Penile sensitivity in men: a composite of recent findings

Male delayed orgasm and anorgasmia: a practical guide for sexual medicine providers

Delayed orgasm (DO) is defined as increased latency of orgasm despite adequate sexual stimulation and desire. Anorgasmia (AO) is characterized as the absence of orgasm. Etiologies of DO/AO include medication-induced, psychogenic, endocrine, and genitopelvic dysesthesia. Given the multifactorial complex nature of this disorder, a thorough history and physical examination represent the most critical components of patient evaluation in the clinical setting. Treating DO/AO can be challenging due to the lack of standardized FDA-approved pharmacotherapies. There is no standardized treatment plan for DO/AO, though common treatments plans are often multidisciplinary and may include adjustment of offending medications and sex therapy. In this review, we summarize the etiology, diagnosis, and treatment of DO/AO.

Neurons for Ejaculation and Factors Affecting Ejaculation

Simple Summary

Sexual dysfunctions are rarely discussed in our current society. Males experience different sexual dysfunctions, including erectile, infertility, and ejaculatory dysfunctions. In this review only the ejaculatory dysfunction will be discussed. Ejaculation is defined as the ejection of contents collectively from the vas deferens, seminal vesicle, prostate and Cowper’s glands. It is completely controlled by a population of neurons present in the lumbar spinal cord. The presence of lesion in these neurons ceases the ejaculatory behavior in males. This population of neurons was first identified in rats; however, recently it was confirmed that these neurons are present in human males as well. The issues are known as ejaculatory dysfunction. The following are the different types of ejaculatory dysfunctions: early ejaculation, ejaculation into the urinary bladder, late ejaculation and no ejaculation.

Abstract

Ejaculation is a reflex and the last stage of intercourse in male mammals. It consists of two coordinated phases, emission and expulsion. The emission phase consists of secretions from the vas deferens, seminal vesicle, prostate, and Cowper’s gland. Once these contents reach the posterior urethra, movement of the contents becomes inevitable, followed by the expulsion phase. The urogenital organs are synchronized during this complete event. The L3–L4 (lumbar) segment, the spinal cord region responsible for ejaculation, nerve cell bodies, also called lumbar spinothalamic (LSt) cells, which are denoted as spinal ejaculation generators or lumbar spinothalamic cells [Lst]. Lst cells activation causes ejaculation. These Lst cells coordinate with [autonomic] parasympathetic and sympathetic assistance in ejaculation. The presence of a spinal ejaculatory generator has recently been confirmed in humans. Different types of ejaculatory dysfunction in humans include premature ejaculation (PE), retrograde ejaculation (RE), delayed ejaculation (DE), and anejaculation (AE). The most common form of ejaculatory dysfunction studied is premature ejaculation. The least common forms of ejaculation studied are delayed ejaculation and anejaculation. Despite the confirmation of Lst in humans, there is insufficient research on animals mimicking human ejaculatory dysfunction.

The Lost Penis Syndrome: A New Clinical Entity in Sexual Medicine

INTRODUCTION

The "lost penis syndrome" (LPS) is a term often used in non-clinical settings to describe the subjective perception of the loss of cutaneous and proprioceptive feelings of the male organ during vaginal penetration. Although deserving clinical attention, this syndrome did not receive any consideration in the medical literature. Notwithstanding, it represents a relatively unexceptional condition among patients in sexual medicine clinics, and it is often reported together with other sexual dysfunctions, especially delayed ejaculation, anejaculation, male anorgasmia and inability to maintain a full erection.

OBJECTIVES

To draft a new conceptual characterization of the LPS, defined as a lack of penile somesthetic sensations during sexual penetration due to various causes and leading to several sexual consequences in both partners.

METHODS

Based on an extensive literature review and physiological assumptions, the mechanisms contributing to friction during penovaginal intercourse, and their correlation to LPS, have been explored, as well as other nonanatomical factors possibly contributing to the loss of penile sensations.

RESULTS

Efficient penile erection and sensitivity, optimal vaginal lubrication and trophism contribute to penovaginal friction. Whenever one of these processes does not occur, loss of penile sensation defined as LPS can occur. Sociocultural, psychopathological and age-related (ie, couplepause) factors are also implicated in the etiology. Four types of LPS emerged from the literature review: anatomical and/or functional, behavioral, psychopathological and iatrogenic. According to the subtype, a wide variety of treatments can be employed, including PDE5i, testosterone replacement therapy and vaginal cosmetic surgery, as well as targeted therapy for concomitant sexual comorbidity.

