Dopamine–oxytocin interactions in penile erection

A novel reuptake inhibitor, IP2015, induces erection by increasing central dopamine and peripheral nitric oxide release

BACKGROUND AND PURPOSE

An estimated 40% of patients with erectile dysfunction have a poor prognosis for improvement with currently available treatments. The present study investigated whether a newly developed monoamine transport inhibitor, IP2015, improves erectile function.

EXPERIMENTAL APPROACH

We investigated the effects of IP2015 on monoamine uptake and binding, erectile function in rats and diabetic mice and the effect on corpus cavernosum contractility.

KEY RESULTS

IP2015 inhibited the uptake of 5-HT, noradrenaline and dopamine by human monoamine transporters expressed in cells and in rat brain synaptosomes. Intracavernosal pressure measurement in anaesthetized rats revealed that IP2015 dose-dependently increased the number and the duration of spontaneous erections. Whereas pretreatment with the dopamine D2-like receptor antagonists, clozapine and (-)-sulpiride, or cutting the cavernosal nerve inhibited IP2015-induced erectile responses, the phosphodiesterase type 5 inhibitor sildenafil further enhanced the IP2015-mediated increase in intracavernosal pressure. IP2015 also increased the number of erections in type 2 diabetic db/db mice. Direct intracavernosal injection of IP2015 increased penile pressure, and in corpus cavernosum strips, IP2015 induced concentration-dependent relaxations. These relaxations were enhanced by sildenafil and blunted by endothelial cell removal, a nitric oxide synthase inhibitor, NG-nitro-l-arginine and a D1-like receptor antagonist, SCH23390. Quantitative polymerase chain reaction (qPCR) showed the expression of the dopamine transporter in the rat corpus cavernosum.

CONCLUSION AND IMPLICATIONS

Our findings suggest that IP2015 stimulates erectile function by a central mechanism involving dopamine reuptake inhibition and direct NO-mediated relaxation of the erectile tissue. This novel multi-modal mechanism of action could offer a new treatment approach to erectile dysfunction.

Convergence of oxytocin and dopamine signalling in neuronal circuits: Insights into the neurobiology of social interactions across species

Social behaviour is essential for animal survival, and the hypothalamic neuropeptide oxytocin (OXT) critically impacts bonding, parenting, and decision-making. Dopamine (DA), is released by ventral tegmental area (VTA) dopaminergic neurons, regulating social cues in the mesolimbic system. Despite extensive exploration of OXT and DA roles in social behaviour independently, limited studies investigate their interplay. This narrative review integrates insights from human and animal studies, particularly rodents, emphasising recent research on pharmacological manipulations of OXT or DA systems in social behaviour. Additionally, we review studies correlating social behaviour with blood/cerebral OXT and DA levels. Behavioural facets include sociability, cooperation, pair bonding and parental care. In addition, we provide insights into OXT-DA interplay in animal models of social stress, autism, and schizophrenia. Emphasis is placed on the complex relationship between the OXT and DA systems and their collective influence on social behaviour across physiological and pathological conditions. Understanding OXT and DA imbalance is fundamental for unravelling the neurobiological underpinnings of social interaction and reward processing deficits observed in psychiatric conditions.

The role of intraamygdaloid oxytocin in spatial learning and avoidance learning

The goal of the present study is to investigate the role of intraamygdaloid oxytocin in learning-related mechanisms. Oxytocin is a neuropeptide which is involved in social bonding, trust, emotional responses and various social behaviors. By conducting passive avoidance and Morris water maze tests on male Wistar rats, the role of intraamygdaloid oxytocin in memory performance and learning was investigated. Oxytocin doses of 10 ng and 100 ng were injected into the central nucleus of the amygdala. Our results showed that 10 ng oxytocin significantly reduced the time required to locate the platform during the Morris water maze test while significantly increasing the latency time in the passive avoidance test. However, the 100 ng oxytocin experiment failed to produce a significant effect in either of the tests. Wistar rats pretreated with 20 ng oxytocin receptor antagonist (L-2540) were administered 10 ng of oxytocin into the central nucleus of the amygdala and were also subjected to the aforementioned tests to highlight the role of oxytocin receptors in spatial- and avoidance learning. Results suggest that oxytocin supports memory processing during both the passive avoidance and the Morris water maze tests. Oxytocin antagonists can however block the effects of oxytocin in both tests. The results substantiate that oxytocin uses oxytocin receptors to enhance memory and learning performance.

Intraamygdaloid Oxytocin Increases Time Spent on Social Interaction in Valproate-Induced Autism Animal Model

Autism spectrum disorder (ASD) is a pervasive neurodevelopmental disorder that affects about 1.5% of children worldwide. One of the core symptoms is impaired social interaction. Since proper treatment has not been found yet, an investigation of the exact pathophysiology of autism is essential. The valproate (VPA)-induced rat model can be an appropriate way to study autism. Oxytocin (OT) may amend some symptoms of ASD since it plays a key role in developing social relationships. In the present study, we investigated the effect of the intraamygdaloid OT on sham and intrauterine VPA-treated rats' social interaction using Crawley's social interaction test. Bilateral guide cannulae were implanted above the central nucleus of the amygdala (CeA), and intraamygdaloid microinjections were carried out before the test. Our results show that male Wistar rats prenatally exposed to VPA spent significantly less time on social interaction. Bilateral OT microinjection increased the time spent in the social zone; it also reached the level of sham-control animals. OT receptor antagonist blocked this effect of the OT but in itself did not significantly influence the behavior of the rats. Based on our results, we can establish that intraamygdaloid OT has significantly increased time spent on social interaction in the VPA-induced autism model, and its effect is receptor-specific.

Effect of Neurosteroids on Basal and Stress-Induced Oxytocin Secretion in Luteal-Phase and Pregnant Sheep

Oxytocin (OT) is a neuropeptide synthesized in the hypothalamic nuclei that modulates both behavioral and reproductive functions, associated with the increased neurosteroid synthesis in the brain. Therefore, the present study tested the hypothesis that manipulation of central neurosteroid levels could affect oxytocin synthesis and release in non-pregnant and pregnant sheep under both basal and stressful conditions. In Experiment 1, luteal-phase sheep were subjected to a series of intracerebroventricular (icv.) infusions of allopregnanolone (AL, 4 × 15 μg/60 μL/30 min) for 3 days. In Experiment 2, pregnant animals (4th month) received a series of infusions of the neurosteroid synthesis blocker, finasteride (4 × 25 μg/60 μL/30 min), conducted for 3 days. In non-pregnant sheep AL alone was shown to differentially modulate OT synthesis in basal conditions, and strongly inhibit OT response to stress (p < 0.001). In contrast, in pregnant animals, basal and stress-induced OT secretion was significantly (p < 0.001) increased during finasteride infusion compared to controls. In conclusion, we showed that neurosteroids were involved in the control of OT secretion in sheep, particularly under stress and pregnancy conditions and are part of an adaptive mechanism which is responsible for protecting and maintaining pregnancy in harmful situations.

