Identification of a potential ejaculation generator in the spinal cord

Orgasms, sexual pleasure, and opioid reward mechanisms

INTRODUCTION

Sexual activity produces pleasure related to sexual arousal, desire, and genitosensory and erogenous stimulation. Orgasms produce a whole brain and body rush of ecstatic pleasure followed by relaxation and refractoriness. This pleasure results from the activation of neurochemical reward pathways in the brain. This is differentiated by spinal pathways that control climax, the particular motor movements of the pelvic floor and the experience of tension release.

OBJECTIVES

To relate the activation of key neurochemical reward and bonding systems, notably dopamine, oxytocin, and opioids, to the pleasure of sexual activity in general and orgasms in particular.

METHODS

A narrative review of the neurochemical and neuroanatomical mechanisms activated during sexual stimulation and orgasm in rats and humans, and how they are related overall to the generation of sexual pleasure and reward.

RESULTS

Appetitive sexual pleasure involves the activation of dopamine and oxytocin release in hypothalamic and mesolimbic regions that regulate sexual arousal and desire, and are reinforced by localized opioid activity. Orgasms are thought to result in part from a massive release of opioids into these regions that inhibits dopamine and oxytocin transmission, but that initiates molecular changes to sensitize both systems and induce sexually conditioned place and partner preferences. Serotonin is also activated at orgasm and contributes to feelings of satiety and refractoriness. Orgasm disorders are distressing, cause resentment and conflict in a relationship, and diminish overall sexual health and well-being.

CONCLUSIONS

Orgasms are an important component of sexual pleasure for humans and perhaps all vertebrates. Endogenous opioids like β-endorphin that bind to mu opioid receptors are likely responsible for sexual pleasure and reward.

Spinal cord epidural stimulation for male sexual function in spinal cord injured rats

BACKGROUND

95% of men with spinal cord injuries exhibit difficulties with sexual function, including erectile dysfunction, anejaculation, retrograde ejaculation, poor ejaculatory force, and poor sperm quality.

AIM

The primary goal is to determine if well-established interventions, such as spinal cord epidural stimulation, are a feasible treatment for sexual dysfunction and if locomotor recovery training can be used to improve ejaculatory function in a rodent model of spinal cord injury (SCI).

METHODS

Male Wistar rats underwent thoracic laminectomies (shams), spinal cord transections, or moderate spinal cord contusion injuries. In urethane-anesthetized rodents, terminal spinal cord epidural stimulation was performed to target the mid-lumbar level spinal generator for ejaculation (SGE) in animals with transection spinal cord injuries at 3-, 14-, or 70-days post-injury and in animals with sham surgeries and spinal cord contusions at 70 days post-injury. The impact of locomotor training frequency was examined in two groups of rats with spinal cord contusion, which underwent 1-hr of assisted plantar stepping on a treadmill, training two or five times weekly for 6 weeks. Terminal experiments in all groups were followed by measures of sperm concentration and post-mortem testicular weight and morphology.

OUTCOMES

Spinal cord epidural stimulation consistently induced the expulsion phase of ejaculation, and occasionally the emission phase of ejaculation in rats with chronic SCI.

RESULTS

All animals were most responsive to spinal cord epidural stimulation combined with manual stimulation to induce ejaculation, with chronic injury resulting in the most consistent responses. Locomotor training improved response rates to spinal cord epidural stimulation, with intermittent training resulting in the most consistent induction of both the emission and expulsion phases of ejaculation. Sperm concentration was impacted by injury completeness and time-post injury, which was lowest in the chronic complete transection group of rats. Locomotor training resulted in an overall increase in sperm concentration, with 2 days per week of training resulting in a significant improvement of sperm motility.

CLINICAL IMPLICATIONS

Spinal cord epidural stimulation combined with locomotor training is a feasible intervention for individuals with SCI who seek to regain sexual function.

STRENGTHS AND LIMITATIONS

Although we have anecdotal reports of non-targeted L3 spinal cord epidural stimulation inducing ejaculation in humans having spinal cord injuries, the current outcomes may be underestimated as stimulation was carried out in anesthetized animals.

CONCLUSION

Spinal cord epidural stimulation to target the SGE is a feasible intervention for sexual dysfunction following SCI.

Leptin action on ARC-PVN neural circuit regulates ejaculation behavior by altering sympathetic neuroplasticity

BACKGROUND

Although some studies have revealed the close relationship between leptin and premature ejaculation in clinical practice, whether and how leptin participates in the regulation of ejaculatory behaviors are still unknown.

OBJECTIVE

To explore the role of leptin on ejaculatory behaviors and its underlying mechanism.

MATERIALS AND METHODS

Copulation behavior tests were performed after acute and chronic leptin administration at peripheral and central levels. To compare changes in sympathetic nervous system activity, lumbar sympathetic nervous activity, serum noradrenaline levels, and the distribution of sympathetic fibers in vas deferens and seminal vesicles were analyzed. Construction of virus vector, immunohistochemistry, and optogenetics techniques were used to explore the neural circuit mechanism. The density of dendritic spines in parvocellular region of paraventricular nucleus was measured by Golgi staining.

RESULTS

Acute administration of leptin had no effect on ejaculation behavior in male mice. However, both mount latency and ejaculation latency were significantly shortened, even if serum leptin decreased to normal level, after chronic administration of leptin at peripheral or central level. Additionally, sympathetic fibers in vas deferens and seminal vesicles obviously increased, in which arcuate nucleus‒paraventricular nucleus circuit and glutamatergic neurons in paraventricular nucleus played an important role. Dendritic spine density in parvocellular region increased after chronic leptin administration.

DISCUSSION AND CONCLUSION

The role of leptin in regulating ejaculation behavior was chronic, not acute, in which leptin chronically modulated sympathetic neuroplasticity via arcuate nucleus‒paraventricular nucleus circuit and glutamatergic neurons in paraventricular nucleus and promoted ejaculatory behaviors. Increased dendritic spine density in parvocellular region of paraventricular nucleus may be involved as well.

Epidural spinal cord stimulation can facilitate ejaculatory response in spinal cord injury individuals: a report of two cases

BACKGROUND

The recovery of autonomic functions and the ability to reproduce in particular is of the highest priority to individuals with spinal cord injury (SCI). The potential of epidural spinal cord stimulation (ESCS) for promoting recovery of sensorimotor functions in the chronic phase of SCI has long been studied. In recent years, several studies have emerged confirming the positive effect of ESCS also on the cardiovascular system and neurogenic bladder and bowel. However, the potential of ESCS in restoring sexual function, especially ejaculation, has not yet been addressed.

CASE REPORT

Two cases of people with chronic sensorimotor complete SCI in the 4th thoracic spinal segment are presented. Both men were also diagnosed with severe erectile dysfunction and anejaculation. Thanks to ESCS, Participant 1 successfully restored the ejaculatory reflex using PVS in his home environment. His outcome was subsequently verified under clinical conditions. During ESCS, Participant 1 was also able to achieve ejaculation by masturbation; moreover, he conceived a child naturally without the need for IVF. In Participant 2, we then demonstrated the same effect of ESCS on the restoration of the ejaculatory reflex when targeting the stimulation to the same spinal segment.

CONCLUSION

This is the first report on the potential of ESCS for restoring the ability to ejaculate in individuals with complete SCI. Confirmation of these results could significantly reduce the need for assisted reproduction and improve the quality of life of men after SCI in the future.

