Inhibitory Role of Gamma-Aminobutyric Receptors in Paraventricular Nucleus on Ejaculatory Responses in Rats

The association between shift work, shift work sleep disorders and premature ejaculation in male workers

OBJECTIVE

Shift work and Shift Work Sleep Disorder (SWSD) are known to affect the secretion of several neurotransmitters and hormones associated with premature ejaculation (PE). However, their specific influence on the regulation of male ejaculation remains unclear. This study explores the relationship between shift work, SWSD, and PE.

METHODS

From April to October 2023, a cross-sectional survey was conducted across five regions of China to explore the work schedules, sleep quality, and sexual function of male workers. Participants' sleep quality was evaluated using a validated SWSD questionnaire, and their erectile function and ejaculatory control were assessed with the International Inventory of Erectile Function (IIEF-5) scores and Premature Ejaculation Diagnostic Tool (PEDT) scores, respectively. Univariate and multivariate linear regression analyses were employed to identify risk factors associated with PE. Confounders were controlled using multiple regression models, and clinical prediction models were developed to predict PE onset and assess the contribution of risk factors.

RESULTS

The study included 1239 eligible participants, comprising 840 non-shift workers and 399 shift workers (148 with SWSD and 251 without SWSD). Compared to non-shift working males, those involved in shift work (β 1.58, 95% CI 0.75 - 2.42, p < 0.001) and those suffering from SWSD (β 2.86, 95% CI 1.86 - 3.85, p < 0.001) they had significantly higher PEDT scores. Additionally, we identified daily sleep of less than six hours, depression, anxiety, diabetes, hyperlipidemia, frequent alcohol consumption (more than twice a week), and erectile dysfunction as risk factors for PE. The predictive model for PE demonstrated commendable efficacy.

CONCLUSION

Both shift work and SWSD significantly increase the risk of premature ejaculation, with the risk magnifying in tandem with the duration of shift work. This study reveals the potential impact of shift work and SWSD on PE and provides new theoretical foundations for the risk assessment and prevention of this condition.

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.

Vital function of DRD4 in dapoxetine medicated premature ejaculation treatment

BACKGROUND

Recently, dapoxetine has been widely accepted to treat premature ejaculation by fast-inhibiting 5-hydroxytryptamine reuptake. However, dapoxetine is not suitable for all premature ejaculation patients in clinical treatment. We need to investigate and reveal the mechanism deeply to solve this problem.

OBJECTIVES

To investigate and reveal the function of dopamine D4 receptor in dapoxetine medicated premature ejaculation treatment.

MATERIALS AND METHODS

A rat model was used to screen rapid ejaculators. The molecular mechanisms of histone serotonylation-mediated regulation of dopamine D4 receptor were demonstrated by chromatin immunoprecipitation, DNA pull-down, mass spectrometry analysis, and coimmunoprecipitation experiments. The biological function of dopamine D4 receptor was investigated through in vivo experiments by intrathecal injection of shDRD4 to knockdown dopamine D4 receptor.

RESULTS

In this study, we found that dapoxetine increased expression of 5-hydroxytryptamine and dopamine D4 receptor. We demonstrated that dapoxetine increased levels of 5-hydroxytryptamine, which promoted histone serotonylation (H3K4me3Q5ser) and transcription factor myeloid zinc-finger 1 complex binding on the dopamine D4 receptor promoter, upregulated the expression of dopamine D4 receptor and thus delayed ejaculation.

DISCUSSION

In this study, we demonstrated that dapoxetine increased the levels of 5-hydroxytryptamine, which promoted histone serotonylation and myeloid zinc-finger 1 complex binding to the dopamine D4 receptor promoter and upregulated the expression of dopamine D4 receptor, thus delaying ejaculation.

CONCLUSION

It is a novel mechanism that dapoxetine take effect of premature ejaculation treatment through upregulating the dopamine D4 receptor, which indicated that upregulated dopamine D4 receptor would enhance the dapoxetine effect in premature ejaculation treatment. This may lead to the development of novel therapeutic interventions for premature ejaculation.