Erectile Dysfunction: Treatments, Advances and New Therapeutic Strategies

Erectile dysfunction (ED) is the inability to get and maintain an adequate penile erection for satisfactory sexual intercourse. Due to its negative impacts on men's life quality and increase during aging (40% of men between 40 and 70 years), ED has always attracted researchers of different disciplines, from urology, andrology and neuropharmacology to regenerative medicine, and vascular and prosthesis implant surgery. Locally and/or centrally acting drugs are used to treat ED, e.g., phosphodiesterase 5 inhibitors (first in the list) given orally, and phentolamine, prostaglandin E1 and papaverine injected intracavernously. Preclinical data also show that dopamine D4 receptor agonists, oxytocin and α-MSH analogues may have a role in ED treatment. However, since pro-erectile drugs are given on demand and are not always efficacious, new strategies are being tested for long lasting cures of ED. These include regenerative therapies, e.g., stem cells, plasma-enriched platelets and extracorporeal shock wave treatments to cure damaged erectile tissues. Although fascinating, these therapies are laborious, expensive and not easily reproducible. This leaves old vacuum erection devices and penile prostheses as the only way to get an artificial erection and sexual intercourse with intractable ED, with penile prosthesis used only by accurately selected patients.

Courses of Arginine-Vasopressin in the Systemic and Cavernous Blood through Different Stages of Sexual Arousal in Healthy Males and Patients with Erectile Dysfunction

To investigate the role of the peptide arginine-vasopressin (AVP) in controlling the function of penile erectile tissue, we determined the course of AVP through different stages of sexual arousal in both the systemic and cavernous blood of healthy males and patients presenting with ED. Twenty-five healthy males and 45 patients with ED were exposed to erotic stimulation to induce sexual arousal. Blood was withdrawn from the corpus cavernosum and a cubital vein during penile flaccidity, tumescence, rigid erection (attained only by the healthy individuals), and detumescence. AVP (ng/l plasma) was determined by means of a radioimmunoassay. Effects of AVP (0.1 to 100 nM) on isolated human CC were examined using a tissue bath system. AVP elicited contraction of isolated CC. In the healthy subjects, a decline in AVP levels (5.4 to 3 ng/l) was seen in the systemic blood when the flaccid penis became rigid. In the cavernous blood, no alterations were registered. In the group of ED patients, AVP in the systemic circulation did not display a transient decline. The drop in systemic AVP in healthy males during sexual stimulation might be a prerequisite to enable penile erection.

Intranasal oxytocin attenuates the effects of monetary feedback on procedural learning

Procedural learning is a vital brain function that allows us to acquire motor skills during development or re-learn them after lesions affecting the motor system. Procedural learning can be improved by feedback of different valence, e.g., monetary or social, mediated by dopaminergic circuits. While processing motivationally relevant stimuli, dopamine interacts closely with oxytocin, whose effects on procedural learning, particularly feedback-based approaches, remain poorly understood. In a randomized, double-blind, placebo-controlled trial, we investigated whether oxytocin modulates the differential effects of monetary and social feedback on procedural learning. Sixty-one healthy male participants were randomized to receive a placebo or oxytocin intranasally. The participants then performed a modified serial reaction time task. Oxytocin plasma concentrations were measured before and after applying the placebo or verum. Groups did not differ regarding general reaction times or measures of procedural learning. For the placebo group, monetary feedback improved procedural learning compared to a neutral control condition. In contrast, the oxytocin group did not show a differential effect of monetary or social feedback despite a significant increase in oxytocin plasma levels after intranasal application. The data suggest that oxytocin does not influence procedural learning per se. Instead, oxytocin seems to attenuate the effects of monetary feedback on procedural learning specifically.

Oxytocin receptor expression patterns in the human brain across development

Oxytocin plays a vital role in social behavior and homeostatic processes, with animal models indicating that oxytocin receptor (OXTR) expression patterns in the brain influence behavior and physiology. However, the developmental trajectory of OXTR gene expression is unclear. By analyzing gene expression data in human post-mortem brain samples, from the prenatal period to late adulthood, we demonstrate distinct patterns of OXTR gene expression in the developing brain, with increasing OXTR expression along the course of the prenatal period culminating in a peak during early childhood. This early life OXTR expression peak pattern appears slightly earlier in a comparative macaque sample, which is consistent with the relative immaturity of the human brain during early life compared to macaques. We also show that a network of genes with strong spatiotemporal couplings with OXTR is enriched in several psychiatric illness and body composition phenotypes. Taken together, these results demonstrate that oxytocin signaling plays an important role in a diverse set of psychological and somatic processes across the lifespan.

Dopamine, Erectile Function and Male Sexual Behavior from the Past to the Present: A Review

Early and recent studies show that dopamine through its neuronal systems and receptor subtypes plays different roles in the control of male sexual behavior. These studies show that (i) the mesolimbic/mesocortical dopaminergic system plays a key role in the preparatory phase of sexual behavior, e.g., in sexual arousal, motivation and reward, whereas the nigrostriatal system controls the sensory-motor coordination necessary for copulation, (ii) the incertohypothalamic system is involved in the consummatory aspects of sexual behavior (penile erection and copulation), but evidence for its role in sexual motivation is also available, (iii) the pro-sexual effects of dopamine occur in concert with neural systems interconnecting the hypothalamus and preoptic area with the spinal cord, ventral tegmental area and other limbic brain areas and (iv) D₂ and D₄ receptors play a major role in the pro-sexual effects of dopamine. Despite some controversy, increases or decreases, respectively, of brain dopamine activity induced by drugs or that occur physiologically, usually improves or worsens, respectively, sexual activity. These findings suggest that an altered central dopaminergic tone plays a role in mental pathologies characterized by aberrant sexual behavior, and that pro-erectile D₄ receptor agonists may be considered a new strategy for the treatment of erectile dysfunction in men.