Krause corpuscles are genital vibrotactile sensors for sexual behaviours

Krause corpuscles, which were discovered in the 1850s, are specialized sensory structures found within the genitalia and other mucocutaneous tissues1-4. The physiological properties and functions of Krause corpuscles have remained unclear since their discovery. Here we report the anatomical and physiological properties of Krause corpuscles of the mouse clitoris and penis and their roles in sexual behaviour. We observed a high density of Krause corpuscles in the clitoris compared with the penis. Using mouse genetic tools, we identified two distinct somatosensory neuron subtypes that innervate Krause corpuscles of both the clitoris and penis and project to a unique sensory terminal region of the spinal cord. In vivo electrophysiology and calcium imaging experiments showed that both Krause corpuscle afferent types are A-fibre rapid-adapting low-threshold mechanoreceptors, optimally tuned to dynamic, light-touch and mechanical vibrations (40-80 Hz) applied to the clitoris or penis. Functionally, selective optogenetic activation of Krause corpuscle afferent terminals evoked penile erection in male mice and vaginal contraction in female mice, while genetic ablation of Krause corpuscles impaired intromission and ejaculation of males and reduced sexual receptivity of females. Thus, Krause corpuscles of the clitoris and penis are highly sensitive mechanical vibration detectors that mediate sexually dimorphic mating behaviours.

Neurophysiology of male sexual arousal-Behavioral perspective

In the presented review, we analyzed the physiology of male sexual arousal and its relation to the motivational aspects of this behavior. We highlighted the distinction between these processes based on observable physiological and behavioral parameters. Thus, we proposed the experimentally applicable differentiation between sexual arousal (SA) and sexual motivation (SM). We propose to define sexual arousal as an overall autonomic nervous system response leading to penile erection, triggered selectively by specific sexual cues. These autonomic processes include both spinal and supraspinal neuronal networks, activated by sensory pathways including information from sexual partner and sexual context, as well as external and internal genital organs. To avoid misinterpretation of experimental data, we also propose to precise the term "sexual motivation" as all actions performed by the individual that increase the probability of sexual interactions or increase the probability of exposition to sexual context cues. Neuronal structures such as the amygdala, bed nucleus of stria terminalis, hypothalamus, nucleus raphe, periaqueductal gray, and nucleus paragigantocellularis play crucial roles in controlling the level of arousal and regulating peripheral responses via specific autonomic effectors. On the highest level of CNS, the activity of cortical structures involved in the regulation of the autonomic nervous system, such as the insula and anterior cingulate cortex, can visualize an elevated level of SA in both animal and human brains. From a preclinical perspective, we underlie the usefulness of the non-contact erection test (NCE) procedure in understanding factors influencing sexual arousal, including studies of sexual preference in animal models. Taken together results obtained by different methods, we wanted to focus attention on neurophysiological aspects that are distinctly related to sexual arousal and can be used as an objective parameter, leading to higher translational transparency between basic, preclinical, and clinical studies.

Orexin receptors in paraventricular nucleus influence sexual behavior via regulating the sympathetic outflow in males

BACKGROUND

Orexins are hypothalamic neuropeptides associated with various neurophysiological activities such as sleep, arousal, and reward. However, there are few studies investigating the relationships between orexin receptors in the paraventricular nucleus and sexual behaviors.

OBJECTIVES

To explore the roles of orexin receptors in the paraventricular nucleus on sexual behaviors and uncover its potential mechanisms in males.

MATERIALS AND METHODS

Orexin A, orexin 1 receptor antagonist SB334867, and orexin 2 receptor antagonist TCS-OX2-29 were microinjected into the paraventricular nucleus to investigate the effects of orexin receptors on copulatory behavior testing of C57BL/6 mice. To explore if ejaculation could activate orexin 1 receptor-expressing neurons in the paraventricular nucleus, fluorescence immunohistochemical double staining was utilized. The levels of serum norepinephrine were measured and the lumbar sympathetic nerve activity was recorded to reflect the sympathetic nervous system activity. Moreover, the bulbospongiosus muscle-electromyogram was recorded and analyzed. To test whether perifornical/lateral hypothalamic area orexinergic neurons directly projected to the paraventricular nucleus, virus retrograde tracing technology was utilized.

RESULTS

Orexin A significantly enhanced sexual performance by shortening the intromission and ejaculation latencies, and increasing the mount and intromission frequencies, while the opposite outcomes appeared with SB334867. However, TCS-OX2-29 had no significant effects on sexual behaviors. Moreover, orexin A increased lumbar sympathetic nerve activity and the levels of serum norepinephrine, while SB334867 decreased lumbar sympathetic nerve activity and norepinephrine, which caused a significant decrease in sympathetic nervous system outflow. Meanwhile, a robust increase in the bulbospongiosus muscle-electromyogram activity was identified after microinjecting orexin A. Furthermore, cFos immunopositive cells were increased and double stained with orexin 1 receptor-expressing neurons in the mating group. Additionally, the retrograde tracing results demonstrated that orexinergic neurons in the perifornical/lateral hypothalamic area directly projected to the paraventricular nucleus.

CONCLUSIONS

Orexin 1 receptor in the paraventricular nucleus could influence the ejaculatory reflex via mediating the sympathetic nervous system activity, which might be of great importance in the treatment of premature ejaculation in the future.

Neuropeptidergic control circuits in the spinal cord for male sexual behaviour: Oxytocin-gastrin-releasing peptide systems

The neuropeptidergic mechanisms controlling socio-sexual behaviours consist of complex neuronal circuitry systems in widely distributed areas of the brain and spinal cord. At the organismal level, it is now becoming clear that "hormonal regulations" play an important role, in addition to the activation of neuronal circuits. The gastrin-releasing peptide (GRP) system in the lumbosacral spinal cord is an important component of the neural circuits that control penile reflexes in rats, circuits that are commonly referred to as the "spinal ejaculation generator (SEG)." Oxytocin, long known as a neurohypophyseal hormone, is now known to be involved in the regulation of socio-sexual behaviors in mammals, ranging from social bonding to empathy. However, the functional interaction between the SEG neurons and the hypothalamo-spinal oxytocin system remains unclear. Oxytocin is known to be synthesised mainly in hypothalamic neurons and released from the posterior pituitary into the circulation. Oxytocin is also released from the dendrites of the neurons into the hypothalamus where they have important roles in social behaviours via non-synaptic volume transmission. Because the most familiar functions of oxytocin are to regulate female reproductive functions including parturition, milk ejection, and maternal behaviour, oxytocin is often thought of as a "feminine" hormone. However, there is evidence that a group of parvocellular oxytocin neurons project to the lower spinal cord and control male sexual function in rats. In this report, we review the functional interaction between the SEG neurons and the hypothalamo-spinal oxytocin system and effects of these neuropeptides on male sexual behaviour. Furthermore, we discuss the finding of a recently identified, localised "volume transmission" role of oxytocin in the spinal cord. Findings from our studies suggest that the newly discovered "oxytocin-mediated spinal control of male sexual function" may be useful in the treatment of erectile and ejaculatory dysfunction.

Krause corpuscles of the genitalia are vibrotactile sensors required for normal sexual behavior

Krause corpuscles, first discovered in the 1850s, are enigmatic sensory structures with unknown physiological properties and functions found within the genitalia and other mucocutaneous tissues. Here, we identified two distinct somatosensory neuron subtypes that innervate Krause corpuscles of the mouse penis and clitoris and project to a unique sensory terminal region of the spinal cord. Using in vivo electrophysiology and calcium imaging, we found that both Krause corpuscle afferent types are A-fiber rapid-adapting low-threshold mechanoreceptors, optimally tuned to dynamic, light touch and mechanical vibrations (40-80 Hz) applied to the clitoris or penis. Optogenetic activation of male Krause corpuscle afferent terminals evoked penile erection, while genetic ablation of Krause corpuscles impaired intromission and ejaculation of males as well as reduced sexual receptivity of females. Thus, Krause corpuscles, which are particularly dense in the clitoris, are vibrotactile sensors crucial for normal sexual behavior.

