon model of drug addiction

The term "economon" (i:'ka.nə.muhn; plural: economa) is introduced here to describe an economic unit composed of two participants engaged in mutually reinforcing operant behavior. Economa are basic building blocks of transactional behavior that aggregate in social networks called economies. In a drug-addiction economon, operant behavior by one participant (the "supplier") provides an addictive drug as a reinforcer to the second participant (a "Person with Substance Use Disorder; PwSUD"). Reciprocal operant behavior by the PwSUD usually provides money as a reinforcer to the supplier. After defining the features of the drug-addiction economon, this article discusses its implications for (1) prevalence and virulence of drug addiction, (2) opportunities for drug-addiction research in general, (3) the "brain-disease model of addiction" in particular, and (4) factors that mitigate harm or promote risk of drug addiction. The economon model is intended to provide a novel perspective on the uniquely human disorder of drug addiction.

Semen collection and ejaculation trigger changes in the blood flow of the reproductive system in rams

The aim of this study was to determine if ejaculation modifies the testicular and accessory sex glands' blood flow after ejaculation, and if those changes differ according to the process that leads to ejaculation. Twelve adult Corriedale rams were used and assigned at random to the four procedures that lead to ejaculation: (G1) electroejaculation; (G2) artificial vagina; (G3) transrectal ultrasound-guided massage of the accessory sex glands; (G4) natural mating. Hemodynamic characteristics evaluation of the male reproductive system was conducted immediately before and at 30 and 90 min after ejaculation. The internal iliac artery peak systolic velocity (PSV) decreased (P=0.01) and supratesticular artery PSV increased (P=0.042) 90 min after ejaculation in all groups. In conclusion, ejaculation modifies the reproductive system's blood flow, with slight variations depending on the studied ejaculation methods. Additionally, ejaculation altered the internal iliac and supratesticular arteries PSV, and the supratesticular artery end-diastolic velocity (EDV) in rams. The supratesticular artery PSV was the only studied variable that differed according to the procedure that triggered the ejaculation.

Sex life and low back pain: The impact of intradiscal ozone therapy in patients with herniated lumbar disc

STUDY DESIGN

Retrospective cohort study.

OBJECTIVES

To assess the improvement of sexual impairment after percutaneous intradiscal ozone therapy in patients complaining of low back pain (LBP) due to lumbar disc herniation.

METHODS

Between January 2018 and June 2021, 157 consecutive imaging-guided percutaneous intradiscal ozone therapies were performed on 122 patients with LBP and/or sciatic pain due to lumbar disc herniation. Oswestry Disability Index (ODI) was administered before the treatment and at 1-month and 3-month follow-ups and the ODI Section 8 (ODI-8/sex life) values were retrospectively reviewed to evaluate the improvement of sexual impairment and disability.

RESULTS

Mean age of patients was 54.63 ± 12.40. Technical success was achieved in all cases (157/157). Clinical success was registered in 61.97% (88/142) of patients at 1-month follow-up and in 82.69% (116/142) at 3-month follow-up. The mean ODI-8/sex life was 3.73 ± 1.29 before the procedure, 1.71 ± 1.37 at 1-month follow up and 0.44 ± 0.63 at 3-month follow-up. Compared to older patients, subjects under 50 years showed a significantly slower recovery of sexual impairment (p = 0.003). The treated levels were L3-L4, L4-L5, and L5-S1 in 4, 116, and 37 patients, respectively. Patients with L3-L4 disc herniation showed less sexual disability at presentation, with a significantly faster improvement of sexual life (p = 0.03).

CONCLUSIONS

Percutaneous intradiscal ozone therapy is highly effective in reducing sexual impairment due to lumbar disc herniation, and the improvement is faster in older patients and in the case of L3-L4 disc involvement.