Neurobiology of Loneliness, Isolation, and Loss: Integrating Human and Animal Perspectives

In social species such as humans, non-human primates, and even many rodent species, social interaction and the maintenance of social bonds are necessary for mental and physical health and wellbeing. In humans, perceived isolation, or loneliness, is not only characterized by physical isolation from peers or loved ones, but also involves negative perceptions about social interactions and connectedness that reinforce the feelings of isolation and anxiety. As a complex behavioral state, it is no surprise that loneliness and isolation are associated with dysfunction within the ventral striatum and the limbic system - brain regions that regulate motivation and stress responsiveness, respectively. Accompanying these neural changes are physiological symptoms such as increased plasma and urinary cortisol levels and an increase in stress responsivity. Although studies using animal models are not perfectly analogous to the uniquely human state of loneliness, studies on the effects of social isolation in animals have observed similar physiological symptoms such as increased corticosterone, the rodent analog to human cortisol, and also display altered motivation, increased stress responsiveness, and dysregulation of the mesocortical dopamine and limbic systems. This review will discuss behavioral and neuropsychological components of loneliness in humans, social isolation in rodent models, and the neurochemical regulators of these behavioral phenotypes with a neuroanatomical focus on the corticostriatal and limbic systems. We will also discuss social loss as a unique form of social isolation, and the consequences of bond disruption on stress-related behavior and neurophysiology.

Erectile Function and Sexual Behavior: A Review of the Role of Nitric Oxide in the Central Nervous System

Nitric oxide (NO), the neuromodulator/neurotransmitter formed from l-arginine by neuronal, endothelial and inducible NO synthases, is involved in numerous functions across the body, from the control of arterial blood pressure to penile erection, and at central level from energy homeostasis regulation to memory, learning and sexual behavior. The aim of this work is to review earlier studies showing that NO plays a role in erectile function and sexual behavior in the hypothalamus and its paraventricular nucleus and the medial preoptic area, and integrate these findings with those of recent studies on this matter. This revisitation shows that NO influences erectile function and sexual behavior in males and females by acting not only in the paraventricular nucleus and medial preoptic area but also in extrahypothalamic brain areas, often with different mechanisms. Most importantly, since these areas are strictly interconnected with the paraventricular nucleus and medial preoptic area, send to and receive neural projections from the spinal cord, in which sexual communication between brain and genital apparatus takes place, this review reveals that central NO participates in concert with neurotransmitters/neuropeptides to a neural circuit controlling both the consummatory (penile erection, copulation, lordosis) and appetitive components (sexual motivation, arousal, reward) of sexual behavior.

The interplay between glutamatergic circuits and oxytocin neurons in the hypothalamus and its relevance to neurodevelopmental disorders

Oxytocin (OXT) neurons of the hypothalamus are at the center of several physiological functions, including milk ejection, uterus contraction, and maternal and social behavior. In lactating females, OXT neurons show a pattern of burst firing and inter-neuron synchronization during suckling that leads to pulsatile release of surges of OXT into the bloodstream to stimulate milk ejection. This pattern of firing and population synchronization may be facilitated in part by hypothalamic glutamatergic circuits, as has been observed in vitro using brain slices obtained from male rats and neonates. However, it remains unknown how hypothalamic glutamatergic circuits influence OXT cell activity outside the context of lactation. In this review, we summarize the in vivo and in vitro studies that describe the synchronized burst firing pattern of OXT neurons and the implication of hypothalamic glutamate in this pattern of firing. We also make note of the few studies that have traced glutamatergic afferents to the hypothalamic paraventricular and supraoptic nuclei. Finally, we discuss the genetic findings implicating several glutamatergic genes in neurodevelopmental disorders, including autism spectrum disorder, thus underscoring the need for future studies to investigate the impact of these mutations on hypothalamic glutamatergic circuits and the OXT system.

Enhanced D2 Agonism Induces Conditioned Appetitive Sexual Responses Toward Non-reproductive Conspecifics

Brain mechanisms of sexual attraction toward reproductive partners develop from a systematic interrelationship between biology (nature) and learning (nurture). However, the causes of attraction toward non-reproductive partners are poorly understood. Here, we explored the role of Pavlovian learning under dopaminergic agonism on the development of sexual preference and brain activation for young male rats. During conditioning, adult sexually naïve males received either Saline (Saline-Paired) or the D2-receptor agonist quinpirole (QNP-Paired) and cohabited in contingency, or out of contingency (QNP-Unpaired) during 24 h with an almond-scented prepubertal juvenile male (PD25). Conditioning occurred every 4 days for three trials. Social and sexual responses were assessed four days after the last conditioning trial in a drug-free test, and males chose freely between a scented young male (PD37) and a novel receptive female. Four days later, males were exposed to the conditioned odor only and brain Fos-IR and serum testosterone were analyzed. Saline-Paired and QNP-Unpaired males displayed more non-contact erections (NCEs) and genital investigations for females, whereas QNP-Paired males expressed more NCEs and genital investigations for young males. In the QNP-Paired group, exposure to the young male-paired odor evoked more Fos-IR in limbic, hypothalamic and cortical areas, but no differences in serum testosterone were observed. Cohabitation with juvenile males during enhanced D2 agonism results in atypical appetitive sexual responses and a higher pattern of brain response for the young male-paired odor, with no changes in serum testosterone. We discuss the potential implications for the development of pedophilic disorder and perhaps other paraphilias.

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.

Disturbance of the reciprocal-interaction between the OXTergic and DAergic systems in the CNS causes atypical social behavior in syntaxin 1A knockout mice

Several studies have shown that oxytocin (OXT) modulates social behavior. Similarly, monoamines such as dopamine (DA) play a role in regulating social behavior. Previous studies have demonstrated that the soluble N-ethylmaleimide-sensitive fusion attachment protein receptor (SNARE) protein syntaxin 1A (STX1A) regulates the secretion of OXT and monoamines, and that STX1A gene knockout (STX1A KO) mice exhibit atypical social behavior, such as deficient social recognition, due to reduced OXT release. In this study, we analyzed the neural mechanism regulating social behavior by OXT and/or DA using STX1A KO mice as a model animal. We found that OXT directly induced DA release from cultured DA neurons through OXT and V1a receptors. In STX1A KO mice, the atypical social behavior was partially improved by OXT administration, which was inhibited by D1 receptor blockade. In addition, the atypical social behavior in STX1A KO mice was partially improved by facilitation of DAergic signaling with the DA reuptake inhibitor GBR12909. Moreover, the amelioration by GBR12909 was inhibited by OXTR blockade. These results suggest that the reciprocal interaction between the DAergic and OXTergic neuronal systems in the CNS may be important in regulating social behavior.