Understanding and treating ejaculatory dysfunction in men with diabetes mellitus

Diabetes mellitus is a rapidly rising metabolic disorder with important systemic complications. Global figures have demonstrated the prevalence of diabetes mellitus has almost quadrupled from 108 million in 1980 to 422 million in 2014, with a current prevalence of over 525 million. Of the male sexual dysfunction resulting from diabetes mellitus, significant focus is afforded to erectile dysfunction. Nevertheless, ejaculatory dysfunction constitutes important sexual sequelae in diabetic men, with up to 35%-50% of men with diabetes mellitus suffering from ejaculatory dysfunction. Despite this, aspects of its pathophysiology and treatment are less well understood than erectile dysfunction. The main disorders of ejaculation include premature ejaculation, delayed ejaculation, anejaculation and retrograde ejaculation. Although ejaculatory dysfunction in diabetes mellitus can have complex multifactorial aetiology, understanding its pathophysiological mechanisms has facilitated the development of therapies in the management of ejaculatory dysfunction. Most of our understanding of its pathophysiology is derived from diabetic animal models; however, observational studies in humans have also provided useful information in elucidating important associative factors potentially contributing to ejaculatory dysfunction in diabetic men. These have provided the potential for more tailored treatment regimens in patients depending on the ejaculatory disorder, other co-existing sequelae of diabetes mellitus, specific metabolic factors as well as the need for fertility treatment. However, evidence for treatment of ejaculatory dysfunction, especially delayed ejaculation and retrograde ejaculation, is based on low-level evidence comprising small sample-size series and retrospective or cross-sectional studies. Whilst promising findings from large randomised controlled trials have provided strong evidence for the licensed treatment of premature ejaculation, similar robust studies are needed to accurately elucidate factors predicting ejaculatory dysfunction in diabetes mellitus, as well as for the development of pharmacotherapies for delayed ejaculation and retrograde ejaculation. Similarly, more contemporary robust data are required for fertility outcomes in these patients, including methods of sperm retrieval and assisted reproductive techniques in retrograde ejaculation.

Spinal Transection Switches the Effect of Metabotropic Glutamate Receptor Subtype 7 from the Facilitation to Inhibition of Ejaculation

Metabotropic glutamate receptor subtype 7 (mGluR7) is a member of the group III mGluRs, which localize to presynaptic active zones of the central nervous system. We previously reported that mGluR7 knockout (KO) mice exhibit ejaculatory disorders, although they have normal sexual motivation. We hypothesized that mGluR7 regulates ejaculation by potentiating the excitability of the neural circuit in the lumbosacral spinal cord, because administration of the mGluR7-selective antagonist into that region inhibits drug-induced ejaculation. In the present study, to elucidate the mechanism of impaired ejaculation in mGluR7 KO mice, we eliminated the influence of the brain by spinal transection (spinalization). Unexpectedly, sexual responses of male mGluR7 KO mice were stronger than those of wild-type mice after spinalization. Histological examination indicated that mGluR7 controls sympathetic neurons as well as parasympathetic neurons. In view of the complexity of its synaptic regulation, mGluR7 might control ejaculation by multi-level and multi-modal mechanisms. Our study provides insight into the mechanism of ejaculation as well as a strategy for future therapies to treat ejaculatory disorders in humans.

Current and emerging treatment options for premature ejaculation

Premature ejaculation (PE) is a prevalent male sexual dysfunction. Current standard treatment regimens include behavioural therapies, topical anaesthetics, dapoxetine and other selective serotonin reuptake inhibitors (SSRIs). Most of the pharmacotherapeutic options target neurotransmitters (such as serotonin and oxytocin) that have a role in the ejaculation mechanism. However, these treatments are mildly effective and only provide a temporary delay in the ejaculation latency time, and PE recurs when the treatment is stopped. Thus, a treatment for PE is urgently needed and research is ongoing to find the ideal PE therapy. The efficacy and safety of topical anaesthetics and SSRIs in delaying ejaculation have been confirmed in many well-designed controlled trials. Both preclinical and clinical studies on new-generation SSRIs are ongoing. Moreover, promising results came from clinical trials in which the efficacy of on-demand PE therapies targeting neurotransmitters other than serotonin, such as α1-adrenoceptor antagonists and oxytocin antagonists, was assessed. Surgical intervention and neuromodulation have been proposed as potential treatment options for PE; however, current PE guidelines do not recommend these treatments owing to safety concerns.

Targeting bladder function with network-specific epidural stimulation after chronic spinal cord injury

Profound dysfunctional reorganization of spinal networks and extensive loss of functional continuity after spinal cord injury (SCI) has not precluded individuals from achieving coordinated voluntary activity and gaining multi-systemic autonomic control. Bladder function is enhanced by approaches, such as spinal cord epidural stimulation (scES) that modulates and strengthens spared circuitry, even in cases of clinically complete SCI. It is unknown whether scES parameters specifically configured for modulating the activity of the lower urinary tract (LUT) could improve both bladder storage and emptying. Functional bladder mapping studies, conducted during filling cystometry, identified specific scES parameters that improved bladder compliance, while maintaining stable blood pressure, and enabled the initiation of voiding in seven individuals with motor complete SCI. Using high-resolution magnetic resonance imaging and finite element modeling, specific neuroanatomical structures responsible for modulating bladder function were identified and plotted as heat maps. Data from this pilot clinical trial indicate that scES neuromodulation that targets bladder compliance reduces incidences of urinary incontinence and provides a means for mitigating autonomic dysreflexia associated with bladder distention. The ability to initiate voiding with targeted scES is a key step towards regaining volitional control of LUT function, advancing the application and adaptability of scES for autonomic function.

Neurons for Ejaculation and Factors Affecting Ejaculation

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.

Saporin as a Commercial Reagent: Its Uses and Unexpected Impacts in the Biological Sciences—Tools from the Plant Kingdom

Saporin is a ribosome-inactivating protein that can cause inhibition of protein synthesis and causes cell death when delivered inside a cell. Development of commercial Saporin results in a technology termed ‘molecular surgery’, with Saporin as the scalpel. Its low toxicity (it has no efficient method of cell entry) and sturdy structure make Saporin a safe and simple molecule for many purposes. The most popular applications use experimental molecules that deliver Saporin via an add-on targeting molecule. These add-ons come in several forms: peptides, protein ligands, antibodies, even DNA fragments that mimic cell-binding ligands. Cells that do not express the targeted cell surface marker will not be affected. This review will highlight some newer efforts and discuss significant and unexpected impacts on science that molecular surgery has yielded over the last almost four decades. There are remarkable changes in fields such as the Neurosciences with models for Alzheimer’s Disease and epilepsy, and game-changing effects in the study of pain and itch. Many other uses are also discussed to record the wide-reaching impact of Saporin in research and drug development.

Urethral pressure profile during ejaculation in men with spinal cord injury

Ejaculation is often impaired in men with spinal cord injury (SCI). The aim of this prospective study was to assess sequence of sphincteric events and ejaculation dyssynergia during penile vibratory stimulation (PVS) in SCI men. Simultaneous recordings of bladder, bladder neck, prostate and external urethral sphincter pressures were performed using a microtip catheter with 5 pressure transducers. Between 2017 and 2019, ten men participated in the study for a total of 17 procedures. Antegrade ejaculation was found in three men with upper motor neuron (UMN) lesion. Ejaculation was preceded by a progressive increase in all urethral pressures, reaching sustained (plateau) or intermittent peaks above 220 cm H₂0. Antegrade ejaculation occurred after intermittent decreases in pressure at the external urethral sphincter level down to 100 cm H₂0, while the pressure at the bladder neck remained high (up to or above 220 cm H₂0). PVS was ineffective in eliciting ejaculation in seven men. In the five patients with UMN lesions, PVS elicited an increase in the external urethral sphincter pressure (mean 51 cm H₂0), while there was no pressure change in the two patients with lower motor neuron lesions. Due to lack of enough retrograde retrieval attempts, the hypothesis of ejaculatory dyssynergia could not be verified.

