Clitoral sexual arousal: neuronal tracing study from the clitoris through the spinal tracts

Somatic and autonomic nerve density and distribution within the clitoris: an immunohistochemical study in adult female cadavers

INTRODUCTION AND HYPOTHESIS

Knowledge of clitoral neuroanatomy is critical to vulvar surgery. We sought to characterize the density and distribution of autonomic and somatic nerves supplying the clitoris.

METHODS

Pelvic tissue harvested from female cadavers was sectioned axially at three anatomic levels: the proximal aspect of the clitoral body (CB), the distal CB, and the glans. The CB, glans, and the surrounding connective tissue (dorsal, lateral, and ventral) were outlined microscopically. An area containing large nerve bundles dorsal to the CB, referred to as the dorsal nerve subregion, was analyzed separately. Double-immunofluorescent staining for beta III tubulin (βIIIT), a global axonal marker, and myelin basic protein (MBP), a myelinated nerve marker, was performed. Threshold-based automatic image-segmentation distinguished stained areas. Autonomic and somatic density were calculated as percentage of tissue stained with βIIIT alone, and βIIIT and MBP respectively. Comparisons were made using nonparametric Friedman tests.

RESULTS

Seven cadavers, aged 22-81, were examined. Somatic (mean 4.42%, SD ± 1.97) and autonomic (2.14% ± 2.42) nerve density was highest in the dorsal nerve subregion and dorsal region at the distal CB level. Compared with the CB, somatic density was higher in proximal (0.05% ± 0.03 vs 1.27% ± 0.69, p = 0.03) and distal (0.29% ± 0.25 vs 1.09% ± 0.41, p = 0.05) dorsal regions. Somatic density was greater in the glans than in the surrounding lateral (0.78% ± 0.47 vs 0.43% ± 0.23, p = 0.03) and ventral (0.78% ± 0.47 vs 0.52% ± 0.2, p = 0.03) regions. Autonomic density was greater than somatic in all areas, except for the dorsal nerve subregion.

CONCLUSIONS

Somatic and autonomic nerve density were greatest in a well-defined region dorsal to the CB. Surgical preservation of this region is critical for maintaining nerve supply to the clitoris.

Hormone-dependent sexual responses of female mice in response to manual genital stimulation

Although copulatory behavior is thought to have a strong innate basis in mice, there is also clear evidence that sexual experience shapes its expression. Reinforcement of behavior through rewarding genital tactile stimulation is a primary candidate mechanism for this modification. In rats, manual tactile clitoral stimulation is rewarding only when it is temporally distributed, which is hypothesized to result from an innate preference for species-typical copulatory patterning. Here we test this hypothesis using mice, which have a temporal copulatory pattern which is distinctly less temporally distributed than that of rats. Female mice received manual clitoral stimulation which was either temporally continuous every second, or stimulation which was temporally distributed, occurring every 5 s, This pattern of stimulation was paired with environmental cues in a conditioned place preference apparatus to assess reward. Neural activation in response to this stimulation was evaluated by measuring FOS immunoreactivity. Results indicated that both temporal patterns of clitoral stimulation were rewarding, but that continuous stimulation better reproduced brain activation associated with sexual reward. Furthermore, continuous, but not distributed stimulation elicited a lordosis response in some females, and this response increased within and across days. Sexual reward, neural activation and lordosis resulting from tactile genital stimulation were eliminated by ovariectomy and restored with combined 17β-estradiol and progesterone treatment but not 17β-estradiol treatment alone. These observations are consistent with the hypothesis that sexual reward resulting from species-typical genital tactile stimulation has a permissive effect on copulatory behavior of female mice.