CONCLUSION

We held up the mirror on LPS as a clinically existing multifactorial entity and provided medical features and hypotheses contributing to or causing the occurrence of LPS. In the light of a sociocultural and scientific perspective, we proposed a description and categorization of this syndrome hypothesizing its usefulness in daily clinical practice. Colonnello E, Limoncin E, Ciocca G, et al. The Lost Penis Syndrome: A New Clinical Entity in Sexual Medicine. Sex Med Rev 2021;XX:XXX-XXX.

Small fibre pathology is associated with erectile dysfunction in men with type 2 diabetes

AIMS

The aim of this study was to evaluate the contribution of small and large fibre neuropathy to erectile dysfunction (ED) in men with type 2 diabetes (T2D).

METHODS

Measures of small and large fibre neuropathy were evaluated in 49 participants with T2D and 20 age-matched controls.

RESULTS

ED was present in 59% of participants with T2D. There was no difference in age, duration of diabetes, blood pressure, lipid profile, vibration perception threshold (V) (14.3 ± 7.8 vs 11.2 ± 6.6, P = .429), peroneal (41.4 ± 8.2 vs 44.8 ± 4.4, P = .10) and sural (45.4 ± 5.6 vs 47.1 ± 5.8) nerve conduction velocities (m/s), cold (25.1 ± 3.8 vs 26.2 ± 2.9, P = .815) and warm (43.2 ± 4.0 vs 41.0 ± 3.8) perception thresholds (°C), and deep breathing heart rate variability (18 ± 8 vs 18 ± 8) between participants with and without ED. However, intraepidermal nerve fibre density (no./mm² ) (4.6 ± 2.8 vs 13.7 ± 2.7, P < .001), corneal nerve fibre density (no./mm² ) (23.5 ± 6.8 vs 31.3 ± 8.2, P < .001), corneal nerve fibre branch density (no./mm² ) (55.4 ± 35.3 vs 97.7 ± 46.4, P = .004), corneal nerve fibre length (mm/mm² ) (17.6 ± 6.8 vs 27.3 ± 6.8, P < .001), and sural (7.7 ± 6.1 vs 14.6 ± 6.7, P = .003) and peroneal (2.5 ± 2.0 vs 4.7 ± 2.0, P = .003) nerve amplitudes were significantly lower in participants with ED compared with those without ED.

CONCLUSION

ED affects almost 2/3 of men with T2D and is associated with small nerve fibre damage but preserved nerve conduction and cardiac autonomic function. Corneal confocal microscopy may serve as a useful non-invasive imaging method to identify small fibre damage in patients with T2D and ED.

Neural Basis of Touch and Proprioception in Primate Cortex

The sense of proprioception allows us to keep track of our limb posture and movements and the sense of touch provides us with information about objects with which we come into contact. In both senses, mechanoreceptors convert the deformation of tissues-skin, muscles, tendons, ligaments, or joints-into neural signals. Tactile and proprioceptive signals are then relayed by the peripheral nerves to the central nervous system, where they are processed to give rise to percepts of objects and of the state of our body. In this review, we first examine briefly the receptors that mediate touch and proprioception, their associated nerve fibers, and pathways they follow to the cerebral cortex. We then provide an overview of the different cortical areas that process tactile and proprioceptive information. Next, we discuss how various features of objects-their shape, motion, and texture, for example-are encoded in the various cortical fields, and the susceptibility of these neural codes to attention and other forms of higher-order modulation. Finally, we summarize recent efforts to restore the senses of touch and proprioception by electrically stimulating somatosensory cortex. © 2018 American Physiological Society. Compr Physiol 8:1575-1602, 2018.