Oxytocin and Addiction: Potential Glutamatergic Mechanisms

Recently, oxytocin (OXT) has been investigated for its potential therapeutic role in addiction. OXT has been found to diminish various drug-seeking and drug-induced behaviors. Although its behavioral effects are well-established, there is not much consensus on how this neuropeptide exerts its effects. Previous research has given thought to how dopamine (DA) may be involved in oxytocinergic mechanisms, but there has not been as strong of a focus on the role that glutamate (Glu) has. The glutamatergic system is critical for the processing of rewards and the disruption of glutamatergic projections produces the behaviors seen in drug addicts. We introduce the idea that OXT has direct effects on Glu transmission within the reward processing pathway. Thus, OXT may reduce addictive behaviors by restoring abnormal drug-induced changes in the glutamatergic system and in its interactions with other neurotransmitters. This review offers insight into the mechanisms through which a potentially viable therapeutic target, OXT, could be used to reduce addiction-related behaviors.

Oxytocin signaling in the treatment of drug addiction: Therapeutic opportunities and challenges

Drug addiction is one of the leading causes of mortality worldwide. Despite great advances were achieved in understanding the neurobiology of drug addiction, the therapeutic options are severely limited, with poor effectiveness and serious side effects. The neuropeptide oxytocin (OXT) is well known for its effects on uterine contraction, sexual/maternal behaviors, social affiliation, stress and learning/memory by interacting with the OXT receptor and other neuromodulators. Emerging evidence suggests that the acute or chronic exposure to drugs can affect the OXT system. Additionally, OXT administration can ameliorate a wide range of abused drug-induced neurobehavioral changes. Overall, OXT not only suppresses drug reward in the binge stage of drug addiction, but also reduces stress responses and social impairments during the withdrawal stage and, finally, prevents drug/cue/stress-induced reinstatement. More importantly, clinical studies have also shown that OXT can exert beneficial effects on reducing substance use disorders of a series of drugs, such as heroin, cocaine, alcohol, cannabis and nicotine. Thus, the present review focuses on the role of OXT in treating drug addiction, including the preclinical and clinical therapeutic potential of OXT and its analogs on the neurobiological perspectives of drugs, to provide a better insight of the efficacy of OXT as a clinical addiction therapeutic agent.

Threshold for copulation-induced analgesia varies according to the ejaculatory endophenotypes in rats

Analgesia may be modulated by multiple internal and external factors. In prior studies, copulatory-induced analgesia was demonstrated using the vocalization threshold to tail shock (VTTS) in male and female rats. Three ejaculatory endophenotypes have been characterized in male Wistar rats based upon their ejaculation latency (EL). Since intromissions and ejaculations produce analgesia, and these copulatory patterns are performed with different frequency depending on the male's ejaculatory endophenotype, we hypothesized that copulation-induced analgesia would vary in relation to these endophenotypes. In the present study, we used three groups according to the EL (medians): rapid ejaculators (236 s; n = 21), intermediate ejaculators (663.2 s; n = 20) and sluggish ejaculators (1582.2 s; n = 8). Our aim was to evaluate whether copulation-induced analgesia is related to the ejaculatory endophenotypes during two consecutive ejaculatory series (EJS). In the first EJS, the VTTS of the rapid ejaculators was significantly higher than that of intermediate and sluggish rats. At the onset of the second EJS, the VTTS of the rapid and intermediate ejaculators was significantly higher than that of the sluggish rats. No differences in VTTS were observed during the first or second post-ejaculatory intervals among the three groups. These findings provide evidence that the more intromissions that occurred per unit time, the higher was the level of analgesia.

Are We missing out the role of oxytocin in overactive bladder syndrome?

Overactive bladder (OAB) is characterized by the storage symptoms of urgency with or without urgency incontinence. Although there is no clear cause of this idiopathic disease, overall prevalence of OAB symptoms in individuals aged 40 years old is more than 15%. Oxytocin, which is one of the most powerful contracting neuropeptide, was also shown to exhibit high intrinsic contractile activity on detrusor muscle. Oxytocin receptor antagonists that inhibit of bladder activity might offer new insights into the treatment of OAB.

The Oxytocin Antagonist Cligosiban Prolongs Intravaginal Ejaculatory Latency and Improves Patient-Reported Outcomes in Men with Lifelong Premature Ejaculation: Results of a Randomized, Double-Blind, Placebo-Controlled Proof-of-Concept Trial (PEPIX)

INTRODUCTION

Cligosiban is an orally administered oxytocin receptor antagonist being developed to treat premature ejaculation (PE).

AIM

To determine the safety and efficacy of cligosiban capsules (dose range 400-800 mg) to improve intravaginal ejaculation latency time (IELT) and patient-reported outcomes in men with severe lifelong PE.

METHODS

Patients recorded details of at least 4 sexual intercourse events during a 4-week run-in period, after which they underwent baseline assessments. Patients were eligible for the study if they rated their control of ejaculation as poor/very poor and their stopwatch-assessed IELT was ≤1 minute in ≥75% of intercourse attempts. Eligible patients were randomized to an 8-week treatment period with double-blind cligosiban or placebo (to be taken 1 to 6 hours prior to sexual activity). The starting dose was 400 mg (not more than 1 dose per day) which could be increased to 800 mg after 2 and/or 4 weeks of treatment. Assessments were conducted at 2, 4, and 8 weeks.

MAIN OUTCOME MEASURE

Efficacy measures were comprised of IELT, self-rating of ejaculation control and ejaculation-related distress (recorded in an electronic diary after each intercourse attempt), premature ejaculation profile, and the Clinical Global Impression of Change.

RESULTS

The mean ratio of fold change from baseline in IELT to the last 4 weeks of treatment (cligosiban/placebo) was 1.9 compared to a baseline of 1.0 (P = .0079). The mean increase in IELT from baseline to the last 4 weeks of treatment was 61.0 seconds for cligosiban, which was significantly different from (and 3.6-fold greater than) the mean increase of 16.4 seconds for placebo (P = .0086). Statistically significant improvements in ejaculation control and ejaculation-related personal distress scores were also observed for cligosiban compared to little or no change with placebo. Cligosiban was generally well tolerated, with no serious or severe adverse events or other safety parameters.