Counter culture: causes, extent and solutions of systematic bias in the analysis of behavioural counts

We often quantify the rate at which a behaviour occurs by counting the number of times it occurs within a specific, short observation period. Measuring behaviour in such a way is typically unavoidable but induces error. This error acts to systematically reduce effect sizes, including metrics of particular interest to behavioural and evolutionary ecologists such as R2, repeatability (intra-class correlation, ICC) and heritability. Through introducing a null model, the Poisson process, for modelling the frequency of behaviour, we give a mechanistic explanation of how this problem arises and demonstrate how it makes comparisons between studies and species problematic, because the magnitude of the error depends on how frequently the behaviour has been observed as well as how biologically variable the behaviour is. Importantly, the degree of error is predictable and so can be corrected for. Using the example of parental provisioning rate in birds, we assess the applicability of our null model for modelling the frequency of behaviour. We then survey recent literature and demonstrate that the error is rarely accounted for in current analyses. We highlight the problems that arise from this and provide solutions. We further discuss the biological implications of deviations from our null model, and highlight the new avenues of research that they may provide. Adopting our recommendations into analyses of behavioural counts will improve the accuracy of estimated effect sizes and allow meaningful comparisons to be made between studies.

Sex, ducks, and rock "n" roll: Mathematical model of sexual response

In this paper, we derive and analyze a mathematical model of a sexual response. As a starting point, we discuss two studies that proposed a connection between a sexual response cycle and a cusp catastrophe and explain why that connection is incorrect but suggests an analogy with excitable systems. This then serves as a basis for derivation of a phenomenological mathematical model of a sexual response, in which the variables represent levels of physiological and psychological arousal. Bifurcation analysis is performed to identify stability properties of the model's steady state, and numerical simulations are performed to illustrate different types of behavior that can be observed in the model. Solutions corresponding to the dynamics associated with the Masters-Johnson sexual response cycle are represented by "canard"-like trajectories that follow an unstable slow manifold before making a large excursion in the phase space. We also consider a stochastic version of the model, for which spectrum, variance, and coherence of stochastic oscillations around a deterministically stable steady state are found analytically, and confidence regions are computed. Large deviation theory is used to explore the possibility of stochastic escape from the neighborhood of the deterministically stable steady state, and the methods of an action plot and quasi-potential are employed to compute most probable escape paths. We discuss implications of the results for facilitating better quantitative understanding of the dynamics of a human sexual response and for improving clinical practice.

Exploring Male Multiple Orgasm in a Large Online Sample: Refining Our Understanding

BACKGROUND

The scientific literature on multiple orgasm in males is small. There is little consensus on a definition, and significant controversy about whether multiple orgasm is a unitary experience.

AIMS

This study has 2 goals: (i) describing the experience of male multiple orgasm; (ii) investigating whether there are different profiles of multiple orgasm in men.

METHODS

Data from a culturally diverse online convenience sample of 122 men reporting multiple orgasm were collected. Data reduction analyses were conducted using principal components analysis (PCA) on 13 variables of interest derived from theory and the existing literature. A K-means cluster analysis followed, from which a 4-cluster solution was retained.

RESULTS

While the range of reported orgasms varied from 2 to 30, the majority (79.5%, N = 97) of participants experienced between 2 and 4 orgasms separated by a specific time interval during which further stimulation was required to achieve another orgasm. Most participants reported maintaining their erections throughout and ejaculating with every orgasm. Age was not a significant correlate of the multiple orgasm experience which occurred more frequently in a dyadic context. Four different profiles of multiorgasmic men were described.

STRENGTHS & LIMITATIONS

This study constitutes a rare attempt to collect systematic self-report data concerning the experience of multiple orgasm in a relatively large sample. Limitations include the lack of validated measures, memory bias associated with self-reported data and retrospective designs, the lack of a control group and of physiological measurement.

CONCLUSION

Our study suggests that multiple orgasm in men is not a unitary phenomenon and sets the stage for future self-report and laboratory study. Griffin-Mathieu G, Berry M, Shtarkshall RA, Amsel R, Binik YM, Gérard M. Exploring Male Multiple Orgasm in a Large Online Sample: Refining Our Understanding. J Sex Med 2021;XX:XXX-XXX.