Transcription factor gene Pea3 regulates erectile function during copulation in mice

Male mice with homozygous loss of function mutations of the transcription factor gene Pea3 (Pea3 null) are infertile due to their inability to inseminate females, however the specific deficits in male sexual behaviors that drive this phenotype are unknown. Here, the copulatory behavior of male mice (Pea3 null and control) with hormonally primed ovariectomized females was monitored via high-speed and high-resolution digital videography to assess for differences in female-directed social behaviors, gross sexual behaviors (mounting, thrusting), and erectile and ejaculatory function. Pea3 null male mice exhibit greatly reduced erectile function, with 44% of males displaying no visible erections during copulation, and 0% achieving sustained erections. As such, Pea3 null males are incapable of intromission and copulatory plug deposition, despite displaying largely normal female-directed social behaviors, mounting behaviors, and ejaculatory grasping behavior. Additionally, the organization and timing of thrusting behaviors is impaired in Pea3 null males. Our results show that the transcription factor gene Pea3 regulates the ability to achieve and maintain erections during copulation in mice.

What Is the Trigger for Sexual Climax?

A model is proposed to consider sexual climax in men, women, and animals as a unitary phenomenon. Sexual climax is a stereotyped rhythmic pattern of spinally generated neural activity in the autonomic and somatic nerves innervating pelvic organs. A column of neurons in the spinal cord of the male rat is strongly activated by ejaculation (sexual climax in the male). These neurons project to the thalamus and are therefore called lumbar spinothalamic cells (LSt cells). Comprehensive studies have demonstrated that the LSt cells constitute a central pattern generator of ejaculation. These findings have been extended to female animals. Further studies identified LSt cells in the lumbar spinal cord of men and women. Strong evidence indicates that the LSt cells mediate ejaculation in men. The climax model generalizes and extends these studies. It postulates that LSt cells in the lumbar spinal cord of humans and animals of both sexes generate climax. The LSt cells generate the neural activity driving the pelvic contractions and other responses of climax. The activity is transmitted to supraspinal sites to activate orgasm. The LSt cells receive excitatory and inhibitory projections from supraspinal sites. The descending projections reflect subjective arousal and inhibitions. Spinal sensory neurons from the genitals provide excitatory and inhibitory innervation to the LSt cells. These represent pleasurable and noxious sensations. The supraspinal and spinal excitatory and inhibitory inputs are integrated by the LSt. When the sum of the excitatory inputs, minus the sum of the inhibitory inputs reaches a threshold, the LSt cells generate sexual climax.

Sexual Experience Induces the Expression of Gastrin-Releasing Peptide and Oxytocin Receptors in the Spinal Ejaculation Generator in Rats

Male sexual function in mammals is controlled by the brain neural circuits and the spinal cord centers located in the lamina X of the lumbar spinal cord (L3–L4). Recently, we reported that hypothalamic oxytocin neurons project to the lumbar spinal cord to activate the neurons located in the dorsal lamina X of the lumbar spinal cord (dXL) via oxytocin receptors, thereby facilitating male sexual activity. Sexual experiences can influence male sexual activity in rats. However, how this experience affects the brain–spinal cord neural circuits underlying male sexual activity remains unknown. Focusing on dXL neurons that are innervated by hypothalamic oxytocinergic neurons controlling male sexual function, we examined whether sexual experience affects such neural circuits. We found that >50% of dXL neurons were activated in the first ejaculation group and ~30% in the control and intromission groups in sexually naïve males. In contrast, in sexually experienced males, ~50% of dXL neurons were activated in both the intromission and ejaculation groups, compared to ~30% in the control group. Furthermore, sexual experience induced expressions of gastrin-releasing peptide and oxytocin receptors in the lumbar spinal cord. This is the first demonstration of the effects of sexual experience on molecular expressions in the neural circuits controlling male sexual activity in the spinal cord.

Oxytocin, Erectile Function and Sexual Behavior: Last Discoveries and Possible Advances

A continuously increasing amount of research shows that oxytocin is involved in numerous central functions. Among the functions in which oxytocin is thought to be involved are those that play a role in social and sexual behaviors, and the involvement of central oxytocin in erectile function and sexual behavior was indeed one of the first to be discovered in laboratory animals in the 1980s. The first part of this review summarizes the results of studies done in laboratory animals that support a facilitatory role of oxytocin in male and female sexual behavior and reveal mechanisms through which this ancient neuropeptide participates in concert with other neurotransmitters and neuropeptides in this complex function, which is fundamental for the species reproduction. The second part summarizes the results of studies done mainly with intranasal oxytocin in men and women with the aim to translate the results found in laboratory animals to humans. Unexpectedly, the results of these studies do not appear to confirm the facilitatory role of oxytocin found in male and female sexual behavior in animals, both in men and women. Possible explanations for the failure of oxytocin to improve sexual behavior in men and women and strategies to attempt to overcome this impasse are considered.

Sexual Incentive Motivation and Copulatory Behavior in Male Rats Treated With the Adrenergic α2-Adrenoceptor Agonists Tasipimidine and Fadolmidine: Implications for Treatment of Premature Ejaculation

BACKGROUND

Premature ejaculation is the most common sexual dysfunction in young men, and it often leads to reduced relationship satisfaction and quality of life.

AIM

To determine the role of central and peripheral α₂-adrenoceptors in the control of ejaculation and sexual incentive motivation in rats.

METHODS

Sexual incentive motivation was studied in a large arena in which a male subject could choose between approaching and remaining close to a sexually receptive female or another male. Sexual behavior was studied in standard observation cages in which a male was allowed to freely interact with a receptive female for 30 minutes. Two highly selective agonists at the α₂-adrenoceptors, tasipimidine and fadolmidine, were administered before the tests. Low peripheral doses of fadolmidine have been reported to have effects mainly outside of the central nervous system, whereas at large doses also the central effects are evident.

OUTCOMES

The time spent close to the receptive female in relation to the time spent with the male and measures of ambulatory activity were obtained from the test for sexual incentive motivation, while the habitual parameters of sexual behavior were recorded with the copulation test.

RESULTS

Tasipimidine prolonged ejaculation latency and the interintromission interval at the dose of 200 µg/kg when data from fast-ejaculating rats were used. No other sexual parameter was modified. A dose of 100 µg/kg was ineffective. There was no consistent effect on sexual incentive motivation, although modest sedation was observed. Fadolmidine, a drug that does not easily penetrate the blood-brain barrier, had no effect on sexual incentive motivation at any of the doses used (3, 30, and 100 µg/kg). The largest dose had clear sedative effects. The lower doses had no systematic effect on sexual behavior, not even when only fast or very fast ejaculating males were analyzed.

CLINICAL TRANSLATION

The findings are relevant to the search for treatments for premature ejaculation that are specific enough to selectively delay ejaculation.

STRENGTHS & LIMITATIONS

The procedures used here are standard in the field and yield the most reliable data. Whether the effects observed in male rats are directly transferrable to men can only be determined through clinical studies.

CONCLUSION

The observation that drugs acting at central but not peripheral α₂-adrenoceptors prolong ejaculation latency without affecting any other parameter of sexual behavior or sexual incentive motivation suggests that this kind of drug may be suitable for treating premature ejaculation. Jyrki L., Elisa V.-A., Xi C., et al. Sexual Incentive Motivation and Copulatory Behavior in Male Rats Treated With the Adrenergic α₂-Adrenoceptor Agonists Tasipimidine and Fadolmidine: Implications for Treatment of Premature Ejaculation. J Sex Med 2021;18:1677-1689.