CLINICAL IMPLICATIONS

This proof-of-concept study demonstrated the potential for cligosiban, an oxytocin antagonist, to successfully treat symptoms of severe lifelong PE.

STRENGTHS AND LIMITATIONS

This was a Phase II, randomized, double-blind, placebo-controlled study that was adequately powered to detect a clinically meaningful difference in change in IELT between cligosiban and placebo. Larger studies will be needed to confirm these findings, determine the optimal dose of cligosiban and assess efficacy in men with acquired PE.

CONCLUSIONS

Cligosiban was well tolerated, and resulted in significant benefits in both objective and subjective measures of ejaculatory control in men with lifelong PE and therefore offers significant potential as an on-demand, orally administered agent for the treatment of PE. McMahon C, Althof S, Rosen R, et al. The Oxytocin Antagonist Cligosiban Prolongs Intravaginal Ejaculatory Latency and Improves Patient-Reported Outcomes in Men with Lifelong Premature Ejaculation: Results of a Randomized, Double-Blind, Placebo-Controlled Proof-of-Concept Trial (PEPIX). J Sex Med 2019; 16:1178-1187.

Empathy as a Concept from Bench to Bedside: A Translational Challenge

Empathy is a multidimensional paradigm, and there currently is a lack of scientific consensus in its definition. In this paper, we review the possibility of compromising data during behavioral neuroscience experiments, including but not limited to those who study empathy. The experimental protocols can affect, and be affected by, empathy and related processes at multiple levels. We discuss several points to help researchers develop a successful translational pathway for behavioral research on empathy. Despite varying in their focus with no widely accepted model, current rodent models on empathy have provided sound translational explanations for many neuropsychiatric proof-of-concepts to date. Research has shown that empathy can be influenced by many parameters, some of which are to be reviewed in this paper. We emphasize the future importance of consistency in modeling proof of concept; efforts to create a multidisciplinary group which would include both bench scientists and clinicians with expertise in neuropsychiatry, and the consideration of empathy as an independent variable in animal behavioral experimental designs which is not the mainstream practice at present.

Berberine hydrochloride attenuates voluntary methamphetamine consumption and anxiety-like behaviors via modulation of oxytocin receptors in methamphetamine addicted rats

OBJECTIVE

Methamphetamine (METH) addiction is recognized as one of the major public health concerns, with no approved pharmacological agents for treatment. Berberine hydrochloride, an isoquinoline alkaloid in plants, induces antipsychotic and anxiolytic effects. Hence, we hypothesized that berberine may modulate the METH-induced rewarding effects.

MATERIALS AND METHODS

In this study, three groups of rat including control (N = 10), METH + vehicle (N = 10), and METH + berberine (N = 10) were kept in separate cages one day before expriments. METH (20 mg/L) was dissolved in tap water inside a bottle, while there was only tap water in the control bottle. Two groups received free METH solutions for two weeks (up to 12 mg/kg). Afterwards, they were abstianced for three weeks. Only one group received 100 mg/kg/day of berberine. After three weeks, locomotor activity and anxiety (elevated plus maze test) were evaluated, then the two-bottles choice model was used for one week to evaluate drug preferences. Finally, the brain of rats was removed for evaluation of oxytocin receptor expression via immunofluorescence staining method.

RESULTS

The results showed that METH preference was lower in the berberine + METH group during drug intake compared to the METH group (P < .05). During withdrawal, berberine reduced anxiety-like behaviors (P < .05) and decreased locomotor activity versus the METH group (P < .001). Also, berberine increased numbers of oxytocin receptors in comparison with the METH group (P < .01).

CONCLUSION

Considering the modulation of oxytocin receptors, berberine may be considered as a potential therapeutic agent for METH addiction.

Rats selectively bred for showing divergent behavioral traits in response to stress or novelty or spontaneous yawning with a divergent frequency show similar changes in sexual behavior: the role of dopamine

Sexual behavior plays a fundamental role for reproduction in mammals and other animal species. It is characterized by an anticipatory and a consummatory phase, and several copulatory parameters have been identified in each phase, mainly in rats. Sexual behavior varies significantly across rats even when they are of the same strain and reared under identical conditions. This review shows that rats of the same strain selectively bred for showing a divergent behavioral trait when exposed to stress or novelty (i.e. Roman high and low avoidance rats, bred for their different avoidance response to the shuttle box, and high and low novelty exploration responders rats, bred for their different exploratory response to a novel environment) or a spontaneous behavior with divergent frequency (i.e. low and high yawning frequency rats, bred for their divergent yawning frequency) show similar differences in sexual behavior, mainly in copulatory pattern, but also in sexual motivation. As shown by behavioral pharmacology and intracerebral microdialysis experiments carried out mainly in Roman rats, these sexual differences may be due to a more robust dopaminergic tone present in the mesocorticolimbic dopaminergic system of one of the two sub-lines (e.g. high avoidance, high novelty exploration, and low yawning rat sub-lines). Thus, differences in genotype and/or in prenatal/postnatal environment lead not only to individual differences in temperament and environmental/emotional reactivity but also in sexual behavior. Because of the highly conserved mechanisms controlling reproduction in mammals, this may occur not only in rats but also in humans.

The Oxytocin Receptor: From Intracellular Signaling to Behavior

The many facets of the oxytocin (OXT) system of the brain and periphery elicited nearly 25,000 publications since 1930 (see FIGURE 1 , as listed in PubMed), which revealed central roles for OXT and its receptor (OXTR) in reproduction, and social and emotional behaviors in animal and human studies focusing on mental and physical health and disease. In this review, we discuss the mechanisms of OXT expression and release, expression and binding of the OXTR in brain and periphery, OXTR-coupled signaling cascades, and their involvement in behavioral outcomes to assemble a comprehensive picture of the central and peripheral OXT system. Traditionally known for its role in milk let-down and uterine contraction during labor, OXT also has implications in physiological, and also behavioral, aspects of reproduction, such as sexual and maternal behaviors and pair bonding, but also anxiety, trust, sociability, food intake, or even drug abuse. The many facets of OXT are, on a molecular basis, brought about by a single receptor. The OXTR, a 7-transmembrane G protein-coupled receptor capable of binding to either Gαior Gαqproteins, activates a set of signaling cascades, such as the MAPK, PKC, PLC, or CaMK pathways, which converge on transcription factors like CREB or MEF-2. The cellular response to OXT includes regulation of neurite outgrowth, cellular viability, and increased survival. OXTergic projections in the brain represent anxiety and stress-regulating circuits connecting the paraventricular nucleus of the hypothalamus, amygdala, bed nucleus of the stria terminalis, or the medial prefrontal cortex. Which OXT-induced patterns finally alter the behavior of an animal or a human being is still poorly understood, and studying those OXTR-coupled signaling cascades is one initial step toward a better understanding of the molecular background of those behavioral effects.