No evidence for prolactin's involvement in the post-ejaculatory refractory period

In many species, ejaculation is followed by a state of decreased sexual activity, the post-ejaculatory refractory period. Several lines of evidence have suggested prolactin, a pituitary hormone released around the time of ejaculation in humans and other animals, to be a decisive player in the establishment of the refractory period. However, data supporting this hypothesis is controversial. We took advantage of two different strains of house mouse, a wild derived and a classical laboratory strain that differ substantially in their sexual performance, to investigate prolactin's involvement in sexual activity and the refractory period. First, we show that there is prolactin release during sexual behavior in male mice. Second, using a pharmacological approach, we show that acute manipulations of prolactin levels, either mimicking the natural release during sexual behavior or inhibiting its occurrence, do not affect sexual activity or shorten the refractory period, respectively. Therefore, we show compelling evidence refuting the idea that prolactin released during copulation is involved in the establishment of the refractory period, a long-standing hypothesis in the field of behavioral endocrinology.

Modeling Human Sexual Motivation in Rodents: Some Caveats

Sexual behavior is activated by motivation. An overwhelming majority of experimental studies of the intricacies of sexual motivation has been performed in rodents, most of them in rats. Sometimes it is desirable to generalize results obtained in this species to other species, particularly the human. It is hoped that studies of the neurobiology of rodent sexual behavior may shed light on the central nervous mechanisms operating in the human, and the search for efficient pharmacological treatments of human sexual dysfunctions relies partly on studies performed in rodents. Then the issue of generalizability of the rodent data to the human becomes crucial. We emphasize the importance of distinguishing between copulatory acts, behavior involving the genitals, and the preceding event, the establishment of physical contact with a potential mate. Comparisons between the structure of copulatory behavior in rats and humans show abysmal differences, but there may be some similarity in the underlying mechanisms. The endocrine control of sex behavior is shortly mentioned, and we also compare the effects of the few drugs known to affect both rodent and human copulatory behavior. The stimuli activating sexual motivation, often called desire in the human literature, are examined, and the sexual approach behaviors in rats and humans are compared. There is a striking similarity between these species in how these behaviors respond to drugs. It is then shown that the intensity of sexual approach is unrelated to the intensity of copulatory behavior. Even though the approach is a requisite for copulation, an activity that requires at least two individuals in close physical contact, these two aspects of sexuality do not covary. This is similar to the role of the testosterone in men and male rats: although the hormone is needed for sex behavior, there is no correlation between serum testosterone concentration and the intensity of copulation. It is also pointed out that human sexual behavior is mostly determined by social conventions, whereas this is not the case in rats and other rodents. It is concluded that some observations in rats can be generalized to the human, but extreme caution must be exercised.

Sadomasochistic erotica and the sexual response cycle: Insights from the Eunuch Archives

The Eunuch Archive (EA) is a website where registered members can post for others to read and rate sexual fantasies that involve genital mutilation and ablation. The EA includes over 8,000 stories. We have previously explored common features of 100 top-rated EA stories. We reasoned that understanding such fantasies may be a step toward recognizing who is at risk of irreversible injury should they act out their fantasies. Here we explore the top-rated EA stories in the context of well-established models for human sexual response. We argue the archetypal storyline from these fantasies, which are characterized by extreme sadomasochism (SM), can be interpreted and understood within the context of these established sexual response models, but we note several ways the fantasies diverge from such models. The stories closely fit the classic Masters and Johnson model, but with a protracted plateau phase resolved with pleasure and pain heightened. Even though the central character in all the stories is a male, the stories align well with the Basson intimacy-based model more characteristic of female motivations to be sexually active. In the fantasies, the central character is willing to sacrifice everything short of his life to develop or strengthen a dyadic relationship. In all the stories, castration is depicted with a sensory intensity equivalent to orgasm. The stories reveal what is both natural and pathological in extreme SM fantasies. They also reveal similarities between female sexual desire and the desire for genital ablation which has not, to the best of our knowledge, been previously elucidated.

