Differences in sympathetic nervous system activity and NMDA receptor levels within the hypothalamic paraventricular nucleus in rats with differential ejaculatory behavior

Altered brain activity associated with premature ejaculation improved by electroacupuncture in rats

Background

Premature ejaculation (PE) is linked with abnormal brain activity that is modifiable by electroacupuncture (EA).

Aim

In this study we aimed to explore the central pathological mechanism underlying EA in treating PE.

Methods

Six-week-old male Sprague-Dawley rats were divided into a PE group (n = 8) and a control group (n = 8) according to ejaculatory frequency during copulatory behavior. All rats underwent EA at the Zusanli acupoint (ST-36) for 4 weeks. Magnetic resonance imaging data were collected before and after EA.

Outcomes

The behavioral parameters, plasma norepinephrine levels, fractional amplitude of low frequency fluctuation (fALFF), and regional homogeneity (ReHo) were evaluated.

Results

The PE group ejaculated more times with shorter latency compared with controls. After EA, the ejaculation frequency of the PE group decreased, and the ejaculation latency period increased, with no changes observed in the control group. Norepinephrine levels were higher in the PE group than in the controls and were positively correlated with ejaculation frequency and negatively correlated with ejaculation latency. The PE group showed lower fALFF in the right striatum and higher ReHo in the brainstem compared with controls. After EA, controls showed decreased fALFF in the right striatum, left olfactory bulb, and dorsal fornix and increased ReHo in the right interpeduncular nucleus, as well as decreased ReHo in the left striatum, prelimbic system, right basal forebrain region, septal region, and olfactory bulb, while the model group exhibited increased fALFF in the right hypothalamic region, decreased fALFF in the left globus pallidum and right basal forebrain region and increased ReHo in the right interpeduncular nucleus, as well as decreased ReHo in the left striatum, olfactory bulb, basal forebrain region, dentate gyrus, right dysgranular insular cortex, and striatum. Compared with the controls after EA, the model group showed increased ReHo of the right hypothalamic region and decreased ReHo of the right dysgranular insular cortex.

Clinical Implications

These findings might enhance the understanding of PE and contribute to new, targeted therapies for PE.

Strengths and Limitations

The therapeutic effects might be achieved by EA inhibiting the activity in brain regions involved in ejaculatory behavior. However, the curative effect of acupuncture might be underestimated due to some curative effects of sham acupuncture used in the control group.

Conclusion

In conclusion, the ejaculatory frequency of rats may be reduced and ejaculation latency could be extended by EA at ST-36, which might be achieved by the effects of this treatment on brain activity.

Rapid ejaculator rats are more susceptible to anxiety compared with normal ejaculator rats

By observation of Sprague-Dawley male rats with different ejaculatory behaviors, we have identified distinct behavioral characteristics in rapid ejaculator rats. To validate these differential behaviors, we conducted multifaceted behavioral experiments on rapid ejaculator rats and normal rats. Through mating experiments, 42 male rats were categorized into 5 rapid ejaculator rats, 29 normal ejaculator rats, and 8 sluggish ejaculator rats according to their ejaculation frequency. We selected 5 rats exhibiting rapid ejaculation and 5 rats with normal ejaculation for participation in the Morris water maze, open-field test, and balance beam experiments. The open-field tests revealed that rapid ejaculator rats spent shorter time in the center region (1.23 ± 1.21 vs. 6.56 ± 2.40 s, P = 0.0041), less entered the center region (0.80 ± 0.75 vs. 3.40 ± 1.50, time, P = 0.0145), traveled shorter distances (17,003.77 ± 3339.42 vs. 25,037.90 ± 5499.94 mm, P = 0.0371), and had a lower average speed compared with normal rats (66.09 ± 62.36 vs. 195.56 ± 83.41 mm/s, P = 0.0377). However, no significant differences were observed in the Morris water maze and balance beam experiments (0.25 ± 0.05 vs. 0.26 ± 0.07, P = 0.7506;16.40 ± 3.77 vs. 16.25 ± 2.05, P = 0.9515). These behavioral results indicated that the rapid ejaculator rats were more prone to anxiety. To further substantiate this claim, we examined Brain-derived neurotrophic factor expression levels in the hippocampus of rat brains using immunohistochemistry and western blotting. The results demonstrate lower Brain-derived neurotrophic factor expression in the hippocampus of rapid ejaculator rats compared with that in normal rats (P = 0.0093). Thus, our experiments indicate that rapid ejaculator rats exhibit a higher propensity for anxiety, potentially linked to their abnormal neurophysiologic state. It is concluded that rapid ejaculator rats may be more susceptible to anxiety on a pathophysiological basis.