How many nerve fibers innervate the human glans clitoris: a histomorphometric evaluation of the dorsal nerve of the clitoris

INTRODUCTION

It is frequently quoted in mainstream media that the clitoris has "8000 nerve endings." However, no study has yet quantified the number of nerve fibers (axons) innervating the human clitoris. The dorsal nerves of the clitoris (DNCs) are the primary source of sensation and somatic clitoral innervation. Therefore, reporting the number of axons in the DNCs is an important step in our understanding of clitoral innervation and sexual response with implications for many fields of medical practice. The purpose of this study is to quantify the mean number of axons in the human DNCs and to report the approximate mean number of nerve fibers that innervate the human glans clitoris.

METHODS

DNC samples were obtained from 7 transmasculine patients undergoing gender-affirming phalloplasty surgery. At the time of nerve coaptation, a small excess of the DNC (5 mm) was collected for analysis at the proximal level of the clitoral body, just distal of the emergence of the DNCs from underneath the pubic symphysis. Samples were placed into 3% glutaraldehyde fixative, postfixed in 1% osmium tetroxide, and serially dehydrated in ethanol and toluene. Samples were then embedded in araldite, sectioned on an ultramicrotome into 1-μm cross sections, and counterstained with 1% toluidine blue. Histomorphometric evaluation was performed at 1000x magnification with a Leitz Laborlux S microscope and image analysis software (Clemex Vision Professional) to obtain an axon counts. Descriptive statistics were performed to yield a mean and standard deviation of the number of axons in the DNCs. Assuming anatomic symmetry between bilateral DNCs, mean total number of somatic nerve fibers innervating the human glans clitoris was obtained by doubling the mean count of the DNCs.

RESULTS

Seven sample DNCs were collected. Of those, 5 were analyzed as 2 did not have sufficient nerve tissue present. The mean number of nerve fibers in the human DNCs was 5140 (SD = 218.4). The mean number of myelinated nerve fibers innervating the human clitoris was 10,281 (SD = 436.8).

CONCLUSION

This study is the first to report the number of axons in the human DNC, at a mean 5140. Given the bilateral nature of clitoral innervation and symmetry of anatomic structures, the approximate mean number of myelinated axons that innervate the human glans clitoris is 10,280. When the uncaptured unmyelinated fibers and contributions from the cavernosal innervation are accounted for, it is clear that far Moree than 8000 axons innervate the human clitoris.

Androgenic induction of penile features in postnatal female mouse external genitalia from birth to adulthood: Is the female sexual phenotype ever irreversibly determined?

Female mice were treated for 35 days from birth to 60 days postnatal (P0, [birth], P5, P10, P20 and adult [∼P60]) with dihydrotestosterone (DHT). Such treatment elicited profound masculinization the female external genitalia and development of penile features (penile spines, male urogenital mating protuberance (MUMP) cartilage, corpus cavernosum glandis, corporal body, MUMP-corpora cavernosa, a large preputial space, internal preputial space, os penis). Time course studies demonstrated that DHT elicited canalization of the U-shaped clitoral lamina to create a U-shaped preputial space, preputial lining epithelium and penile epithelium adorned with spines. The effect of DHT was likely due to signaling through androgen receptors normally present postnatally in the clitoral lamina and associated mesenchyme. This study highlights a remarkable male/female difference in specification and determination of urogenital organ identity. Urogenital organ identity in male mice is irreversibly specified and determined prenatally (prostate, penis, and seminal vesicle), whereas many aspects of the female urogenital organogenesis are not irreversibly determined at birth and in the case of external genitalia are not irreversibly determined even into adulthood, the exception being positioning of the female urethra, which is determined prenatally.

Persistent Genital Arousal Disorder: Two Case Studies and Exploration of a Novel Treatment Modality

Persistent genital arousal disorder (PGAD) is characterized by persistent unwanted feelings of sexual arousal that can be debilitating. Despite first being defined >20 years ago, the precise etiology and treatment of this disorder remain elusive. Mechanical disruption of nerves, neurotransmitter changes, and cyst formation have all been considered as etiologies involved with the development of PGAD. With limited and ineffective treatment modalities, many women live with their symptoms untreated or undertreated. To broaden the literature, we present two cases of PGAD and present a novel treatment modality of the disorder with the use of a pessary. Although there was subjective success in dampening the symptoms, they were not completely resolved. These findings open the door for the potential of similar treatments in the future.