Contemporary Vistas in Geriatric Sexuality

There is a substantial increase in the total geriatric population worldwide. This change in demography calls for a greater, deeper, and thorough understanding of elderly and age-related issues. Even though sexuality is a basic and vital driving force, human sexuality, especially elderly sexuality, is frequently misunderstood. Many myths and misconceptions regarding elderly sexuality exist which need attention. Contrary to the popular belief, studies reveal that sexual life continues to be an important aspect in later life and is often viewed by elderly as an expression of love, passion, affection, admiration, and loyalty. Various factors play a role in elderly sexuality including that of bio-psycho-social factors, changes in the body, presence of comorbid conditions along with sexual disorders. Sexual disorders, if present, should be treated and addressed adequately.

No effect of abstinence time on nerve electrophysiological test in premature ejaculation patients

The nerve electrophysiological tests may differentiate the treatment of primary premature ejaculation (PPE) in our previous studies. However, no study verifies if the results will be affected by abstinence time. From January to December in 2016, fifty PPE patients ejaculated within 2 min and 28 control subjects were enrolled. The nerve electrophysiological tests, including dorsal nerve somatosensory evoked potential (DNSEP), glans penis somatosensory evoked potential (GPSEP), and penile sympathetic skin response (PSSR), were recorded before and immediately after ejaculation. The abstinence day was not correlated with the latencies of SEPs or PSSR neither in PE group (P = 0.170, 0.064, and 0.122, respectively) nor in control group (P = 0.996, 0.475, and 0.904, respectively). No statistically differences were found in the latencies of SEPs and PSSR before and after ejaculation in PE patients (P = 0.439, 0.537, and 0.576, respectively) or control subjects (P = 0.102, 0.198, and 0.363, respectively). Thus, abstinence time does not interfere with the nerve electrophysiological test, which is stable in determining the nerve function of PPE patients.

Quantifying the Sexual Afterglow: The Lingering Benefits of Sex and Their Implications for Pair-Bonded Relationships

Sex presumably facilitates pair bonding, but how do partners remain pair-bonded between sexual acts? Evolutionary perspectives suggest that sexual afterglow serves this purpose. We explored how long sexual satisfaction would remain elevated following sex and predicted that stronger sexual afterglow would characterize more satisfying partnerships. We pooled the data from two independent, longitudinal studies of newlywed couples to examine these issues. Spouses reported their daily sexual activity and sexual satisfaction for 14 days and their marital satisfaction at baseline and 4 or 6 months later. Results demonstrated that sexual satisfaction remained elevated approximately 48 hr after sex, and spouses experiencing a stronger afterglow reported higher levels of marital satisfaction both at baseline and over time. We interpret these findings as evidence that sexual afterglow is a proximal cognitive mechanism through which sex promotes pair bonding.

Kisspeptin modulates sexual and emotional brain processing in humans

BACKGROUND. Sex, emotion, and reproduction are fundamental and tightly entwined aspects of human behavior. At a population level in humans, both the desire for sexual stimulation and the desire to bond with a partner are important precursors to reproduction. However, the relationships between these processes are incompletely understood. The limbic brain system has key roles in sexual and emotional behaviors, and is a likely candidate system for the integration of behavior with the hormonal reproductive axis. We investigated the effects of kisspeptin, a recently identified key reproductive hormone, on limbic brain activity and behavior.

METHODS. Using a combination of functional neuroimaging and hormonal and psychometric analyses, we compared the effects of kisspeptin versus vehicle administration in 29 healthy heterosexual young men.

RESULTS. We demonstrated that kisspeptin administration enhanced limbic brain activity specifically in response to sexual and couple-bonding stimuli. Furthermore, kisspeptin’s enhancement of limbic brain structures correlated with psychometric measures of reward, drive, mood, and sexual aversion, providing functional significance. In addition, kisspeptin administration attenuated negative mood.

CONCLUSIONS. Collectively, our data provide evidence of an undescribed role for kisspeptin in integrating sexual and emotional brain processing with reproduction in humans. These results have important implications for our understanding of reproductive biology and are highly relevant to the current pharmacological development of kisspeptin as a potential therapeutic agent for patients with common disorders of reproductive function.