Ejaculatory dysfunction in men with diabetes mellitus

Diabetes mellitus (DM) is a metabolic disorder that is characterized by elevated blood glucose levels due to absolute or relative insulin deficiency, in the background of β-cell dysfunction, insulin resistance, or both. Such chronic hyperglycemia is linked to long-term damage to blood vessels, nerves, and various organs. Currently, the worldwide burden of DM and its complications is in increase. Male sexual dysfunction is one of the famous complications of DM, including abnormal orgasmic/ejaculatory functions, desire/libido, and erection. Ejaculatory dysfunction encompasses several disorders related to DM and its complications, such as premature ejaculation, anejaculation (AE), delayed ejaculation, retrograde ejaculation (RE), ejaculatory pain, anesthetic ejaculation, decreased ejaculate volume, and decreased force of ejaculation. The problems linked to ejaculatory dysfunction may extend beyond the poor quality of life in diabetics as both AE and RE are alleged to alter the fertility potential of these patients. However, although both diabetes patients and their physicians are increasingly aware of diabetic ejaculatory dysfunction, this awareness still lags behind that of other diabetes complications. Therefore, all these disorders should be looked for thoroughly during the clinical evaluation of diabetic men. Besides, introducing the suitable option and/or maneuvers to treat these disorders should be tailored according to each case. This review aimed to explore the most important findings regarding ejaculatory dysfunction in diabetes from pre-clinical and clinical perspectives.

Spinal Cord Injury Causes Reduction of Galanin and Gastrin Releasing Peptide mRNA Expression in the Spinal Ejaculation Generator of Male Rats

Spinal cord injury (SCI) in men is commonly associated with sexual dysfunction, including anejaculation, and chronic mid-thoracic contusion injury in male rats also impairs ejaculatory reflexes. Ejaculation is controlled by a spinal ejaculation generator consisting of a population of lumbar spinothalamic (LSt) neurons that control ejaculation through release of four neuropeptides including galanin and gastrin releasing peptide (GRP) onto lumbar and sacral autonomic and motor nuclei. It was recently demonstrated that spinal contusion injury in male rats caused reduction of GRP-immunoreactivity, but not galanin-immunoreactivity in LSt cells, indicative of reduced GRP peptide levels, but inconclusive results for galanin. The current study further tests the hypothesis that contusion injury causes a disruption of GRP and galanin mRNA in LSt cells. Male rats received mid-thoracic contusion injury and galanin and GRP mRNA were visualized 8 weeks later in the lumbar spinal cord using fluorescent in situ hybridization. Spinal cord injury significantly reduced GRP and galanin mRNA in LSt cells. Galanin expression was higher in LSt cells compared to GRP. However, expression of the two transcripts were positively correlated in LSt cells in both sham and SCI animals, suggesting that expression for the two neuropeptides may be co-regulated. Immunofluorescent visualization of galanin and GRP peptides demonstrated a significant reduction in GRP-immunoreactivity, but not galanin in LSt cells, confirming the previous observations. In conclusion, SCI reduced GRP and galanin expression in LSt cells with an apparent greater impact on GRP peptide levels. GRP and galanin are both essential for triggering ejaculation and thus such reduction may contribute to ejaculatory dysfunction following SCI in rats.

Systemic effects of oxytocin on male sexual activity via the spinal ejaculation generator in rats

Oxytocin is produced in the hypothalamus and stimulates uterine contraction and milk ejection. While many people consider oxytocin to be a female hormone, it is reported that, in men, the plasma oxytocin level increases markedly after ejaculation. However, this aspect of oxytocin physiology is poorly understood. The spinal ejaculation generator (SEG), which expresses the neuropeptide, gastrin-releasing peptide (GRP), can trigger ejaculation in rats. Therefore, we focused on systemic effects of oxytocin on the GRP/SEG neuron system in the lumbar spinal cord controlling sexual activity in male rats. We found that systemic administration of oxytocin significantly shortened the latency to the first mount, intromission and ejaculation during male copulatory behavior. In addition, the local oxytocin level in the lumbar cord was significantly higher in males than in females. Histological analysis showed that oxytocin-binding is apparent in spinal GRP/SEG neurons. We therefore conclude that oxytocin influences male sexual activity via the SEG.

In Vivo Electrophysiology of Peptidergic Neurons in Deep Layers of the Lumbar Spinal Cord after Optogenetic Stimulation of Hypothalamic Paraventricular Oxytocin Neurons in Rats

The spinal ejaculation generator (SEG) is located in the central gray (lamina X) of the rat lumbar spinal cord and plays a pivotal role in the ejaculatory reflex. We recently reported that SEG neurons express the oxytocin receptor and are activated by oxytocin projections from the paraventricular nucleus of hypothalamus (PVH). However, it is unknown whether the SEG responds to oxytocin in vivo. In this study, we analyzed the characteristics of the brain–spinal cord neural circuit that controls male sexual function using a newly developed in vivo electrophysiological technique. Optogenetic stimulation of the PVH of rats expressing channel rhodopsin under the oxytocin receptor promoter increased the spontaneous firing of most lamina X SEG neurons. This is the first demonstration of the in vivo electrical response from the deeper (lamina X) neurons in the spinal cord. Furthermore, we succeeded in the in vivo whole-cell recordings of lamina X neurons. In vivo whole-cell recordings may reveal the features of lamina X SEG neurons, including differences in neurotransmitters and response to stimulation. Taken together, these results suggest that in vivo electrophysiological stimulation can elucidate the neurophysiological response of a variety of spinal neurons during male sexual behavior.

Upregulated expression of NMDA receptor in the paraventricular nucleus shortens ejaculation latency in rats with experimental autoimmune prostatitis

BACKGROUND

Estimated 30%-40% of patients with chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS) suffer from premature ejaculation (PE), which is difficult to cure, but the mechanism is still unknown. Based on the results of our previous clinical studies and animal experiments, we propose that the glutamatergic system dysfunction in the paraventricular nucleus (PVN) may be involved.

METHODS

To test this hypothesis, we used experimental autoimmune prostatitis (EAP) rats to investigate the effects of CP/CPPS on ejaculation behavior through integrating copulatory behavior testing, neuroelectrophysiologic experiments, and molecular biology technologies.

RESULTS

Histological examination of prostate tissue in EAP rats exhibited consistent pathological findings with that in CP/CPPS patients. Behavior testing showed that ejaculation latency (EL) of EAP rats significantly shortened compared with the controls (5.1 ± 1.8 vs 9.1 ± 2.4 min, P < .001). Sympathetic nervous system (SNS) activity testing revealed that EAP rats displayed significantly higher plasma norepinephrine (NE) level (1780 ± 493 vs 1421 ± 453 pg/mL, P = .043) and SNS sensitivity (67.8 ± 9.6 vs 44.6 ± 8.7%, P < .001). Immunohistochemical detection and Western blot analysis both displayed that NR1 subunit expression of N-methyl-D-aspartic acid (NMDA) receptors in the PVN of EAP rats was significantly upregulated (P = .007 and P < .001). Furthermore, the expression of NMDA NR1 subunit positively correlated both with SNS sensitivity (r = .917, P < .001) and prostatic inflammation scores (r = .964, P < .001).

CONCLUSION

This study shows that EAP rats suffer from the same PE symptom as CP/CPPS patients. CP/CPPS-induced inflammatory-immune response can significantly upregulate the expression of NMDA receptors in the PVN, which shortening the EL by enhancing SNS sensitivity. However, the exact mechanism of chronic inflammation in the prostate causing the upregulated expression of NMDA receptors needs to be further studied.