Female Genital Variation Far Exceeds that of Male Genitalia: A Review of Comparative Anatomy of Clitoris and the Female Lower Reproductive Tract in Theria

A review of the literature on the anatomy of the lower female genital tract in therian mammals reveals, contrary to the general perception, a large amount of inter-specific variation. Variation in female external genitalia is anatomically more radical than that in the male genitalia. It includes the absence of whole anatomical units, like the cervix in many Xenarthra, or the absence of the urogenital sinus (UGS), as well as the complete spatial separation of the external clitoral parts from the genital canal (either vagina or UGS). A preliminary phylogenetic analysis shows two patterns. Some morphs are unique to early branching clades, like the absence of the cervix, while others arose multiple times independently, like the flattening out or loss of the UGS, or the extreme elongation of the clitoris. Based on available information, the ancestral eutherian configuration of the external female genitalia included a cervix, a single vaginal segment, a tubular UGS, and an unperforated clitoris close to the entrance of the genital canal. The evidence for either bilobed or unitary glandes clitorides is ambivalent. Despite the wealth of information available, many gaps in knowledge remain and will require a community-wide effort to come to a more robust model of female genital evolutionary patterns.

New method for early evaluation of clitoris innervation using clitoro-perineal reflex after feminizing genitoplasty in early childhood: a pilot-study

A major complication of feminizing genitoplasty in children is the loss of clitoral sensation with serious impact at adult life. We suggest a new method to evaluate the surgical results during childhood based on the bulbocavernosus or clitoro-perineal reflex (CPR). The afferent pathway of CPR implies the intact sensory receptors on the clitoral glans. Girls with congenital adrenal hyperplasia who were followed-up medically without surgery or who underwent feminizing genitoplasty with or without clitoroplasty were included (2002-2018). All clitoroplasties were standardized reduction clitoroplasty with preservation of neurovascular bundles associated with vaginoplasty and vestibuloplasty. Standardized examinations were prospectively performed including the CPR starting at one year postoperatively. The reflex was triggered by gentle touch of the glans by a cotton swab. Contraction of the perineal muscles was considered positive. Thirty-two children were operated at a median age of 8.6 months (5.8-12.1). Median follow-up (FU) was 3.9 years (1.3-6.4). Twenty-four patients had clitoroplasties: 17 were tested for CPR at one-year FU, and all had a positive test. Eight girls had genitoplasty without clitoral surgery, two of them were tested and were positive. Ten patients were managed without surgery, two of them were tested for the CPR and were positive. The reflex was always triggered easily and repeated at least twice during the FU. The clitoro-perineal reflex is a simple, non-invasive and reproducible test in early childhood and may serve as an early evaluation tool of clitoral innervation after feminizing genitoplasty. These results need to be confirmed at long term and completed at adult life.

Sexual Function of Men and Women With Spina Bifida: A Scoping Literature Review

INTRODUCTION

As most adults with spina bifida are either sexually active or interested in becoming sexually active, providers should understand how spina bifida impacts sexual function and options for treatment.

OBJECTIVES

The objective of this study is to summarize the current literature describing how features of spina bifida impact sexual function in men and women, effective available treatment options for sexual dysfunction, and to identify research gaps.

METHODS

Searches were conducted in PubMed, CINAHL Complete, PsychInfo, Cochrane Central, Scopus, and Web of Science Core Collection databases using keywords related to spina bifida and sexual function. 34 primary research studies were included.