Delayed Ejaculation: Pathophysiology, Diagnosis, and Treatment

Delayed ejaculation (DE) is a poorly defined and uncommon form of male sexual dysfunction, characterized by a marked delay in ejaculation or an inability to achieve ejaculation. It is often quite concerning to patients and their partners, and sometimes frustrates couples' attempts to conceive. This article aims to review the pathophysiology of DE and anejaculation (AE), to explore our current understanding of the diagnosis, and to present the treatment options for this condition. Electronic databases were searched from 1966 to October 2017, including PubMed (MEDLINE) and Embase. We combined “delayed ejaculation,” “retarded ejaculation,” “inhibited ejaculation,” or “anejaculation” as Medical Subject Headings (MeSH) terms or keywords with “epidemiology,” “etiology,” “pathophysiology,” “clinical assessment,” “diagnosis,” or “treatment.” Relevant sexual medicine textbooks were searched as well. The literature suggests that the pathophysiology of DE/AE is multifactorial, including both organic and psychosocial factors. Despite the many publications on this condition, the exact pathogenesis is not yet known. There is currently no single gold standard for diagnosing DE/AE, as operationalized criteria do not exist. The history is the key to the diagnosis. Treatment should be cause-specific. There are many approaches to treatment planning, including various psychological interventions, pharmacotherapy, and specific treatments for infertile men. An approved form of drug therapy does not exist. A number of approaches can be employed for infertile men, including the collection of nocturnal emissions, prostatic massage, prostatic urethra catheterization, penile vibratory stimulation, probe electroejaculation, sperm retrieval by aspiration from either the vas deferens or the epididymis, and testicular sperm extraction.

The pathophysiology of delayed ejaculation

Delayed ejaculation (DE) is probably least studied, and least understood of male sexual dysfunctions, with an estimated prevalence of 1–4% of the male population. Pathophysiology of DE is multifactorial and including psychosexual-behavioral and cultural factors, disruption of ejaculatory apparatus, central and peripheral neurotransmitters, hormonal or neurochemical ejaculatory control and psychosocial factors. Although knowledge of the physiology of the DE has increased in the last two decade, our understanding of the different pathophysiological process of the causes of DE remains limited. To provide a systematic update on the pathophysiology of DE. A systematic review of Medline and PubMed for relevant publications on ejaculatory dysfunction (EjD), DE, retarded ejaculation, inhibited ejaculation, and climax was performed. The search was limited to the articles published between the January 1960 and December 2015 in English. Of 178 articles, 105 were selected for this review. Only those publications relevant to the pathophysiology, epidemiology and prevalence of DE were included. The pathophysiology of DE involves cerebral sensory areas, motor centers, and several spinal nuclei that are tightly interconnected. The biogenic, psychogenic and other factors strongly affect the pathophysiology of DE. Despite the many publications on this disorder, there still is a paucity of publications dedicated to the subject.

Delayed orgasm and anorgasmia

Delayed orgasm/anorgasmia defined as the persistent or recurrent difficulty, delay in, or absence of attaining orgasm after sufficient sexual stimulation, which causes personal distress. Delayed orgasm and anorgasmia are associated with significant sexual dissatisfaction. A focused medical history can shed light on the potential etiologies, which include medications, penile sensation loss, endocrinopathies, penile hyperstimulation, and psychological etiologies. Unfortunately, there are no excellent pharmacotherapies for delayed orgasm/anorgasmia, and treatment revolves largely around addressing potential causative factors and psychotherapy.

Effect of the aqueous extract of the aerial parts of Monsonia angustifolia E. Mey. Ex A. Rich., on the sexual behaviour of male Wistar rats

Background

Monsonia angustifolia (Geraniaceae) is a medicinal plant traditionally used in South Africa to increase libido and to treat erectile dysfunction.

Methods

In-vivo aphrodisiac activities of the crude extracts of the plant prepared in water at 3, 30 and 300 mg/kg body weight were evaluated for 7 days using sildenafil citrate (Viagra) and 1 % ethanol in distilled water as positive and negative controls respectively. Male rats were selected and monitored in each group for sexual behaviour by exposing them to sexually receptive females on days 1, 3 and 7 for 60 minutes each between 7:00 pm and 3:00 am. The following male sexual parameters were observed: Mount Frequency (MF), Intromission Frequency (IF), Mount Latency (ML), Intromission Latency (IL), Ejaculation Frequency (EF), Ejaculatory Latency (EL) and Post-Ejaculatory Interval (PEI).

Results

The administration of the extract resulted in significant increase (p < 0.05) in mount frequency, intromission frequency, ejaculation frequency, ejaculation latency and serum hormone concentrations. The computed indices of sexual behaviour such as erection, quick flips, long flips and total penile reflexes were also increased. However, the mount latency, intromission latency and post ejaculation interval were significantly decreased throughout the experimental period. The administration of 300 mg/kg body weight of the aqueous extract produced the best effects in all the parameters.