Mapping of spinal interneurons involved in regulation of the lower urinary tract in juvenile male rats

Coordination between the urinary bladder (BL) and external urethral sphincter (EUS) is necessary for storage and elimination of urine. In rats interneuronal circuits at two levels of the spinal cord (i.e., L6-S1 and L3-L4) play an important role in this coordination. In the present experiments retrograde trans-synaptic transport of pseudorabies virus (PRV) encoding fluorescent markers (GFP and RFP) was used to trace these circuits. To examine the relative localization of EUS-related and BL-related interneuronal populations we injected PRV-GFP into the EUS and PRV-RFP into the BL wall. The PRV infected populations of spinal interneurons were localized primarily in the dorsal commissure (DCM) of L6/S1 and in a hypothesized lumbar spinal coordinating center (LSCC) in L3/L4 above and lateral to central canal (CC). At both sites colocalization of markers occurred in a substantial number of labeled interneurons indicating concomitant involvement of these double-labelled neurons in the EUS- and BL-circuits and suggesting their role in EUS-BL coordination. Intense GFP or RFP fluorescent was detected in a subpopulation of cells at both sites suggesting that they were infected earlier and therefore likely to represent first order, primary interneurons that directly synapse with output neurons. Larger numbers of weakly fluorescent neurons that likely represent second order interneurons were also identified. Within the population of EUS-related first order interneurons only 3-8 % exhibited positive immunoreaction for an early transcription factor Pax2 specific to GABAergic and glycinergic inhibitory neurons suggesting that the majority of interneurons in DCM and LSCC projecting directly to the EUS motoneurons are excitatory.

Spontaneous Ejaculation: A Focused Review for the Clinicians

INTRODUCTION

The process of ejaculation has important meanings not only for its association with orgasm but also for the timing to ejaculate in the context of sexual activity. Spontaneous (involuntary) ejaculation (SE) without any sexual stimulation is a distressing symptom. Our understanding of SE is limited. Unfortunately, many physicians are not aware of these cases.

OBJECTIVES

The objective of this study is to describe the etiopathogenesis, clinical features, diagnosis, and treatment options for SE.

METHODS

We searched the literature for publications on "SE," "spontaneous emission" or "involuntary ejaculation," and factors influencing SE in the PUBMED/MEDLINE, Scopus, Cochrane Library, EMBASE, PsycINFO, ProQuest, Academic Search Complete database, Google Scholar, and CINAHL databases from inception to August 2020.

RESULTS

The literature search yielded 36 relevant publications reporting on 43 patients with SE. Attempts to explain the cause of pathologic SE have included 4 etiological groups (spinal cord lesions, psychological causes, rabies, and drug-induced). The underlying mechanisms responsible for induction of SE may include increased adrenergic activity, overactivity in dopaminergic system, decreased serotonergic activity, damage of descending inhibitory pathway, or penile hyperexcitability. SE may occur in the absence of an identifiable trigger or may be triggered by non-sexual circumstances (micturition, defecation, glans touch, anxiety, panic attack, or school examinations). Treatment options include psychoanalytic treatment, paroxetine, citalopram, sertraline, silodosin, and anxiolytics. In drug-induced SE, dose reduction and drug withdrawal with or without switching to another drug may relief SE.

CONCLUSIONS

SE is one of the least reported ejaculatory dysfunction. The key feature shared in common by these men is SE without any sexual thoughts or fantasies, may be triggered by non-sexual contexts, rarely associated with orgasm or erection. Treatment by psychoanalytic treatment and pharmacotherapy may be helpful. Further research might explore the definite underlying mechanisms. Abdel-Hamid IA, Ali OI. Spontaneous Ejaculation: A Focused Review for the Clinicians. Sex Med Rev 2021;9:406-422.

Oxytocin Influences Male Sexual Activity via Non-synaptic Axonal Release in the Spinal Cord

Oxytocinergic neurons in the paraventricular nucleus of the hypothalamus that project to extrahypothalamic brain areas and the lumbar spinal cord play an important role in the control of erectile function and male sexual behavior in mammals. The gastrin-releasing peptide (GRP) system in the lumbosacral spinal cord is an important component of the neural circuits that control penile reflexes in rats, circuits that are commonly referred to as the "spinal ejaculation generator (SEG)." We have examined the functional interaction between the SEG neurons and the hypothalamo-spinal oxytocin system in rats. Here, we show that SEG/GRP neurons express oxytocin receptors and are activated by oxytocin during male sexual behavior. Intrathecal injection of oxytocin receptor antagonist not only attenuates ejaculation but also affects pre-ejaculatory behavior during normal sexual activity. Electron microscopy of potassium-stimulated acute slices of the lumbar cord showed that oxytocin-neurophysin-immunoreactivity was detected in large numbers of neurosecretory dense-cored vesicles, many of which are located close to the plasmalemma of axonal varicosities in which no electron-lucent microvesicles or synaptic membrane thickenings were visible. These results suggested that, in rats, release of oxytocin in the lumbar spinal cord is not limited to conventional synapses but occurs by exocytosis of the dense-cored vesicles from axonal varicosities and acts by diffusion-a localized volume transmission-to reach oxytocin receptors on GRP neurons and facilitate male sexual function.

Importance of neuroanatomical data from domestic animals to the development and testing of the KNDy hypothesis for GnRH pulse generation

Work during the last decade has led to a novel hypothesis for a question that is half a century old: how is the secretory activity of GnRH neurons synchronized to produce episodic GnRH secretion. This hypothesis posits that a group of neurons in the arcuate nucleus (ARC) that contain kisspeptin, neurokinin B (NKB), and dynorphin (known as KNDy neurons) fire simultaneously to drive each GnRH pulse. Kisspeptin is proposed to be the output signal to GnRH neurons with NKB and dynorphin acting within the KNDy network to initiate and terminate each pulse, respectively. This review will focus on the importance of neuroanatomical studies in general and, more specifically, on the work of Dr Marcel Amstalden during his postdoctoral fellowship with the authors, to the development and testing of this hypothesis. Critical studies in sheep that laid the foundation for much of the KNDy hypothesis included the report that a group of neurons in the ARC contain both NKB and dynorphin and appear to form an interconnected network capable of firing synchronously, and Marcel's observations that the NKB receptor is found in most KNDy neurons, but not in any GnRH neurons. Moreover, reports that almost all dynorphin-NKB neurons and kisspeptin neurons in the ARC contained steroid receptors led directly to their common identification as "KNDy" neurons. Subsequent anatomical work demonstrating that KNDy neurons project to GnRH somas and terminals, and that kisspeptin receptors are found in GnRH, but not KNDy neurons, provided important tests of this hypothesis. Recent work has explored the time course of dynorphin release onto KNDy neurons and has begun to apply new approaches to the issue, such as RNAscope in situ hybridization and the use of whole tissue optical clearing with light-sheet microscopy. Together with other approaches, these anatomical techniques will allow continued exploration of the functions of the KNDy population and the possible role of other ARC neurons in generation of GnRH pulses.

Metabotropic Glutamate Receptor Subtype 7 Is Essential for Ejaculation

Metabotropic glutamate receptor subtype 7 (mGluR7) is a member of the group III mGluRs, which are negatively coupled to adenylate cyclase via Gi/Go proteins and localized to presynaptic active zones of the mammalian central nervous system (CNS). To elucidate the mechanism of impaired reproductivity of mGluR7 knockout (KO) mice, we investigated sexual behavior in this line, which exhibits ejaculatory disorder, although with normal sexual motivation and erectile function. To identify the site of action within the CNS responsible for the effect of mGluR7 on ejaculation, we then used a para-chloroamphetamine (PCA)-induced ejaculation model. Intrathecal administration of the mGluR7-selective antagonist 6-(4-methoxyphenyl)-5-methyl-3-pyridin-4-ylisoxazolo[4,5-c]pyridin-4(5H)-one (MMPIP) into the lumbosacral spinal cord inhibited PCA-induced ejaculation. Immunohistochemistry revealed mGluR7-like immunoreactivity (LI) expressed in the same area where lumbar spinothalamic (LSt) cells regulate the parasympathetic ejaculatory pathway. At high magnification, the apposition of mGluR7-LI puncta and neuronal nitric oxide synthase (nNOS)-LI-positive putative parasympathetic preganglionic neurons was evident. These results indicate that mGluR7 in the lumbosacral spinal cord regulates ejaculation by potentiating the excitability of parasympathetic preganglionic neurons. The ejaculatory disorder is a major issue in the field of male reproductive function. Erectile dysfunction (ED) can be treated by phosphodiesterase type 5 inhibitors like sildenafil (Viagra®), but the ejaculatory disorder cannot. Lack of understanding of the ejaculatory mechanism hinders the development of therapies for ejaculatory problems. This study is the first to demonstrate that mGluR7 regulates ejaculation and the results provide insight into the mechanism of ejaculation as well as a strategy for future therapies to treat ejaculatory disorders in humans.