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.

Multidisciplinary approach and management of patients who seek medical advice for penile size concerns: a narrative review

We aimed to provide an overview of the strategies available to manage patients concerned about their penile size and to provide useful surgical hints regarding the most common penile enlargement approaches, based on our surgical expertise in this field. A comprehensive research was carried out on MEDLINE/PubMed database to identify pertinent studies concerning penile enlargement issues. The search strategy included a range of keywords; e.g. penis, penile, enlargement, augmentation, lengthening, girth. Management of penile size-related concerns represents a real challenge for the urologist, especially when dealing with patients suffering from penile dysmorphophobic disorder (PDD). A multidisciplinary preoperative assessment, including a psychiatric/psychological evaluation, may help in discerning those patients who would benefit the most from counselling/conservative management from those who would benefit from surgery instead. Conservative approaches include the use of vacuum-based and penile-stretching devices, which have shown encouraging levels of efficacy and safety. Over the last decades, different surgical strategies have been developed, aimed at either increasing flaccid penile length or improving penile girth. Penile lengthening procedures are more established, and satisfactory results can be achieved by experienced, large referrals' volume, surgeons. To date, there is lack of consensus regarding the penile girth enhancing techniques, and therefore these should be regarded as experimental. A multidisciplinary approach is necessary to identify patients with PDD, who should not be offered surgical intervention and should be referred for psychiatric/psychological counselling instead. The surgical approach should be tailored to the subject's unique anatomy and underlying conditions.

D-aspartic Acid Supplementation Effects on Body Composition: A Systematic Review of Randomized Clinical Trials on Trained Males

Context: D-Aspartic acid (DAA) is an amino acid found in the brain and reproductive system. Some investigations have reported beneficial effects of DAA on brain function and reproductive system health by increasing testosterone through the hypothalamic-pituitary-gonadal axis. However, its effect on body composition is unknown. Given testosterone's role in muscle growth, this study aimed to evaluate the effect of DAA supplementation on the body composition of trained males. Evidence Acquisition: PubMed, Scopus, Embase, and Web of Science (until 1 August 2021) were searched for this systematic review. Inclusion criteria assumed as clinical trials assessed the effect of DAA on body composition in trained males. After including articles by keywords, the articles were reviewed for meeting the eligibility criteria. Three independent researchers conducted the search and full-text review. Results: Among 134 articles located during the primary search, five articles (47 interventions and 43 controls) were included in the study based on eligibility criteria. All included clinical trials had a low risk of bias. A review of the relevant literature concludes that different doses of DAA (three grams, six grams, 7.12, and 12 grams) in different intervention periods (two weeks, four weeks, and 12 weeks) have no effects on body composition in trained males. Conclusions: DAA supplementation is a low-level booster of testosterone and has no significant effect on the testosterone level in professional male athletes, and cannot alter the body composition.

The upregulation of tryptophan hydroxylase-2 expression is important for premature ejaculation treatment with the selective serotonin reuptake inhibitor

BACKGROUND

Although there was some evidence to suggest that the serotonergic system in the brain played an important role in premature ejaculation (PE), tryptophan hydroxylase-2 (TPH2) is considered to be the key enzyme for the synthesis of 5-hydroxytryptamine (5-HT) and few studies have reported that brain TPH2 is involved in the regulation of ejaculation.

OBJECTIVES

This study aimed to investigate whether changes in brain TPH2 levels were associated with PE and to explore the effects of acute administration of dapoxetine on TPH2 expression in the brain of rats with rapid ejaculation.

MATERIALS AND METHODS

Based on the ejaculation frequency, the male rats were split into three groups: "rapid," "normal," and "sluggish" ejaculators. The level of 5-HT in the brain was determined by an enzyme-linked immunosorbent assay. TPH2 expression was detected by western blot analysis and immunohistochemistry.

RESULTS

The results showed that the concentration of 5-HT and the expression of TPH2 in rapid rats were the lowest, while those in sluggish rats were the highest. Correlation analysis also indicated the level of TPH2 was positively correlated with ejaculation latency (r = 0.8633, p < 0.0001) and negatively correlated with ejaculation frequency (r = -0.874, p < 0.001). In addition, dapoxetine acute administration to rapid rats resulted in upregulation of TPH2 expression in the brain.