Role of central oxytocin and dopamine systems in nociception and their possible interactions: suggested hypotheses

Central oxytocin and dopamine have an important role in the process of nociception at the spinal level as well as supraspinal structures, e.g. anterior cingulate cortex, insular cortex, amygdala, nucleus accumbens, and hypothalamus. Many studies have pointed out the importance of both systems in the pain descending modulatory system and in pain-related symptoms in some chronic disorders, e.g. Parkinson disease and fibromyalgia. The interaction between oxytocin and dopamine systems has been addressed in some motivational behaviors, e.g. maternal and sexual behaviors, pair bonding, and salience. In this aspect, we propose that an oxytocin-dopamine interaction could be present in nociception, and we also explain the possible hypotheses of such an interaction between these systems.

A Review of the Safety, Efficacy and Mechanisms of Delivery of Nasal Oxytocin in Children: Therapeutic Potential for Autism and Prader-Willi Syndrome, and Recommendations for Future Research

In this article, we conduct a comprehensive review of existing evidence for the safety and therapeutic potential of intranasal oxytocin in pediatric populations. Unique considerations for dosing and delivery of oxytocin to the nasal passageway in pediatric populations and methods to promote adherence are reviewed. Intranasal oxytocin has been administered to 261 children in three open-label studies and eight randomized controlled trials. To date, the only published results in pediatric populations have focused on autism spectrum disorder (ASD) and Prader-Willi syndrome (PWS). Results regarding efficacy for improving social impairment in ASD are equivocal, partially due to mixed methodological designs, dosing regimens, and outcome measures. At present, there is no randomized controlled evidence that oxytocin provides benefit to individuals with PWS. There is no clear evidence of a link between oxytocin administration and any specific adverse event. Adverse events have been assessed using medical interviews, open reports, checklists, and physiological assessments. Adverse events reports have been largely classified as mild (n = 93), with few moderate (n = 9) or severe (n = 3) events reported. There were 35 additional adverse events reported, without severity ratings. Severe events, hyperactivity and irritability, occurred at first administration in both placebo and oxytocin groups, and subsided subsequent to discontinuation. We note that adverse event monitoring is inconsistent and often lacking, and reporting of its relationship to the study drug is poor. Only one study reported adherence data to suggest high adherence. Recommendations are then provided for the delivery of nasal sprays to the nasal passageway, monitoring, and reporting of efficacy, safety, and adherence for oxytocin nasal spray trials in pediatric populations.

Oxytocin in the socioemotional brain: implications for psychiatric disorders

The neuropeptide oxytocin (OXT), highly conserved during evolution, is an important modulator of social and emotional processes across many species. During the last decade, a large body of literature has revealed its effects on different aspects of social behavior, including social stress and anxiety, social memory, affiliation and bonding, emotion recognition, mentalizing, empathy, and interpersonal trust. In addition, as impairments in these social domains can be observed in a number of neuropsychiatric disorders, such as autism, social anxiety disorder, depression, schizophrenia, and borderline personality disorder, the role of OXT in mental disorders and their treatment has been intensively studied. The present paper gives a short overview of these lines of research and shows how OXT has become a promising target for novel treatment approaches for mental disorders characterized by social impairments.

The neurocircuitry involved in oxytocin modulation of methamphetamine addiction

The role of oxytocin in attenuating the abuse of licit and illicit drugs, including the psychostimulant methamphetamine, has been examined with increased ferocity in recent years. This is largely driven by the potential application of oxytocin as a pharmacotherapy. However, the neural mechanisms by which oxytocin modulates methamphetamine abuse are not well understood. Recent research identified an important role for the accumbens core and subthalamic nucleus in this process, which likely involves an interaction with dopamine, glutamate, GABA, and vasopressin. In addition to providing an overview of methamphetamine, the endogenous oxytocin system, and the effects of exogenous oxytocin on drug abuse, we propose a neural circuit through which exogenous oxytocin modulates methamphetamine abuse, focusing on its interaction with neurochemicals within the accumbens core and subthalamic nucleus. A growing understanding of exogenous oxytocin effects at a neurochemical and neurobiological level will assist in its evaluation as a pharmacotherapy for drug addiction.

Emerging and investigational drugs for premature ejaculation

Over the past 20−30 years, the premature ejaculation (PE) treatment paradigm, previously limited to behavioural psychotherapy, has expanded to include drug treatment. Pharmacotherapy for PE predominantly targets the multiple neurotransmitters and receptors involved in the control of ejaculation which include serotonin, dopamine, oxytocin, norepinephrine, gamma amino-butyric acid (GABA) and nitric oxide (NO). The objective of this article is to review emerging PE interventions contemporary data on the treatment of PE was reviewed and critiqued using the principles of evidence-based medicine. Multiple well-controlled evidence-based studies have demonstrated the efficacy and safety of selective serotonin reuptake inhibitors (SSRIs) in delaying ejaculation, confirming their role as first-line agents for the medical treatment of lifelong and acquired PE. Daily dosing of SSRIs is likely to be associated with superior fold increases in IELT compared to on-demand SSRIs. On-demand SSRIs are less effective but may fulfill the treatment goals of many patients. Integrated pharmacotherapy and CBT may achieve superior treatment outcomes in some patients. PDE-5 inhibitors alone or in combination with SSRIs should be limited to men with acquired PE secondary to co-morbid ED. New on-demand rapid acting SSRIs, oxytocin receptor antagonists, or single agents that target multiple receptors may form the foundation of more effective future on-demand medication. Current evidence confirms the efficacy and safety of dapoxetine, off-label SSRI drugs, tramadol and topical anaesthetics drugs. Treatment with α1-adrenoceptor antagonists cannot be recommended until the results of large well-designed RCTs are published in major international peer-reviewed medical journals. As our understanding of the neurochemical control of ejaculation improves, new therapeutic targets and candidate molecules will be identified which may increase our pharmacotherapeutic armamentarium.