RESULTS

Most men (56-96%) can achieve an erection, although it may be insufficient for penetration. Although 50-88% ejaculate, it is often dripping, retrograde, or insensate. Twenty percent to 67% achieve orgasm. Generally, men with lower lesions and intact sacral reflexes have better outcomes, although some men with all levels of lesion report good function. Sildenafil is efficacious at treating erectile dysfunction for most men. The "TO-MAXimize sensation, sexuality, and quality of life" procedure may improve sexual function in selected men with low-level lesions. Female sexual function and treatment is less well understood. Women may experience decreased arousal, difficulties with orgasm, and pain. No treatment has been studied in women. Bowel and bladder incontinence during intercourse appears to be bothersome to men and women. Although both men and women have diminished sexual satisfaction, their sexual desire appears to be least impacted. Present studies are limited by studies' small, heterogeneous populations, the misuse of validated questionnaires in the sexually inactive population, and the lack of a validated questionnaire specific to people with spina bifida.

CONCLUSIONS

Spina bifida impacts the sexual function of both men and women. Future studies should seek a better understanding of female sexual function and treatment, use validated questionnaires appropriately, and ultimately create a validated sexual function questionnaire specific to this population. Streur CS, Corona L, Smith JE, et al. Sexual Function of Men and Women With Spina Bifida: A Scoping Literature Review. Sex Med Rev 2021;9:244-266.

Persistent genital arousal disorder: a special sense neuropathy

Introduction

Persistent genital arousal (PGAD) is a syndrome of unprovoked sexual arousal/orgasm of uncertain cause primarily reported in female patients. Most patients are referred for mental-health treatment, but as research suggests associations with neurological symptoms and conditions, there is need to analyze cases comprehensively evaluated by neurologists.

Methods

The IRB waived consent requirements for this retrospective university-hospital study. We extracted and analyzed neurological symptoms, test, and treatment results from all qualifying participants' records and recontacted some for details.

Results

All 10 participants were female; their PGAD symptoms began between ages 11 to 70 years. Two patterns emerged: 80% reported daily out-of-context sexual arousal episodes (≤30/day) that usually included orgasm and 40% reported lesser, often longer-lasting, nonorgasmic arousals. Most also had symptoms consistent with sacral neuropathy-70% had urologic complaints and 60% had neuropathic perineal or buttock pain. In 90% of patients, diagnostic testing identified anatomically appropriate and plausibly causal neurological lesions. Sacral dorsal-root Tarlov cysts were most common (in 4), then sensory polyneuropathy (2). One had spina bifida occulta and another drug-withdrawal effect as apparently causal; lumbosacral disc herniation was suspected in another. Neurological treatments cured or significantly improved PGAD symptoms in 4/5 patients, including 2 cures.

Conclusions

Although limited by small size and referral bias to neurologists, this series strengthens associations with Tarlov cysts and sensory polyneuropathy and suggests new ones. We hypothesize that many cases of PGAD are caused by unprovoked firing of C-fibers in the regional special sensory neurons that subserve sexual arousal. Some PGAD symptoms may share pathophysiologic mechanisms with neuropathic pain and itch.

Refractory Sexual Arousal Subsequent to Sacral Neuromodulation

Background

Sacral neuromodulation has become a widely used treatment for lower urinary tract symptom and dysfunction. It has been observed to benefit sexual function in the domains of arousal and desire. Studies have yet to report markedly increased arousal symptoms as an adverse effect.

Case

We present the case of a 57-year-old woman who developed symptomatic persistent genital arousal following implantation of a neuromodulator. Despite device reprogramming, a trial of the device being shut off, and eventual device removal, she continued to have residual new-onset undesired genital hyper-arousal symptoms.

Conclusion

Our patient demonstrated markedly increased and persistent arousal symptoms that may be the result of upregulated or alternative activation of sacral nerve pathways. While other case reports describe improvement in persistent genital arousal disorder symptoms through neuromodulation, no studies mention hyperarousal symptoms as an adverse side effect after sacral neuromodulator placement nor persistence despite removal of the implant.