FUNDING. National Institute for Health Research (NIHR), Wellcome Trust (Ref 080268), and the Medical Research Council (MRC).

The whole versus the sum of some of the parts: toward resolving the apparent controversy of clitoral versus vaginal orgasms

BACKGROUND

The nature of a woman's orgasm has been a source of scientific, political, and cultural debate for over a century. Since the Victorian era, the pendulum has swung from the vagina to the clitoris, and to some extent back again, with the current debate stuck over whether internal sensory structures exist in the vagina that could account for orgasms based largely on their stimulation, or whether stimulation of the external glans clitoris is always necessary for orgasm.

METHOD

We review the history of the clitoral versus vaginal orgasm debate as it has evolved with conflicting ideas and data from psychiatry and psychoanalysis, epidemiology, evolutionary theory, feminist political theory, physiology, and finally neuroscience.

RESULTS

A new synthesis is presented that acknowledges the enormous potential women have to experience orgasms from one or more sources of sensory input, including the external clitoral glans, internal region around the "G-spot" that corresponds to the internal clitoral bulbs, the cervix, as well as sensory stimulation of non-genital areas such as the nipples.

CONCLUSIONS

With experience, stimulation of one or all of these triggering zones are integrated into a "whole" set of sensory inputs, movements, body positions, autonomic arousal, and partner- and contextual-related cues, that reliably induces pleasure and orgasm during masturbation and copulation. The process of integration is iterative and can change across the lifespan with new experiences of orgasm.

Do rats have orgasms?

BACKGROUND

Although humans experience orgasms with a degree of statistical regularity, they remain among the most enigmatic of sexual responses; difficult to define and even more difficult to study empirically. The question of whether animals experience orgasms is hampered by similar lack of definition and the additional necessity of making inferences from behavioral responses.

METHOD

Here we define three behavioral criteria, based on dimensions of the subjective experience of human orgasms described by Mah and Binik, to infer orgasm-like responses (OLRs) in other species: 1) physiological criteria that include pelvic floor and anal muscle contractions that stimulate seminal emission and/or ejaculation in the male, or that stimulate uterine and cervical contractions in the female; 2) short-term behavioral changes that reflect immediate awareness of a pleasurable hedonic reward state during copulation; and 3) long-term behavioral changes that depend on the reward state induced by the OLR, including sexual satiety, the strengthening of patterns of sexual arousal and desire in subsequent copulations, and the generation of conditioned place and partner preferences for contextual and partner-related cues associated with the reward state. We then examine whether physiological and behavioral data from observations of male and female rats during copulation, and in sexually-conditioned place- and partner-preference paradigms, are consistent with these criteria.

RESULTS

Both male and female rats display behavioral patterns consistent with OLRs.

CONCLUSIONS

The ability to infer OLRs in rats offers new possibilities to study the phenomenon in neurobiological and molecular detail, and to provide both comparative and translational perspectives that would be useful for both basic and clinical research.

Rethinking Bateman's Principles: Challenging Persistent Myths of Sexually Reluctant Females and Promiscuous Males

In 1948, Angus Bateman published a paper on fruit flies that tested Charles Darwin's ideas of sexual selection. Based on this one fruit fly study, Bateman concluded that because males are able to produce millions of small sperm, males are likely to behave promiscuously, mating with as many females as possible. On the other hand, because females produce relatively fewer, larger, and presumably more expensive eggs, females are likely to be very discriminating in selecting only one high-quality sexual partner. He also posited that a male's reproductive success increases linearly with the number of females he is able to mate with, but that a female's reproductive success peaks after she mates with only one male. Consequently, in almost all organisms, sexual selection acts most strongly on males. These ideas became a recurring theme in attempts to explain wide-ranging differences in male and female behavior not only in nonhuman animals but also in humans. As such, Bateman's conclusions and predictions have become axiomatic and, at times, have gone unquestioned even when modern empirical data do not conform to this model. This article reviews the origins and history of these ideas and uses modern data to highlight the current and growing controversy surrounding the validity and general applicability of this paradigm.