DISCUSSION

There was an important link between the level of TPH2 and the change of ejaculation behaviors. Decreased expression of TPH2 in relevant brain regions will lead to rapid ejaculation. Moreover, the effect of dapoxetine on prolonging ejaculation may be due to the upregulation of TPH2 expression.

CONCLUSION

We found the correlation between the level of TPH2 in the brain and PE. The findings in this study will open up a novel way for future research in PE therapy.

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.

Abnormal Functional Connectivity Between the Left Medial Superior Frontal Gyrus and Amygdala Underlying Abnormal Emotion and Premature Ejaculation: A Resting State fMRI Study

Introduction

Premature ejaculation (PE) is a common sexual dysfunction and is found to be associated with abnormal emotion. The amygdala plays an important role in the processing of emotion. The process of ejaculation is found to be mediated by the frontal-limbic neural circuits. However, the correlations between PE and emotion are still unclear.

Methods

Resting-state functional magnetic resonance imaging (rs-fMRI) data were acquired in 27 PE patients with stable emotion (SPE), 27 PE patients with abnormal emotion (NPE), and 30 healthy controls (HC). We used rs-fMRI to explore the underlying neural mechanisms in SPE, NPE, and HC by measuring the functional connectivity (FC). Differences of FC values among the three groups were compared when choosing bilateral amygdala as the regions of interest (ROIs). We also explored the correlations between the brain regions showing altered FC values and scores of the premature ejaculation diagnostic tool (PEDT)/Eysenck Personality Inventory about neuroticism (EPQ-N) in the PE group.

Results

When the left amygdala was chosen as the ROI, the SPE group exhibited an increased FC between the left medial superior frontal gyrus (SFGmed) and amygdala compared with the NPE or HC group. When the right amygdala was chosen as the ROI, the NPE group exhibited a decreased FC between the left SFGmed and right amygdala compared with the HC group. In addition, FC values of the left SFGmed had positive correlations with PEDT and negative correlations with EPQ-N scores in the PE group. Moreover, FC values of the left superior temporal gyrus had positive correlations with EPQ-N scores in the PE group.

Conclusion

The increased FC values between the left SFGmed and amygdala could reflect a compensatory cortical control mechanism with the effect of stabilized emotion in the limbic regions of PE patients. Abnormal FC between these brain regions could play a critical role in the physiopathology of PE and could help us in dividing PE into more subtypes.

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.

Blunt olfaction in sexually sluggish male rats

Among the intact male rats, a subpopulation has been found to show little or no sexual behavior, even after experiencing several mating sessions. This study investigated whether sexually sluggish (SS) males show behavioral differences from normal copulatory (NC) males, other than those concerning sexual behavior. The olfactory preference of males was measured through the time spent displaying nose-poking behavior directed at sexually active males and estrous females for odor exploration in a three-chamber apparatus. Both the NC and SS males showed a significant preference for the odor of estrous females compared with that of male odors. However, SS males spent significantly less time nose-poking estrous females than NC males. The food-finding test was performed after overnight fasting. Our findings showed that all the NC males found the buried pellet within 5 min, whereas over 60% of the SS males failed to find it. The males were also tested for their ability to find a buried bag containing soiled bedding from estrous female cages. The bag was found by 80% of NC males, but only by 20% of SS males. Our results suggest that SS and NC male rats differ not only in sexual behavior but also in other functions such as olfaction.

Complications of glans penis augmentation

Despite the controversy regarding penile augmentation (PA), glans penis augmentation (GPA) is used in penile reconstructive surgery in selected patients with small glans penis. Since 2003, injectable hyaluronic acid (HA) gel has been used for GPA. The attractiveness of HA gel fillers and interest in this technique have led to the use of other fillers for GPA, particularly irreversible fillers that improve the longevity of HA gels. Conversely, indirect glans augmentation via implantation of dermofat grafts or scaffolds between the corpus spongiosum and the distal tip of the corpus cavernosum is used to overcome poor longevity of the gel and glans surface undulation, which are the primary limitations of GPA using HA gel. Unfortunately, these implants form hard painful lumps over time in most patients and are difficult to remove. Blunt dissection is an invasive procedure that may cause vascular compromise and consequent glans necrosis in a few patients. We present our review regarding the current status of GPA for a more comprehensive understanding of this subject. Additionally, we have discussed a few complicated cases that were referred to us.