Anatomy of mole external genitalia: Setting the record straight

Anatomy of male and female external genitalia of adult mice (Mus musculus) and broad-footed moles (Scapanus latimanus) was re-examined to provide more meaningful anatomical terminology. In the past the perineal appendage of male broad-footed moles has been called the penis, while the female perineal appendage has been given several terms (e.g. clitoris, penile clitoris, peniform clitoris and others). Histological examination demonstrates that perineal appendages of male and female broad-footed moles are the prepuce, which in both sexes are covered externally with a hair-bearing epidermis and lacks erectile bodies. The inner preputial epithelium is non-hair-bearing and defines the preputial space in both sexes. The penis of broad-footed moles lies deep within the preputial space, is an "internal organ" in the resting state and contains the penile urethra, os penis, and erectile bodies. The clitoris of broad-footed moles is defined by a U-shaped clitoral epithelial lamina. Residing within clitoral stroma encompassed by the clitoral epithelial lamina is the corpus cavernosum, blood-filled spaces and the urethra. External genitalia of male and female mice are anatomically similar to that of broad-footed moles with the exception that in female mice the clitoris contains a small os clitoridis and lacks defined erectile bodies, while male mice have an os penis and a prominent distal cartilaginous structure within the male urogenital mating protuberance (MUMP). Clitori of female broad-footed moles lack an os clitoridis but contain defined erectile bodies, while male moles have an os penis similar to the mouse but lack the distal cartilaginous structure.

Animal Models for the Study of Female Sexual Dysfunction

INTRODUCTION

Significant progress has been made in elucidating the physiological and pharmacological mechanisms of female sexual function through preclinical animal research. The continued development of animal models is vital for the understanding and treatment of the many diverse disorders that occur in women.

AIM

To provide an updated review of the experimental models evaluating female sexual function that may be useful for clinical translation.

METHODS

Review of English written, peer-reviewed literature, primarily from 2000 to 2012, that described studies on female sexual behavior related to motivation, arousal, physiological monitoring of genital function and urogenital pain.

MAIN OUTCOMES MEASURES

Analysis of supporting evidence for the suitability of the animal model to provide measurable indices related to desire, arousal, reward, orgasm, and pelvic pain.

RESULTS

The development of female animal models has provided important insights in the peripheral and central processes regulating sexual function. Behavioral models of sexual desire, motivation, and reward are well developed. Central arousal and orgasmic responses are less well understood, compared with the physiological changes associated with genital arousal. Models of nociception are useful for replicating symptoms and identifying the neurobiological pathways involved. While in some cases translation to women correlates with the findings in animals, the requirement of circulating hormones for sexual receptivity in rodents and the multifactorial nature of women's sexual function requires better designed studies and careful analysis. The current models have studied sexual dysfunction or pelvic pain in isolation; combining these aspects would help to elucidate interactions of the pathophysiology of pain and sexual dysfunction.

CONCLUSIONS

Basic research in animals has been vital for understanding the anatomy, neurobiology, and physiological mechanisms underlying sexual function and urogenital pain. These models are important for understanding the etiology of female sexual function and for future development of pharmacological treatments for sexual dysfunctions with or without pain. Marson L, Giamberardino MA, Costantini R, Czakanski P, and Wesselmann U. Animal models for the study of female sexual dysfunction. Sex Med Rev 2013;1:108-122.

The effect of sacral neuromodulation on pudendal nerve function and female sexual function

AIMS

To quantify changes in pudendal nerve function with sacral neuromodulation (SNM). To understand the relationship of pudendal nerve function to SNM treatment response for overactive bladder. To assess the relationship between female sexual function and pudendal nerve function after SNM.

METHODS

Women undergoing SNM between January 2010 and May 2011 were enrolled. Baseline pudendal nerve terminal motor latencies (PNTML) were measured bilaterally. Subjects underwent peripheral nerve evaluation (PNE) prior to SNM therapy. PNTML was measured at 1 and 6 weeks after sacral neuromodulator implant. Women who did not undergo permanent implantation were reassessed at the end of the 1-week PNE testing phase. Pelvic floor and sexual function questionnaires were administered at baseline and follow-up to assess pelvic floor and sexual function.