Normal male sexual function: emphasis on orgasm and ejaculation

Orgasm and ejaculation are two separate physiological processes that are sometimes difficult to distinguish. Orgasm is an intense transient peak sensation of intense pleasure creating an altered state of consciousness associated with reported physical changes. Antegrade ejaculation is a complex physiological process that is composed of two phases (emission and expulsion), and is influenced by intricate neurological and hormonal pathways. Despite the many published research projects dealing with the physiology of orgasm and ejaculation, much about this topic is still unknown. Ejaculatory dysfunction is a common disorder, and currently has no definitive cure. Understanding the complex physiology of orgasm and ejaculation allows the development of therapeutic targets for ejaculatory dysfunction. In this article, we summarize the current literature on the physiology of orgasm and ejaculation, starting with a brief description of the anatomy of sex organs and the physiology of erection. Then, we describe the physiology of orgasm and ejaculation detailing the neuronal, neurochemical, and hormonal control of the ejaculation process.

The importance of waiting

Neural circuits that prevent a male C. elegans worm from copulating for several minutes after ejaculation have been identified.

Caenorhabditis elegans male sensory-motor neurons and dopaminergic support cells couple ejaculation and post-ejaculatory behaviors

The circuit structure and function underlying post-coital male behaviors remain poorly understood. Using mutant analysis, laser ablation, optogenetics, and Ca²⁺ imaging, we observed that following C. elegans male copulation, the duration of post-coital lethargy is coupled to cellular events involved in ejaculation. We show that the SPV and SPD spicule-associated sensory neurons and the spicule socket neuronal support cells function with intromission circuit components, including the cholinergic SPC and PCB and the glutamatergic PCA sensory-motor neurons, to coordinate sex muscle contractions with initiation and continuation of sperm movement. Our observations suggest that the SPV and SPD and their associated dopamine-containing socket cells sense the intrauterine environment through cellular endings exposed at the spicule tips and regulate both sperm release into the hermaphrodite and the recovery from post-coital lethargy.

DOI:http://dx.doi.org/10.7554/eLife.02938.001

The nematode worm, C. elegans, is roughly 1 mm long, made up of around 1000 cells and has two sexes: male and hermaphrodite. Hermaphrodite worms produce both eggs and sperm and can self-fertilize to generate around 300 offspring each time. Fertilization by a male, on the other hand, results in three times as many progeny and introduces genetic diversity into the population. However, it also reduces the lifespan of the hermaphrodite.

Mating also incurs a cost for males: it requires a lot of energy, which prevents male works from engaging in other activities, such as feeding, and it also increases their risk of predation. In many species, including C. elegans, the frequency with which a male can mate is limited by a period of reduced mating drive and ability that follows each instance of successful mating. However, the molecular and cellular basis of this ‘refractory period’ remains largely unclear.

Using a range of techniques, LeBoeuf et al. have now identified the circuits that regulate male mating behavior in C. elegans. When male worms were introduced into a Petri dish containing 15 hermaphrodites, most males initiated mating within about 2 min. The length of the refractory period varied between worms, but averaged roughly 12 min. This consisted of a period of disinterest, in which males did not approach hermaphrodites, followed by a period in which males attempted mating but were slower and less efficient, suggesting that the neural circuits controlling mating behaviors had yet to recover completely.

Males with longer refractory periods produced more progeny in their second mating than those with shorter refractory periods, suggesting that the interval also enables males to replenish their sperm levels. Further experiments revealed that a chemical transmitter called dopamine promotes ejaculation and then immediately reduces the worm's activity levels, giving rise to the refractory period.

By enforcing a delay between matings, the refractory period may also increase the likelihood that successive matings will be with different hermaphrodites, helping to maximize the number and diversity of offspring. Some aspects of the neural circuitry that controls the refractory period in C. elegans resemble those seen in mammals, suggesting that insights gained from an animal with 1000 cells could also be relevant to more complex species.