Spinal cord injury and diaphragm neuromotor control

Introduction: Neuromotor control of diaphragm muscle and the recovery of diaphragm activity following spinal cord injury have been narrowly focused on ventilation. By contrast, the understanding of neuromotor control for non-ventilatory expulsive/straining maneuvers (including coughing, defecation, and parturition) is relatively impoverished. This variety of behaviors are achieved via the recruitment of the diverse array of motor units that comprise the diaphragm muscle.Areas covered: The neuromotor control of ventilatory and non-ventilatory behaviors in health and in the context of spinal cord injury is explored. Particular attention is played to the neuroplasticity of phrenic motor neurons in various models of cervical spinal cord injury.Expert opinion: There is a remarkable paucity in our understanding of neuromotor control of maneuvers in spinal cord injury patients. Dysfunction of these expulsive/straining maneuvers reduces patient quality of life and contributes to severe morbidity and mortality. As spinal cord injury patient life expectancies continue to climb steadily, a nexus of spinal cord injury and age-associated comorbidities are likely to occur. While current research remains concerned only with the minutiae of ventilation, the major functional deficits of this clinical cohort will persist intractably. We posit some future research directions to avoid this scenario.

Lumbar spinal cord neurons putatively involved in ejaculation are sexually dimorphic in early postnatal mice

A crucial role in ejaculation is thought to be played by a population of lumbar spino-thalamic neurons (LSt), which express galanin and other neuropeptides. In rats, these neurons are activated with ejaculation and their lesion selectively abolishes ejaculation but not other mating behaviors. Consistently with their role, in adult rats and humans, LSt neurons are sexually dimorphic, being more numerous in males. Here we examined whether sexual dimorphism arises early in development, using a transgenic mouse line in which the expression of fluorescent protein is driven by the galanin promoter. We focused on postnatal day 4, shortly after a transient perinatal androgen surge in males that could play an organizational role in LSt development. We found a population of brightly fluorescent neurons organized in bilateral columns dorsolateral to the central canal in segments L1-L5, the expected location of the LSt group. Their number was close to that of adult preparations and significantly greater in male than in female siblings (+19%; CI_95% : +13% to +27%; p < .01). This was not due to a generalized higher galanin expression in the male since fluorescent L4 DRG neurons, innervating the hindlimbs and lower back, were not significantly dimorphic (-4%; CI_95% : -10% to +8%; p = .92). Unexpectedly, we found in cervical segments a population of fluorescent neurons having a location relative to the central canal similar to the LSt. Thus, the LSt group is sexually dimorphic soon after birth. However, it is possible that only a subset of its neurons participate in the control of ejaculation.

Two cases of psychogenic anejaculation patients got normal ejaculation ability after penile vibratory stimulation or electroejaculation

Psychogenic anejaculation is a unique problem which accounts for 0.4-0.5% of anejaculation patients. Although patients with this problem may experience erections and nocturnal emissions (NEs), they do not experience ejaculation during either masturbation or coitus. The etiology is presently unknown. Penile vibratory stimulation (PVS) and electroejaculation (EEJ) have been the main methods of sperm retrieval for psychogenic anejaculation couples undergoing assisted reproduction technology (ART). However, there is no special treatment which can heal psychogenic anejaculation patients. Here, we report two psychogenic anejaculation patients who recovered normal ejaculation ability after PVS or EEJ procedure.

Propriospinal Neurons of L3-L4 Segments Involved in Control of the Rat External Urethral Sphincter

Coordination of activity of external urethral sphincter (EUS) striated muscle and bladder (BL) smooth muscle is essential for efficient voiding. In this study we examined the morphological and electrophysiological properties of neurons in the L3/L4 spinal cord (SC) that are likely to have an important role in EUS-BL coordination in rats. EUS-related SC neurons were identified by retrograde transsynaptic tracing following injection of pseudorabies virus (PRV) co-expressing fluorescent markers into the EUS of P18-P20 male rats. Tracing revealed not only EUS motoneurons in L6/S1 but also interneurons in lamina X of the L6/S1 and L3/L4 SC. Physiological properties of fluorescently labeled neurons were assessed during whole-cell recordings in SC slices followed by reconstruction of biocytin-filled neurons. Reconstructions of neuronal processes from transverse or longitudinal slices showed that some L3/L4 neurons have axons projecting toward and into the ventro-medial funiculus (VMf) where axons extended caudally. Other neurons had axons projecting within laminae X and VII. Dendrites of L3/L4 neurons were distributed within laminae X and VII. The majority of L3/L4 neurons exhibited tonic firing in response to depolarizing currents. In transverse slices focal electrical stimulation (FES) in the VMf or in laminae X and VII elicited antidromic axonal spikes and/or excitatory synaptic responses in L3/L4 neurons; while in longitudinal slices FES elicited excitatory synaptic inputs from sites up to 400 μm along the central canal. Inhibitory inputs were rarely observed. These data suggest that L3/L4 EUS-related circuitry consists of at least two neuronal populations: segmental interneurons and propriospinal neurons projecting to L6/S1.

Cligosiban, A Novel Brain-Penetrant, Selective Oxytocin Receptor Antagonist, Inhibits Ejaculatory Physiology in Rodents

INTRODUCTION

Few treatments are available for men with premature ejaculation (PE); oxytocin (OT) receptor antagonism in the central nervous system (CNS) is a potential new approach.

AIM

To determine if cligosiban selectively inhibits human OT receptors, penetrates the CNS, shows pharmacology in the CNS, and effects ejaculatory physiology in pre-clinical systems.

METHODS

Experiments complied with United Kingdom legislation and were subject to local ethical review. In vitro potency and selectivity of cligosiban was assessed using recombinant and native OT receptor systems including both neuronal and non-neuronal cell types. Selectivity was determined over neighboring V_1A, V_1B, and V₂ vasopressin receptors using a combination of recombinant and native vasopressin receptor assay systems. To determine an effect on central OT receptors and on ejaculation, cligosiban was evaluated in 2 anesthetized rat models-the electromyography model of ejaculatory physiology and a model of OT-mediated CNS neuronal firing. The CNS penetration of cligosiban was also determined by measuring cerebrospinal fluid and plasma drug concentrations following an intravenous (IV) infusion in rats.

MAIN OUTCOME MEASURE

These were functional measures of pharmacology in vitro, in cell lines and tissues, and in vivo in rats.

RESULTS

Cligosiban is a potent OT receptor antagonist, with a base dissociation constant of 5.7 nmol/L against native human uterine smooth muscle cell OT receptors. Cligosiban displays similar antagonistic potency against human recombinant and rat native OT receptors, including neuronal OT receptors. Cligosiban demonstrates >100-fold selectivity over human V_1A, V_1B, and V₂ vasopressin receptors. In the electromyography model, cligosiban (0.9 mg/kg, IV bolus) reduced the bulbospongiosum burst pattern and contraction amplitude associated with ejaculation. In the anesthetized CNS neuronal firing model, the same dosing regimen of cligosiban (0.9 mg/kg IV bolus) modulated the OT-mediated response in the nucleus tractus solitarius. After systemic dosing to rats, cligosiban showed good CNS penetration.

CLINICAL IMPLICATIONS

As the first highly selective and centrally penetrant OT receptor antagonist, cligosiban represents a promising compound to test the clinical hypothesis that antagonism of central OT receptors may be of therapeutic benefit in the treatment of PE.