RESULTS

Of 34 women enrolled, 31 were evaluated. Mean age was 67.4 ± 14.2 years with 29/34 (85.3%) treated for refractory overactive bladder. Thirty of 31 (96.7%) went on to a permanent implant. PNE success rate was 73.5% (25/33). Mean PNTML changed from 2.74 ± 0.52 msec at baseline to 2.57 ± 0.50 msec at 6 weeks postop (P = 0.198). Baseline amplitude remained stable at 1 and 6 weeks. At 6 weeks PISQ-12 scores showed improved sexual function (P = 0.034) and PFDI-20 and PFIQ-7 scores showed improved pelvic floor, colorectal and urinary symptoms (P < 0.05).

CONCLUSIONS

Women with refractory overactive bladder and non-obstructive urinary retention have abnormal pudendal nerve function, which showed a non-significant trend toward improvement after SNM. Sexually active women undergoing sacral neuromodulation experienced improvement in sexual function. Quality of life improved due to improvement in urinary and colorectal function.

Female reproductive tract pain: targets, challenges, and outcomes

Pain from the female reproductive tract (FRT) is a significant clinical problem for which there are few effective therapies. The complex neuroanatomy of pelvic organs not only makes diagnosis of pelvic pain disorders difficult but represents a challenge to development of targeted therapies. A number of potential therapeutic targets have been identified on sensory neurons supplying the FRT but our knowledge on the basic neurophysiology of these neurons is limited compared with other viscera. Until this is addressed we can only guess if the new experimental therapies proposed for somatic, gastrointestinal, or bladder pain will translate to the FRT. Once suitable therapeutic targets become clear, the next challenge is drug delivery. The FRT represents a promising system for topical drug delivery that could be tailored to act locally or systemically depending on formulation. Development of these therapies and their delivery systems will need to be done in concert with more robust in vivo and in vitro models of FRT pain.

Congenital Adrenal Hyperplasia: Review from a Surgeon's Perspective in the Beginning of the Twenty-First Century

Congenital adrenal hyperplasia (CAH) most commonly due to 21-hydroxylase deficiency is the most common type of disorder of sex development. This review will focus on CAH addressing historical and current surgical techniques with their anatomical foundations, with special attention to long-term results and outcomes on sexual function, patient satisfaction, patient attitude toward surgery, and ongoing controversies in management of these patients.

Sexual function in adult life following Passerini-Glazel feminizing genitoplasty in patients with congenital adrenal hyperplasia

PURPOSE

We assessed external genitalia sensitivity and sexual function in adults with congenital adrenal hyperplasia who had undergone Passerini-Glazel feminizing genitoplasty as children, and compared them to a control group of healthy counterparts.

MATERIALS AND METHODS

Inclusion criteria were congenital adrenal hyperplasia, Passerini-Glazel feminizing genitoplasty, adult age and penetrative vaginal intercourse. Thermal and vibratory sensitivity of the clitoris, vagina and labia minora were analyzed using the Genito Sensory Analyzer (Medoc Ltd., Minnetonka, Minnesota). Psychosexual outcome was assessed with the Beck Depression Inventory, Zung Self-Rating Anxiety Scale, Female Sexual Distress Scale and Female Sexual Function Index. Matched analyses were performed to compare outcomes in patients to controls (healthy medical students). All statistical tests were performed using SPSS®, version 18.0 RESULTS: A total of 12 patients (10%) entered the study. Thermal and vibratory clitoral sensitivity was significantly decreased in all patients compared to healthy controls (p <0.01). There was no difference in thermal or vibratory vaginal sensitivity between patients and controls. On the Female Sexual Distress Scale 11 patients (91.6%) and 11 controls (91.6%) described a stable satisfactory relationship. All patients reported active sexual desire, good arousal, adequate lubrication and orgasm. No significant difference in Female Sexual Function Index global score or single domain scores was observed between patients and controls.