Conclusion

Generally, the extract of Monsonia angustifolia produced pro-sexual stimulatory effects in the male rats especially when administered at 300 mg/kg body weight. The results validate the use of the plant by the indigenous people to increase libido and treat premature ejaculation and erectile dysfunction in males.

Histological Correlates of Penile Sexual Sensation: Does Circumcision Make a Difference?

INTRODUCTION

The question of whether removal of sensory receptors in the prepuce by circumcision affects sensitivity and/or sexual pleasure is often debated.

AIMS

To examine histological correlates relevant to penile sensitivity and sexual pleasure.

METHODS

Systematic review of the scientific literature on penile structures that might affect sensitivity and sexual sensation. Articles were included if they contained original data on human male penile histology or anatomy. Individual articles, including reference lists, were evaluated. They were then considered in relation to physiological data from articles retrieved by a previous systematic review.

RESULTS

We retrieved 41 publications on penile structure. Considered in the light of 12 reporting physiological measurements, our evaluation finds that sexual response is unlikely to involve Meissner's corpuscles, whose density in the prepuce diminishes at the time of life when male sexual activity is increasing. Free nerve endings also show no correlation with sexual response. Because tactile sensitivity of the glans decreases with sexual arousal, it is unrelated to sexual sensation. Thermal sensitivity seems part of the reward mechanism of intercourse. Vibrational sensitivity is not related to circumcision status. Observations that penile sexual sensation is higher post circumcision are consistent with greater access of genital corpuscles to sexual stimuli after removal of the prepuce. This is based on the distribution of these corpuscles (which are located in the glans) and, in uncircumcised men, the position of the retracted prepuce during intercourse, rather than any change in the number of genital corpuscles. The scientific literature suggests that any sexual effect of circumcised men may depend solely on exposure of the glans and not on the absence of the prepuce.

CONCLUSION

Based on histological findings and correlates of sexual function, loss of the prepuce by circumcision would appear to have no adverse effect on sexual pleasure. Our evaluation supports overall findings from physiological measurements and survey data.

Sexuality in advanced age in Jewish thought and law

Judaism has a positive attitude to sexual relations within a marriage, and views such sexual relations as important not only for procreation but also as part of the framework of marriage. This is true for any age group, and sexuality is seen as an essential element of marriage for couples of advanced age. In this article, the authors present the views of Jewish law and thought regarding sexuality among older couples. The authors illustrate this using 3 case studies of couples who sought guidance in the area of sexuality. In addition, this area of counseling benefits greatly from an ongoing relationship and dialogue between expert rabbis in the field and therapists treating older Orthodox Jewish patients for sexual dysfunction. The triad relationship of couple, therapist, and rabbi enhances the ability to treat and assist such couples to seek treatment and overcome their difficulties.

The effect of condoms on penile vibrotactile sensitivity thresholds in young, heterosexual men

INTRODUCTION

Investigating the ways in which barrier methods such as condoms may affect penile sensory thresholds has potential relevance to the development of interventions in men who experience negative effects of condoms on sexual response and sensation. A quantitative, psychophysiological investigation examining the degree to which sensations are altered by condoms has, to date, not been conducted.

AIM

The objective of this study was to examine penile vibrotactile sensitivity thresholds in both flaccid and erect penises with and without a condom while comparing men who do and those who do not report condom-associated erection problems (CAEP).

METHODS

Penile vibrotactile sensitivity thresholds were assessed among a total of 141 young, heterosexual men using biothesiometry. An incremental two-step staircase method was used and repeated three times for each of four conditions. Intra-class correlation coefficients (ICCs) were calculated for all vibratory assessments. Penile vibratory thresholds were compared using a mixed-model analysis of variance.

MAIN OUTCOME MEASURES

Penile vibrotactile sensitivity thresholds with and without a condom, erectile function measured by International Index of Erectile Function Questionnaire, and self-reported degree of erection.

RESULTS

Significant main effects of condoms (yes/no) and erection (yes/no) were found. No main or interaction effects of CAEP were found. Condoms were associated with higher penile vibrotactile sensitivity thresholds (F[1,124] = 17.11, P < 0.001). Penile vibrotactile thresholds were higher with an erect penis than with a flaccid penis (F[1,124] = 4.21, P = 0.042).