Early adverse experience and substance addiction: dopamine, oxytocin, and glucocorticoid pathways

Substance addiction may follow a chronic, relapsing course and critically undermine the physical and psychological well-being of the affected individual and the social units of which the individual is a member. Despite the public health burden associated with substance addiction, treatment options remain suboptimal, with relapses often seen. The present review synthesizes growing insights from animal and human research to shed light upon developmental and neurobiological pathways that may increase susceptibility to addiction. We examine the dopamine system, the oxytocin system, and the glucocorticoid system, as they are particularly relevant to substance addiction. Our aim is to delineate how early adverse experience may induce long-lasting alterations in each of these systems at molecular, neuroendocrine, and behavioral levels and ultimately lead to heightened vulnerability to substance addiction. We further discuss how substance addiction in adulthood may increase the risk of suboptimal caregiving for the next generation, perpetuating the intergenerational cycle of early adverse experiences and addiction.

Potential of Oxytocin in the Treatment of Schizophrenia

Schizophrenia is a heterogeneous, debilitating disorder characterized by three distinct sets of clinical features: positive symptoms, negative symptoms, and cognitive deficits. Extant antipsychotic drugs have been most successful at treating the positive symptoms of patients with schizophrenia but have minimal therapeutic effects on negative symptoms and cognitive deficits, which are the symptoms that best predict the poor prognosis of these patients. Therefore, there has been a major effort towards identifying compounds that alleviate these symptoms. Oxytocin (OT) is a nonapeptide that regulates peripheral reproductive-relevant functions, and also acts as a neurotransmitter in the brain. Converging evidence from both preclinical and clinical research suggests that OT may have therapeutic efficacy for the positive symptoms, negative symptoms, and cognitive deficits of schizophrenia. In the majority of the small, randomized, placebo-controlled clinical trials conducted to date, OT has shown particular promise in its potential to treat the intractable negative symptoms and social cognitive deficits exhibited by most of the patients with this debilitating disorder. In this leading article, we summarize the clinical evidence relevant to (1) endogenous OT and schizophrenia, and (2) the putative therapeutic effects of OT on each of the three clinical domains.

Salsolinol Up-Regulates Oxytocin Expression and Release During Lactation in Sheep

Salsolinol (1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline) is a dopamine-derived compound present in the central nervous system and pituitary gland. Several previous studies on lactating sheep and rats have reported that salsolinol plays a crucial role in the regulation of prolactin secretion. The present study investigated the effects of salsolinol, which was infused into the third ventricle of the brain, on oxytocin expression and release in lactating sheep, 48 h after weaning of 8-week-old lambs. Serial 30-min infusions of salsolinol and vehicle were performed at 30-min intervals from 10.00 to 15.00 h. Blood samples were collected every 10 min. The supraoptic nucleus (SON), paraventricular nucleus (PVN) and posterior pituitary were collected immediately after the experiment. Expression levels of mRNAs for oxytocin and peptidylglycine α-amidating monooxygenase (PAM), the terminal enzyme in the oxytocin synthesis pathway, were measured using a real-time polymerase chain reaction. Oxytocin peptide content in the posterior pituitary was measured by an enzyme-linked immunosorbent assay, and plasma oxytocin concentration was measured by radioimmunoassay. Salsolinol treatment significantly up-regulated oxytocin and PAM gene expression in the SON (P < 0.01 and P < 0.05, respectively), PVN (P < 0.01 and P < 0.05, respectively) and posterior pituitary (P < 0.05 and P < 0.05, respectively). Oxytocin peptide content in the posterior pituitary and the area under the response curve of plasma oxytocin were significantly (P < 0.05 and P < 0.01, respectively) higher in salsolinol-treated sheep than in control animals. The present study shows for the first time that salsolinol stimulates oxytocin secretion during lactation in sheep.

Oxytocin in the nucleus accumbens core reduces reinstatement of methamphetamine-seeking behaviour in rats

The psychostimulant methamphetamine (METH) is an addictive illicit drug. Systemic administration of the neuropeptide oxytocin modulates METH-related reward and METH-seeking behaviour. Recent findings demonstrated a reduction in METH-induced reward by oxytocin administration into the nucleus accumbens (NAc) core. It is not known, however, if oxytocin acts in this region to reduce relapse to METH-seeking behaviour. Using the drug reinstatement paradigm in rats experienced at METH self-administration, we aimed to determine whether oxytocin pre-treatment within the NAc core would reduce relapse to METH use and if this could be reversed by the co-administration of the oxytocin receptor (OTR) antagonist desGly-NH2,d(CH2)5[D-Tyr2,Thr4]OVT. Male Sprague-Dawley rats underwent surgery to implant an intravenous jugular vein catheter and bilateral microinjection cannulae in the NAc core. Rats were then trained to self-administer intravenous METH (0.1 mg/kg/infusion) by lever press during 2-hour fixed ratio 1 scheduled sessions for 20 days. Following extinction of lever press activity, the effect of microinjecting saline, oxytocin (0.5 pmol, 1.5 pmol, 4.5 pmol) or co-administration of oxytocin (1.5 pmol) and desGly-NH2,d(CH2)5[D-Tyr2,Thr4]OVT (1 nmol, 3 nmol) in the NAc core (500 nl/side) was examined on METH-primed (1 mg/kg, i.p.) reinstatement of drug-seeking behaviour. Our results showed oxytocin directly administered into the NAc core decreased METH-primed reinstatement in a dose-dependent manner. Co-administration of the selective OTR antagonist did not specifically reverse the inhibitory effects of oxytocin on METH priming, suggesting mediation by receptors other than the OTR. These findings highlight an important modulatory effect of oxytocin in the NAc core on relapse to METH seeking.

Affect development as a need to preserve homeostasis

In this review, we aim to present our hypothesis about the neural development of affect. According to this view, affect develops at a multi-layered process, and as a mediator between drives, emotion and cognition. This development is parallel to the evolution of the brain from reptiles to mammals. There are five steps in this process: (1) Because of the various environmental challenges, changes in the autonomic nervous system occur and homeostasis becomes destabilized; (2) Drives arise from the destabilized homeostasis; (3) Drives trigger the neural basis of the basic emotional systems; (4) These basic emotions evolve into affect to find the particular object to invest the emotional energy; and (5) In the final stage, cognition is added to increase the possibility of identifying a particular object. In this paper, we will summarize the rationale behind this view, which is based on neuroscientific proofs, such as evolution of autonomic nervous system, neural basis the raw affective states, the interaction between affect and cognition, related brain areas, related neurotransmitters, as well as some clinical examples.