STRENGTH & LIMITATIONS

The pharmacology and selectivity of cligosiban is determined using functional assays in recombinant cell lines, native cell lines, and tissue. Functional outcomes in in vivo systems are linked to CNS measures of pharmacology. The translation of the animal models of ejaculation to PE in man is unproven.

CONCLUSION

Cligosiban, a potent, selective OT receptor antagonist, demonstrated CNS penetration and pharmacology and, using the same dosing regimen, inhibited apomorphine-induced ejaculation in rats. Cligosiban is a promising compound to test the clinical hypothesis that antagonism of central OT receptors may be of therapeutic benefit in the treatment of PE. Wayman C, Russell R, Tang K, et al. Cligosiban, A Novel Brain Penetrant Selective Oxytocin Receptor Antagonist, Inhibits Ejaculatory Physiology in Rodents. J Sex Med 2018;15:1698-1706.

Premature Ejaculation: Aetiology and Treatment Strategies

Premature ejaculation (PE) is a highly prevalent male sexual dysfunction that is often neglected, presenting a currently unmet therapeutic need. The classification of PE has historically been varied and at times ambiguous, contributing to inaccurate prevalence estimates. This review uses the International Society for Sexual Medicine (ISSM) definition of PE, which includes reduced ejaculatory latency, lack of control and associated negative personal consequences. Patient assessment and management options differ depending on the classification of PE and it is the role of the clinician to appropriately classify patients and be aware of the correct management strategies. This review provides an overall background of PE in terms of classification and underlying physiology, patient assessment and management strategies along with the scientific rationale for treatment. Patients with lifelong and acquired PE are most likely to benefit from combination therapy of pharmacological treatment in the form of selective serotonin re-uptake inhibitor dapoxetine, psychosexual behavioural therapy and psychological therapy.

Central pattern generators in the brainstem and spinal cord: an overview of basic principles, similarities and differences

Central pattern generators (CPGs) are generally defined as networks of neurons capable of enabling the production of central commands, specifically controlling stereotyped, rhythmic motor behaviors. Several CPGs localized in brainstem and spinal cord areas have been shown to underlie the expression of complex behaviors such as deglutition, mastication, respiration, defecation, micturition, ejaculation, and locomotion. Their pivotal roles have clearly been demonstrated although their organization and cellular properties remain incompletely characterized. In recent years, insightful findings about CPGs have been made mainly because (1) several complementary animal models were developed; (2) these models enabled a wide variety of techniques to be used and, hence, a plethora of characteristics to be discovered; and (3) organizations, functions, and cell properties across all models and species studied thus far were generally found to be well-preserved phylogenetically. This article aims at providing an overview for non-experts of the most important findings made on CPGs in in vivo animal models, in vitro preparations from invertebrate and vertebrate species as well as in primates. Data about CPG functions, adaptation, organization, and cellular properties will be summarized with a special attention paid to the network for locomotion given its advanced level of characterization compared with some of the other CPGs. Similarities and differences between these networks will also be highlighted.

Chronic Spinal Cord Injury Reduces Gastrin-Releasing Peptide in the Spinal Ejaculation Generator in Male Rats

Spinal cord injury (SCI) causes sexual dysfunction, including anejaculation in men. Likewise, chronic mid-thoracic contusion injury impairs ejaculatory reflexes in male rats. Ejaculation is controlled by a spinal ejaculation generator (SEG) comprised of a population of lumbar spinothalamic (LSt) neurons. LSt neurons co-express four neuropeptides, including gastrin-releasing peptide (GRP) and galanin and control ejaculation via release of these peptides in lumbar and sacral autonomic and motor nuclei. Here, we tested the hypothesis that contusion injury causes a disruption of the neuropeptides that are expressed in LSt cell bodies and axon terminals, thereby causing ejaculatory dysfunction. Male Sprague Dawley rats received contusion or sham surgery at spinal levels T6-7. Five to six weeks later, animals were perfused and spinal cords were immunoprocessed for galanin and GRP. Results showed that numbers of cells immunoreactive for galanin were not altered by SCI, suggesting that LSt cells are not ablated by SCI. In contrast, GRP immunoreactivity was decreased in LSt cells following SCI, evidenced by fewer GRP and galanin/GRP dual labeled cells. However, SCI did not affect efferent connections of LSt, cells as axon terminals containing galanin or GRP in contact with autonomic cells were not reduced following SCI. Finally, no changes in testosterone plasma levels or androgen receptor expression were noted after SCI. In conclusion, chronic contusion injury decreased immunoreactivity for GRP in LSt cell soma, but did not affect LSt neurons per se or LSt connections within the SEG. Since GRP is essential for triggering ejaculation, such loss may contribute to ejaculatory dysfunction following SCI.

Comparison of the levels of the serotonin metabolite, 5-hydroxyindole acetic acid, in cerebrospinal fluid from patients with and without premature ejaculation

INTRODUCTION

Premature ejaculation (PE) is a significant problem as it can cause a loss of sexual self-confidence and a significant deterioration in quality of life. The frequency of PE varies between 9% and 27%. In the current study, we aimed to compare the levels of the serotonin metabolite 5HIAA (5 hydroxyindole acetic acid) in the cerebrospinal fluid (CSF) of patients with and without PE according to IELT (intravaginal ejaculation latency time) in order to investigate the relationship of PE with CSF 5HIAA levels.

MATERIALS AND METHODS

A total of 60 male patients were included in the study who were planning to undergo surgery under spinal anesthesia, 30 in the patient (PE) group (all of the included patients had an IELT of <1min) and 30 in the control group (patients had an IELT of >1min). Levels of CSF 5HIAA were measured.

RESULTS

There was a significant negative correlation between IELT and the 5HIAA variables in all patients (r=-0.322, p=0.012). Although the average 5HIAA levels (nmol/L) were higher in the patient group (86.80±28.33) than in the control group (76.44±35.91), this difference was not significant (p=0.22).

DISCUSSION

Results of the current study bring new and different perspectives to the explanation of PE pathophysiology. There is a need for more specific and genetic studies to determine the best treatment for this common disorder.

Evolution and Functional Differentiation of the Diaphragm Muscle of Mammals

Symmorphosis is a concept of economy of biological design, whereby structural properties are matched to functional demands. According to symmorphosis, biological structures are never over designed to exceed functional demands. Based on this concept, the evolution of the diaphragm muscle (DIAm) in mammals is a tale of two structures, a membrane that separates and partitions the primitive coelomic cavity into separate abdominal and thoracic cavities and a muscle that serves as a pump to generate intra-abdominal (Pab ) and intrathoracic (Pth ) pressures. The DIAm partition evolved in reptiles from folds of the pleural and peritoneal membranes that was driven by the biological advantage of separating organs in the larger coelomic cavity into separate thoracic and abdominal cavities, especially with the evolution of aspiration breathing. The DIAm pump evolved from the advantage afforded by more effective generation of both a negative Pth for ventilation of the lungs and a positive Pab for venous return of blood to the heart and expulsive behaviors such as airway clearance, defecation, micturition, and child birth. © 2019 American Physiological Society. Compr Physiol 9:715-766, 2019.

Hormone-dependent medial preoptic/lumbar spinal cord/autonomic coordination supporting male sexual behaviors

Testosterone (T) can act directly through neural androgen receptors (AR) to facilitate male sexual behavior; however, T's metabolites also can play complicated and interesting roles in the control of mating. One metabolite, dihydrotestosterone (DHT) binds to AR with significantly greater affinity than that of T. Is that important behaviorally? Another metabolite, estradiol (E), offers a potential alternative route of facilitating male mating behavior by acting through estradiol receptors (ER). In this review we explore the roles and relative importance of T as well as E and DHT at various levels of the neuroaxis for the activation of male sex behavior in common laboratory animals and, when relevant research findings are available, in man.