CONCLUSION

The current study demonstrates the feasibility of measuring penile vibratory thresholds with and without a condom in both erect and flaccid experimental conditions. As might be expected, condoms increased penile vibrotactile sensitivity thresholds. Interestingly, erections were associated with the highest thresholds. Thus, this study was the first to document that erect penises are less sensitive to vibrotactile stimulation than flaccid penises.

Sex for fun: a synthesis of human and animal neurobiology

Sex is a fundamental pleasure, and crucial to the survival of our species. Though not many people would disagree with the proposition that sexual behaviour depends on the brain, the neuroscientific study of human sex is still relatively taboo and much remains to be discovered. On the contrary, excellent experimental animal models (mostly rat) are available that have uncovered major behavioural, neurochemical, and neuroanatomical characteristics of sexual behaviour. Restructuring sexual behaviour into broader terms reflecting behavioural states (wanting, liking, and inhibition) facilitates species comparison, revealing many similarities between animal and human sexual pleasure cycles, some of which can serve as potential avenues of new human sex research. In particular, behavioural and brain evidence clearly shows that motivational and consummatory phases are fundamentally distinct, and that genitally-induced sexual reward is a major factor in sexual learning mechanisms.

Quality of life issues in men undergoing androgen deprivation therapy: a review

Androgen deprivation therapy (ADT) has been an essential treatment option for treating prostate cancer (PCa). The role for hormonal treatment initially was restricted to men with metastatic and inoperable, locally advanced disease. Now it has been extended to neoadjuvant or adjuvant therapy for surgery and radiotherapy, for biochemical relapse after surgery or radiation, and even as primary therapy for non-metastatic disease. Fifty percent of PCa patients treated will receive ADT at some point. There is growing concern about the adverse effects and costs associated with more widespread ADT use. The adverse effects on quality of life (QoL), including physical, social and psychological well-being when men are androgen-deprived, may be considerable. This review examines the QoL issues in the following areas: body feminisation, sexual changes, relationship changes, cognitive and affective symptoms, fatigue, sleep disturbance, depression and physical effects. Further suggestions for therapeutic approaches to reduce these alterations are suggested.

Considerations for a better definition of male orgasmic disorder in DSM V

INTRODUCTION

All of the Diagnostic and Statistical Manual of Mental Disorders, 4th Ed., text revision (DSM-IV-TR) criteria for sexual disorders have been criticized on multiple grounds, including that the criteria lack precision, that the requirement of marked distress is inappropriate, and that the specification of etiological subtypes should be deleted.

AIM

The goal of this article is to review evidence relevant to diagnostic criteria for male orgasmic disorder published since 1990.

METHODS

Medline searches from 1990 forward were conducted using the terms male orgasmic disorder, anorgasmia, delayed ejaculation, retarded ejaculation, ejaculatory delay, and ejaculatory disorder. Early drafts of proposed alterations in diagnostic criteria were submitted to advisors.

MAIN OUTCOME MEASURE

Evidence reviewed was judged by current usage of terminology, evidence allowing precise definition of the syndrome, and evidence concerning separation of the syndrome from distress.

RESULTS

The literature search indicated minimal use of the term male orgasmic disorder and minimal knowledge concerning psychogenic ejaculatory problems.

CONCLUSIONS

It is recommended that the term male orgasmic disorder be replaced with the term delayed ejaculation. Duration and severity criteria are recommended. Since many ejaculatory problems are idiopathic, it is recommended that the etiological subtypes due to psychological or due to combined factors be eliminated.

ORIGINAL RESEARCH—WOMEN’S SEXUAL HEALTH: Physiological Changes in Female Genital Sensation During Sexual Stimulation

INTRODUCTION

A normal sexual response in the female depends on the integrity of afferent sensory input from the genital region. So far genital sensation has been investigated only during a non-excitatory state, and the sensory physiological changes, which occur during the sexual cycle in this region, are still obscured.

AIM

To investigate the sensory status of the female genital region during sexual arousal and orgasm.

MAIN OUTCOME MEASURES

Genital sensory thresholds measured by Quantitative Sensory Testing (vibratory and thermal) were compared in a non-excitatory vs. excitatory state in normal sexually functioning females.