CONCLUSIONS

Although clitoral sensitivity in sexually active patients with congenital adrenal hyperplasia treated with Passerini-Glazel feminizing genitoplasty is significantly reduced compared to controls, sexual function in those patients is not statistically or clinically significantly different from their healthy counterparts. Finally, 1-stage Passerini-Glazel feminizing genitoplasty seems to allow normal adult sexual function.

Bladder, bowel, and sexual dysfunction in Parkinson's disease

Bladder dysfunction (urinary urgency/frequency), bowel dysfunction (constipation), and sexual dysfunction (erectile dysfunction) (also called “pelvic organ” dysfunctions) are common nonmotor disorders in Parkinson's disease (PD). In contrast to motor disorders, pelvic organ autonomic dysfunctions are often nonresponsive to levodopa treatment. The brain pathology causing the bladder dysfunction (appearance of overactivity) involves an altered dopamine-basal ganglia circuit, which normally suppresses the micturition reflex. By contrast, peripheral myenteric pathology causing slowed colonic transit (loss of rectal contractions) and central pathology causing weak strain and paradoxical anal sphincter contraction on defecation (PSD, also called as anismus) are responsible for the bowel dysfunction. In addition, hypothalamic dysfunction is mostly responsible for the sexual dysfunction (decrease in libido and erection) in PD, via altered dopamine-oxytocin pathways, which normally promote libido and erection. The pathophysiology of the pelvic organ dysfunction in PD differs from that in multiple system atrophy; therefore, it might aid in differential diagnosis. Anticholinergic agents are used to treat bladder dysfunction in PD, although these drugs should be used with caution particularly in elderly patients who have cognitive decline. Dietary fibers, laxatives, and “prokinetic” drugs such as serotonergic agonists are used to treat bowel dysfunction in PD. Phosphodiesterase inhibitors are used to treat sexual dysfunction in PD. These treatments might be beneficial in maximizing the patients' quality of life.

How generalized CNS arousal strengthens sexual arousal (and vice versa)

Heightened states of generalized CNS arousal are proposed here to facilitate sexual arousal in both males and females. Genetic, pharmacologic and biophysical mechanisms by which this happens are reviewed. Moreover, stimulation of the genital epithelia, as triggers of sex behavior, is hypothesized to lead to a greater generalized arousal in a manner that intensifies sexual motivation. Finally, launched from histochemical studies intended to characterize cells in the genital epithelium, a surprising idea is proposed that links density of innervation with the efficiency of wound healing and with the capacity of that epithelium to stimulate generalized CNS arousal. Thus, bidirectional arousal-related mechanisms that foster sexual behaviors are envisioned as follows: from specific to generalized (as with genital stimulation) and from generalized to specific.

Somatic genital reflexes in rats with a nod to humans: anatomy, physiology, and the role of the social neuropeptides

Somatic genital reflexes such as ejaculation and vaginocervical contractions are produced through the striated muscles associated with the genitalia. The coordination of these reflexes is surprisingly complex and involves a number of lumbosacral spinal and supraspinal systems. The rat model has been proven to be an excellent source of information regarding these mechanisms, and many parallels to research in humans can be drawn. An understanding of the spinal systems involving the lumbosacral spinal cord, both efferent and afferent, has been generated through decades of research. Spinal and supraspinal mechanisms of descending excitation, through a spinal ejaculation generator in the lumbar spinal cord and thalamus, and descending inhibition, through the ventrolateral medulla, have been identified and characterized both anatomically and physiologically. In addition, delineation of the neural circuits whereby ascending genitosensory information regarding the regulation of somatic genital reflexes is relayed supraspinally has also been the topic of recent investigation. Lastly, the importance of the "social neuropeptides" oxytocin and vasopressin in the regulation of somatic genital reflexes, and associated sociosexual behaviors, is emerging. This work not only has implications for understanding how nervous systems generate sexual behavior but also provides treatment targets for sexual dysfunction in people.