From Autism to Eating Disorders and More: The Role of Oxytocin in Neuropsychiatric Disorders

Oxytocin (oxy) is a pituitary neuropeptide hormone synthesized from the paraventricular and supraoptic nuclei within the hypothalamus. Like other neuropeptides, oxy can modulate a wide range of neurotransmitter and neuromodulator activities. Additionally, through the neurohypophysis, oxy is secreted into the systemic circulation to act as a hormone, thereby influencing several body functions. Oxy plays a pivotal role in parturition, milk let-down and maternal behavior and has been demonstrated to be important in the formation of pair bonding between mother and infants as well as in mating pairs. Furthermore, oxy has been proven to play a key role in the regulation of several behaviors associated with neuropsychiatric disorders, including social interactions, social memory response to social stimuli, decision-making in the context of social interactions, feeding behavior, emotional reactivity, etc. An increasing body of evidence suggests that deregulations of the oxytocinergic system might be involved in the pathophysiology of certain neuropsychiatric disorders such as autism, eating disorders, schizophrenia, mood, and anxiety disorders. The potential use of oxy in these mental health disorders is attracting growing interest since numerous beneficial properties are ascribed to this neuropeptide. The present manuscript will review the existing findings on the role played by oxy in a variety of distinct physiological and behavioral functions (Figure 1) and on its role and impact in different psychiatric disorders. The aim of this review is to highlight the need of further investigations on this target that might contribute to the development of novel more efficacious therapies. Figure 1

Effect of dopamine D4 receptor agonists on sleep architecture in rats

Dopamine plays a key role in the regulation of sleep-wake states, as revealed by the observation that dopamine-releasing agents such as methylphenidate have wake-promoting effects. However, the precise mechanisms for the wake-promoting effect produced by the enhancement of dopamine transmission are not fully understood. Although dopamine D1, D2, and D3 receptors are known to have differential effects on sleep architecture, the role of D4 receptors (D4Rs), and particularly the influence of D4R activation on the sleep-wake state, has not been studied so far. In this study, we investigated for the first time the effects of two structurally different D4R agonists, Ro 10-5824 and A-412997, on the sleep-wake states in rats. We found that both D4R agonists generally increased waking duration, and conversely, reduced non-rapid eye movement (NREM) sleep duration in rats. The onset of NREM sleep was also generally delayed. However, only the A-412997 agonist (but not the Ro 10-5824) influenced rapid eye movement sleep onset and duration. Furthermore, these effects were accompanied with an enhancement of EEG spectral power in the theta and the gamma bands. Our results suggest the involvement of dopamine D4R in the regulation of sleep-wake states. The activation of the D4R could enhance the arousal states as revealed by the behavioral and electrophysiological patterns in this study. Dopamine D4R may contribute to the arousal effects of dopamine-releasing agents such as methylphenidate.

Current and Emerging Treatments for Premature Ejaculation

INTRODUCTION

Over the past 20-30 years, the premature ejaculation (PE) treatment paradigm, previously limited to behavioral psychotherapy, has expanded to include drug treatment. Pharmacotherapy for PE predominantly targets the multiple neurotransmitters and receptors involved in the control of ejaculation, which include serotonin, dopamine, oxytocin, norepinephrine, gamma amino-butyric acid (GABA) and nitric oxide (NO).

AIM

The objective of this article is to review current and emerging PE interventions.

METHODS

Contemporary data on the treatment of PE were reviewed and critiqued using the principles of evidence-based medicine.

MAIN OUTCOME MEASURE

Integrated pharmacotherapy and cognitive behavioral therapy (CBT) may achieve superior treatment outcomes in some patients. Phosphodiesterase type 5 inhibitors alone or in combination with selective serotonin reuptake inhibitors (SSRIs) should be limited to men with acquired PE secondary to comorbid erectile dysfunction (ED). New on-demand rapid-acting SSRIs, oxytocin receptor antagonists, or single agents that target multiple receptors may form the foundation of more effective future on-demand medication.

RESULTS

Multiple well-controlled evidence-based studies have demonstrated the efficacy and safety of SSRIs in delaying ejaculation, confirming their role as first-line agents for the medical treatment of lifelong and acquired PE. Daily dosing of SSRIs is likely to be associated with superior fold increases in intravaginal ejaculation latency time compared with on-demand SSRIs. On-demand SSRIs are less effective but may fulfill the treatment goals of many patients.

CONCLUSIONS

Current evidence suggests that psychosexual CBT has a limited role in the contemporary management of PE and confirms the efficacy and safety of dapoxetine, off-label SSRI drugs, and topical anesthetics drugs. Treatment with tramadol, α1-adrenoceptor antagonists cannot be recommended until the results of large, well-designed randomized controlled trials are published in major international peer-reviewed medical journals. As our understanding of the neurochemical control of ejaculation improves, new therapeutic targets and candidate molecules will be identified, which may increase our pharmacotherepeutic armamentarium. McMahon CG. Current and emerging treatments for premature ejaculation. Sex Med Rev 2015;3:183-202.

Oxytocin and vasopressin: linking pituitary neuropeptides and their receptors to social neurocircuits

Oxytocin and vasopressin are pituitary neuropeptides that have been shown to affect social processes in mammals. There is growing interest in these molecules and their receptors as potential precipitants of, and/or treatments for, social deficits in neurodevelopmental disorders, including autism spectrum disorder. Numerous behavioral-genetic studies suggest that there is an association between these peptides and individual social abilities; however, an explanatory model that links hormonal activity at the receptor level to complex human behavior remains elusive. The following review summarizes the known associations between the oxytocin and vasopressin neuropeptide systems and social neurocircuits in the brain. Following a micro- to macro- level trajectory, current literature on the synthesis and secretion of these peptides, and the structure, function and distribution of their respective receptors is first surveyed. Next, current models regarding the mechanism of action of these peptides on microcircuitry and other neurotransmitter systems are discussed. Functional neuroimaging evidence on the acute effects of exogenous administration of these peptides on brain activity is then reviewed. Overall, a model in which the local neuromodulatory effects of pituitary neuropeptides on brainstem and basal forebrain regions strengthen signaling within social neurocircuits proves appealing. However, these findings are derived from animal models; more research is needed to clarify the relevance of these mechanisms to human behavior and treatment of social deficits in neuropsychiatric disorders.