METHODS

Eleven healthy female volunteers were recruited and attended three separate visits. During each session only one anatomical site, either clitoris or vagina was tested for either vibratory or thermal stimuli. A psychophysical method of limits was employed for threshold determination of warm or vibratory stimuli. In each session, all women were tested at baseline, immediately after arousal, after orgasm and three more measurements - 5, 10, and 20 minutes during the recovery state.

RESULTS

A significant decrease in clitoral vibratory sensation threshold was observed between the baseline and the arousal phases (P = 0.003). Comparison of vibratory sensation between baseline and following orgasm at the clitoral and vaginal region showed a significant difference (P < 0.001) for both regions. These changes were not significant for thermal threshold sensation at the clitoral region (P = 0.6).

CONCLUSIONS

This is the first time that genital sensation has been measured during the excitatory phase of the female sexual cycle. This normative data may serve as a baseline for further investigations of the sensory input of the genital organs during intercourse in pathological states.

Ejaculation latency times and their relationship to penile sensitivity in men with normal sexual function

PURPOSE

There is a need for objective and validated measurements of ejaculation latency time and penile sensitivity in men with normal sexual function. We determined 1) the normal range and repeatability of ELT in a laboratory vs at home masturbation and intercourse in normal men, 2) the threshold and repeatability of penile sensitivity on 6 penile surface areas measured by 2 vibrometers and 3) whether penile sensitivity correlates with ejaculation latency time.

MATERIALS AND METHODS

A total of 58 healthy volunteers between 20 and 40 years old provided ejaculation latency times during 3 procedures and were evaluated with a biothesiometer and SMV-5 vibrometer (Suzuki-Matsuoka, Teknologue, Tokyo, Japan) on 6 penile surface areas.

RESULTS

Ejaculation latency time was highest during intercourse (median 8.25 minutes, range 1.32 to 18.31), lower in the laboratory (median 7.22, range 1.37 to 18.79) and lowest during masturbation (median 4.89, range 1.08 to 14.19). The 3 ELT scores were highly reproducible within subjects (ICC 0.88 to 0.93). There was high variability among subjects. Vibrotactile thresholds on 6 penile surface areas were also similar and highly repeatable for the 2 vibrometers (ICC 0.81 to 0.96). However, there was no correlation between penile sensitivity and ELT (R2 less than 8%).

CONCLUSIONS

ELT in the laboratory is lower than during intercourse and higher than during masturbation. Vibrometers produce reliable and repeatable penile vibrotactile threshold results. However, penile sensitivity measurements do not correlate with ELT in men with normal sexual function.

Retarded ejaculation

Retarded ejaculation (RE) has a relatively low prevalence (<3%), yet this condition results in considerable distress, anxiety, and lack of sexual confidence for those suffering from it. Furthermore, men with partners often experience impairment of both the sexual and nonsexual aspects of their relationships, with such negative effects compounded when procreation is a consideration. The definition of RE is ambiguous, due to the variability and paucity of data regarding normal coital ejaculatory latency. RE is influenced by both biogenic and psychogenic components, which may vary over time both between and within individuals. While specific pathophysiology can often be identified, further elucidation of the biogenic components of this dysfunction will require greater understanding of the physiological mechanisms underlying ejaculation. Yet, the most useful strategies for understanding RE will integrate rather than isolate the various biogenic and psychogenic aspects of this dysfunction. Evidence based evaluation and treatment protocols for this disorder are lower than for other sexual dysfunctions, but reports suggest better treatment efficacy when the etiology is predominantly psychogenic. As with erectile dysfunction (ED) and premature ejaculation (PE), if safe and efficacious oral pharmaceuticals are eventually developed for this condition, the treatment algorithm is likely to undergo significant alteration. Even then, however, the most effective treatments are likely to result from a combination treatment that integrates sex coaching with pharmacotherapy.

Psychopharmacology of male rat sexual behavior: modeling human sexual dysfunctions?