Innervation of the labia minora of prepubertal girls

INTRODUCTION

Surgical and histologic sources of information give little reference to innervation, vascular, and epithelial details of the labia minora. Little is known about areas of nerve density, epithelial qualities, and vascular compartments of the labial minora that contribute to sexual arousal and orgasm. Surgical procedure development and counsel about surgical risks related to labioplasty and surgical flaps created from labial tissue may be based on inadequate information.

METHODS

Labial samples from 10 normal girls (aged 2-9 years) who underwent surgery for labial fusion utilized waste tissue strips for immunohistochemical identification of S-100 and neuronal nitric oxide synthase (nNOS) in the labia minora.

RESULTS

Vascular and lymphatic plexus lie within the reticular dermis, which contains a dense mesh of nerve fibers with a higher concentration of nerve fiber at the level of the subepithelial plexus. Dense innervations are located at the epidermis, extending along the basal and spinous layers of the epithelium of labia minora. Nerve bundles in the papillary dermis are associated with sebaceous and eccrine glands and nerve terminals located throughout the epithelium. The introital epithelium of the labia minora is highly innervated with widespread and intense staining, detected in the introital border of the labia minora versus the external one. The dermis appeared to display S-100 and nNOS immunolabelling. S-100 was also immunopositive in the epidermis.

CONCLUSION

Labia minora is highly innervated along its entire edge. Related vascular compartment tissue involved in engorgement during sexual arousal makes this tissue important for sexual response. Labioplasty risks removal of tissue with an important contribution to sensory sexual arousal. Movement of labial tissue during genitoplasty may have different sensory outcomes dependent on which labial surface is used.

Reproductive behaviors: new developments in concepts and in molecular mechanisms progress in brain research, Luciano Martini, editor, January 19, 2010

New developments in the analysis of mechanisms for reproductive behaviors are reviewed. Conceptually, the concept of generalized arousal (GA) of the central nervous system (CNS) is considered. Breeding for high and low GA, we show an impact of GA on sexual arousal of male mice, and also find that the structure of GA in the CNS of males and females is not the same. Further, we propose, theoretically, that among epithelial tissues in humans, there are correlations among their innervation densities and their ability to trigger arousal. In new technical developments, we analyze transcriptional effects of estrogens in the hypothalamic neurons that regulate lordosis behavior. The rapid effect of estradiol to increase acetylation of histones in ventromedial hypothalamic neurons could be tied into transcriptional activation, but the effect of estradiol to increase methylation of histone 3, lysine 9 (H3K9) is puzzling. This work seeks to discover the coactivator dynamics underlying transcriptional effects of estrogens on sex behavior.

The somatosensory representation of the human clitoris: an fMRI study

We studied the central representation of pudendal afferents arising from the clitoral nerves in 15 healthy adult female subjects using electrical dorsal clitoral nerve stimulation and fMRI. As a control body region, we electrically stimulated the right hallux in eight subjects. In a block design experiment, we applied bilateral clitoral stimulation and unilateral (right) hallux stimulation. Activation maps were calculated for the contrasts 'electrical dorsal clitoral nerve stimulation versus rest' and 'electrical hallux stimulation versus rest'. A random-effect group analysis for the clitoral stimulation showed significant activations bilateral in the superior and inferior frontal gyri, insulae and putamen and in the postcentral, precentral and inferior parietal gyri (including the primary and secondary somatosensory cortices). No activation was found on the mesial surface of the postcentral gyrus. For the hallux, activations occurred in a similar neuronal network but the activation in the primary somatosensory cortex was localized in the inter-hemispheric fissure. The results of this study demonstrate that the central representation of pudendal afferents arising from the clitoral nerves and sensory inputs from the hallux can be studied and distinguished from each other by fMRI. From the somatotopic order described in the somatosensory homunculus one would expect for electrical clitoral nerve stimulation activation of the mesial wall of the postcentral gyrus. In contrast, we found activations on the lateral surface of the postcentral gyrus.