DOI:http://dx.doi.org/10.7554/eLife.02938.002

The pharmacology of the human female orgasm - its biological and physiological backgrounds

The female orgasm has been examined over the years by numerous scientific disciplines yet it still has many secrets to be disclosed. Because its physiology, especially its neurophysiology, is sparingly understood its pharmacology is necessarily limited based mainly on the side effects of drugs. Few published studies have used a placebo group as controls. The paucity of focussed studies is well illustrated by the fact that there still is no approved medication to treat female orgasmic dysfunction. The present brief overview examines the most important aspects of its biology and especially its physiology highlighting the many questions that need answering if we are to have a comprehensive pharmacology of the female orgasm.

Gender similarities and differences in sexual arousal, desire, and orgasmic pleasure in the laboratory

Relatively little is known about gender differences in the orgasm experience. The objectives of this study were to compare men's and women's patterns of sexual arousal and desire before and after orgasm, and the predictors of their orgasmic pleasure. Using their typical technique, where masturbation enjoyment was similar to that experienced at home, 38 men and 38 women masturbated to orgasm in the laboratory. Physiological sexual arousal (genital temperature) and subjective sexual arousal and desire measurements were taken at baseline, after masturbation almost to orgasm, and immediately and 15 minutes after orgasm. In both genders, all measures increased significantly during masturbation, with a greater buildup leading to a more pleasurable orgasm. After orgasm, however, sexual arousal and desire decreased more quickly and consistently in men than in women, thereby replicating Masters and Johnson's (1966) observations. More men than women exhibited resolution of subjective sexual arousal and sexual satiation; their genital temperature also decreased more than women's but did not return to baseline. Women's orgasmic pleasure was related to a postorgasmic decrease in genital temperature but, unexpectedly, the maintenance of subjective sexual arousal and desire. Future studies should explore whether this pattern explains gender differences in the pursuit of additional orgasms.

Evolving ideas about the male refractory period

The male refractory period (MRP) continues to be a topic of discussion and debate within the field of sexual medicine. To date explanations rely on central descending (efferent) influences involving specific neurotransmitter systems. Herein we explore the issue of the male refractory period, identifying problems with current explanations, specifying the parameters of an adequate model, and suggesting possible mechanisms mediating this phenomenon. We review the literature regarding existing explanations for the MRP and look to other systems of physiological regulation that might provide a model for the conceptualization of the MRP. Our approach differs from traditional explanations in that it emphasizes the possible roles of various peripheral, rather than central, feedback (afferent) systems that affect peripheral autonomic functioning and response. Yet our approach is consistent with other peripheral regulatory feedback systems controlling autonomic response related to such processes as heart rate, respiration, and gut motility. Although direct empirical research supporting our approach is lacking, sufficient evidence exists to support the idea that such processes are not only possible but likely with respect to the male refractory period. We suggest several lines of research that might provide empirical support for this approach.

The human sexual response cycle: brain imaging evidence linking sex to other pleasures

Sexual behavior is critical to species survival, yet comparatively little is known about the neural mechanisms in the human brain. Here we systematically review the existing human brain imaging literature on sexual behavior and show that the functional neuroanatomy of sexual behavior is comparable to that involved in processing other rewarding stimuli. Sexual behavior clearly follows the established principles and phases for wanting, liking and satiety involved in the pleasure cycle of other rewards. The studies have uncovered the brain networks involved in sexual wanting or motivation/anticipation, as well as sexual liking or arousal/consummation, while there is very little data on sexual satiety or post-orgasmic refractory period. Human sexual behavior also interacts with other pleasures, most notably social interaction and high arousal states. We discuss the changes in the underlying brain networks supporting sexual behavior in the context of the pleasure cycle, the changes to this cycle over the individual's life-time and the interactions between them. Overall, it is clear from the data that the functional neuroanatomy of sex is very similar to that of other pleasures and that it is unlikely that there is anything special about the brain mechanisms and networks underlying sex.