Most of our current understanding of the neurobiology, neuroanatomy and psychopharmacology of sexual behavior and ejaculatory function has been derived from preclinical studies in the rat. When a large population of male rats is tested on sexual activity during a number of successive tests, over time individual rats display a very stable sexual behavior that is either slow, normal or fast as characterized by the number of ejaculations performed. These sexual endophenotypes are postulated as rat counterparts of premature (fast rats) or retarded ejaculation (slow rats). Psychopharmacology in these endophenotypes helps to delineate the underlying mechanisms and pathology. This is illustrated by the effects of serotonergic antidepressants and serotonergic compounds on sexual and ejaculatory behavior of rats. These preclinical studies and models contribute to a better understanding of the neurobiology of ejaculation and boost the development of novel drug targets to treat ejaculatory disorders such as premature and retarded ejaculation.

Individual differences in male rat ejaculatory behaviour: searching for models to study ejaculation disorders

In addition to investigating sexual function in rats that display normal ejaculatory behaviour, studying rats that are either 'hyposexual' or 'hypersexual' may provide important insights into the aetiology of ejaculatory dysfunctions in men, such as premature and retarded ejaculation. To this end, rats were matched into groups of 'sluggish', 'normal' and 'rapid' ejaculators based on their ejaculation frequencies displayed in a series of weekly sexual behaviour tests. Selecting rats on this parameter revealed large and stable differences in other parameters of sexual behaviour as well, including ejaculation latency and mount frequency but not intromission frequency and mount latency, putative indices of sexual motivation. Neuroanatomically, Fos immunoreactivity as a measure of neuronal activation was increased in rapid ejaculators compared with sluggish ejaculators in ejaculation-related brain areas, presumably associated with the differences in ejaculatory behaviour. Although the total number of oxytocin neurones within subregions of the hypothalamus did not differ between groups, in the supraoptic nucleus of the hypothalamus more oxytocin neurones were activated in rapid ejaculators compared with the other groups. Apart from the differences observed in ejaculatory behaviour, groups did not differ with respect to their locomotor activity and approach-avoidance behaviour as measured in the elevated plus-maze. Finally, apomorphine-induced stereotypy was similar in sluggish and rapid ejaculators, suggesting no large differences in dopamine susceptibility. Altogether, the present results suggest stable differences in male rat ejaculatory behaviour. Further exploring the neurobiological mechanisms underlying these differences may be a promising approach to gain insights into the aetiology of sexual dysfunctions such as premature, retarded or an-ejaculation.

Animal models of premature and retarded ejaculation

Most of our current understanding of the neurobiology of sexual behavior and ejaculatory function has been derived from animal studies using rats with normal sexual behaviour. However, none of these proposed models adequately represents human ejaculatory disorders. Based on the "ejaculation distribution theory", which postulates that the intravaginal ejaculation latency time in men is represented by a biological continuum, we have developed an animal model for the research of premature and delayed ejaculation. In this model, a large number of male Wistar rats are investigated during 4-6 weekly sexual behavioural tests. Based on the number of ejaculations during 30 min tests, rapid and sluggish ejaculating rats are distinguished, each representing approximately 10% at both ends of a Gaussian distribution. Together with other parameters, such as ejaculation latency time, these rats at either side of the spectrum resemble men with premature and delayed ejaculation, respectively. Comparable to the human situation, in a normal population of rats, endophenotypes exist with regard to basal sexual (ejaculatory) performance.

Tactile sensitivity in women with sexual arousal disorder

Evidence suggests that tactile sensitivity may differ between women with sexual arousal difficulties and women with normal sexual functioning. Tactile sensitivity was examined on the distal portion of the dominant hand index finger and on the lower lip in women with female sexual arousal disorder (FSAD) (n = 17) and in normally functioning women (n = 17). The two groups did not differ significantly in age, length of current relationship or on measures of sexual experience and sexual desire. Hierarchical binary logistic regression indicated that finger threshold was significantly associated with FSAD women versus control women, and hierarchical linear regression indicated that finger threshold was associated with severity of arousal dysfunction. Logistic regression showed that 76.5% of participants were correctly classified and 23.5% were incorrectly classified using tactile sensation as a predictor variable. Possible underlying mechanisms and clinical implications are discussed.

Relevance of an evidence-based ejaculation time cutoff point for neurobiological research of premature ejaculation

The Diagnostic and Statistical Manual (DSM)-IV definition of premature ejaculation is not based on evidence-based studies. In particular, the absence of a well-defined quantitative measure of the intravaginal ejaculation latency time (IELT) makes the DSM definition inadequate. Therefore, the DSM-IV definition should be replaced by a medical definition that incorporates both quantitative as qualitative parameters of premature ejaculation. An evidence-based medical definition should include a cutoff point of the IELT at the 0.5 and 2.5 percentiles of the IELT distribution in the general male population. Such a definition has recently been proposed on the basis of a stopwatch study of the IELT in 491 men from five different countries. Similarly, a cutoff point of ejaculation frequency in laboratory rats enhances the probability to distinguish genuine rapid-ejaculator rats. Only by the strict application of these cutoff points is the probability enhanced that human and animal neurobiological research can prove whether these sexual endophenotypes differ in brain activation, have particular genetic genotypes (polymorphisms), are strictly under genetic control, or are dependent on environmental conditions and/or genotypic/environmental interactions.

Quantitative somatosensory testing of the penis: optimizing the clinical neurological examination

PURPOSE

Quantitative somatosensory testing, including vibration, pressure, spatial perception and thermal thresholds of the penis, has demonstrated neuropathy in patients with a history of erectile dysfunction of all etiologies. We evaluated which measurement of neurological function of the penis was best at predicting erectile dysfunction and examined the impact of location on the penis for quantitative somatosensory testing measurements.

MATERIALS AND METHODS

A total of 107 patients were evaluated. All patients were required to complete the erectile function domain of the International Index of Erectile Function (IIEF) questionnaire, of whom 24 had no complaints of erectile dysfunction and scored within the "normal" range on the IIEF. Patients were subsequently tested on ventral middle penile shaft, proximal dorsal midline penile shaft and glans penis (with foreskin retracted) for vibration, pressure, spatial perception, and warm and cold thermal thresholds.

RESULTS

Mixed models repeated measures analysis of variance controlling for age, diabetes and hypertension revealed that method of measurement (quantitative somatosensory testing) was predictive of IIEF score (F = 209, df = 4,1315, p <0.001), while site of measurement on the penis was not. To determine the best method of measurement, we used hierarchical regression, which revealed that warm temperature was the best predictor of erectile dysfunction with pseudo R(2) = 0.19, p <0.0007. There was no significant improvement in predicting erectile dysfunction when another test was added. Using 37C and greater as the warm thermal threshold yielded a sensitivity of 88.5%, specificity 70.0% and positive predictive value 85.5%.

CONCLUSIONS

Quantitative somatosensory testing using warm thermal threshold measurements taken at the glans penis can be used alone to assess the neurological status of the penis. Warm thermal thresholds alone offer a quick, noninvasive accurate method of evaluating penile neuropathy in an office setting.

The neuropathy of erectile dysfunction

These studies were intended to explore the relationship between autonomic neuropathy and erectile dysfunction (ED). Sensory thresholds reflecting the integrity of both large diameter, myelinated neurons (ie pressure, touch, vibration) and small diameter axons (ie hot and cold thermal sensation) were determined on the penis and finger. Data were compared across subjects with and without ED, controlling for age, hypertension and diabetes. The correlation of specific thresholds scores and IIEF values were also examined. Seventy-three patients who visited the academic urology clinics at Montefiore hospital were evaluated. All patients were required to complete the erectile function domain of the International Index of Erectile Function (IIEF) questionnaire: 20 subjects had no complaints of ED and scored within the 'normal' range on the IIEF. Patients were subsequently tested on their index finger and glans penis for vibration (Biothesiometer), pressure (Semmes-Weinstein monofilaments), spatial perception (Tactile Circumferential Discriminator), and warm and cold thermal thresholds (Physitemp NTE-2). Sensation of the glans penis, as defined by the examined sensory thresholds, was significantly diminished in patients with ED and these differences remained significant when controlling for age, diabetes and hypertension. In contrast, thresholds on the index finger were equivalent in the ED and non-ED groups. Threshold and IIEF scores were highly correlated, consistent with an association between diminished sensation and decreasing IIEF score (worse erectile functioning). These relations also remained significant when controlling for age, diabetes and hypertension. The findings demonstrate dysfunction of large and small diameter nerve fibers in patients with ED of all etiologies. Further, the neurophysiologic measures validate the use of the IIEF as an index of ED, as objective findings of sensory neuropathy were highly correlated with worse IIEF scores. The sensory threshold methods utilized represent novel, non-invasive and relatively simple procedures, which can be used in a longitudinal fashion to assess a patient's neurological response to therapies.