Molecular Mechanisms of the Melatonin Receptor Pathway Linking Circadian Rhythm to Type 2 Diabetes Mellitus

Night-shift work and sleep disorders are associated with type 2 diabetes (T2DM), and circadian rhythm disruption is intrinsically involved. Studies have identified several signaling pathways that separately link two melatonin receptors (MT1 and MT2) to insulin secretion and T2DM occurrence, but a comprehensive explanation of the molecular mechanism to elucidate the association between these receptors to T2DM, reasonably and precisely, has been lacking. This review thoroughly explicates the signaling system, which consists of four important pathways, linking melatonin receptors MT1 or MT2 to insulin secretion. Then, the association of the circadian rhythm with MTNR1B transcription is extensively expounded. Finally, a concrete molecular and evolutionary mechanism underlying the macroscopic association between the circadian rhythm and T2DM is established. This review provides new insights into the pathology, treatment, and prevention of T2DM.

Ejaculatory Duct Obstruction Affects Seminal Vesicle Contractile Efficacy and Smooth Muscle Ultrastructure in a Rat Model

The purpose of this study was to investigate the effects of ejaculatory duct obstruction (EDO) on contractile efficacy, smooth muscle ultrastructure, and α1A and M3 receptors of rat seminal vesicles (SVs). A total of 48 male rats, aged 14-15 weeks, were randomly divided into three groups, namely, the control, complete EDO, and partial EDO. SV tissues were collected at 4 and 8 weeks postoperatively for further experiments. Results revealed a marked reduction in SV contractile efficacy over time following obstruction in the complete EDO group. The contractile force and frequency decreased and increased in the partial EDO group at week 4, respectively, whereas contractile efficacy significantly reduced at week 8. Moreover, obstruction resulted in significant downregulation in expression of α1A and M3 proteins and mRNAs in rats from the complete EDO group over time. Rats in the partial EDO group initially exhibited an increase followed by a decrease. Analysis of the ultrastructure of SV smooth muscles confirmed the above changes. In conclusion, complete EDO can lead to a progressive decrease in contractile efficiency of SVs. On the other hand, partial EDO can first compensate for the contraction of SVs and gradually decompensate afterwards.

The role of tyrosine hydroxylase within dapoxetine-assisted therapy against premature ejaculation

BACKGROUND

There are several investigations that have revealed that cerebral dopamine (DA) plays a pivotal role in the occurrence of premature ejaculation (PE). Although tyrosine hydroxylase (TH) is an essential enzyme for the synthesis of DA, only few investigations have described the role of TH in regulation mechanisms for ejaculation till now. To investigate whether there is a correlation between TH expression level in the brain and different ejaculation behavior in rats. Then explore whether the TH expression in the brain will change after acute dapoxetine treatment in rats with Rapid ejaculation.

METHODS AND RESULTS

Rats (male, S-D rats, 6-8 weeks) were separated into three groups based on their ejaculation frequency: Rapid, Normal, and Sluggish. Expression level of DA in the brain was determined by enzyme-linked immune sorbent assay (ELISA) kit, TH expression level in the brain was determined by immunohistochemistry and Western Blot (WB) techniques. Among the three groups, DA and TH expression level were the highest in the Rapid ejaculation group, while the lowest was the Sluggish ejaculation group. The results also showed that TH level was positively associated with ejaculation frequency (r = 0.8038, P < 0.001) and negatively associated with ejaculation latency (r=-0.6199, P = 0.018). Furthermore, acute dapoxetine therapy in rats with Rapid ejaculation downregulated TH level in the brain.

CONCLUSION

Changes in ejaculation behavior were significantly linked with TH level. Upregulated TH in selected brain regions related with ejaculation could cause rapid ejaculation. The effect of dapoxetine in prolonging ejaculation could be related to TH downregulation within the brain.

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.

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.

Endogenous Deficiency of Brain-Derived Neurotrophic Factor Induces the Downregulation of Tryptophan Hydroxylase-2 Expression in Raphe Nuclei of Rapid Ejaculator Rats

BACKGROUND

Premature ejaculation (PE) is one of the most common ejaculatory disorders. Recent studies have suggested a close relationship between the serotonin (5-hydroxytryptamine [5-HT]) system and brain-derived neurotrophic factor (BDNF), raising the question of whether BDNF plays a role in ejaculation regulation. To our knowledge, no previous studies have explored BDNF level of the central nervous system in ejaculatory disorders. At the same time, the interaction of central BDNF and 5-HT systems has not been undertaken in ejaculation regulation field.

AIM

The aim of this study was to investigate the interaction between BDNF and 5-HT levels in raphe nuclei which contains the serotonergic neurons in a rat animal model with different ejaculatory behavior.

METHODS

Eighteen male rats were selected and classified as "sluggish," "normal," and "rapid" ejaculators on the basis of ejaculation frequency during copulatory behavioral testing. BDNF and 5-HT levels were determined by enzyme-linked immunosorbent assay (ELISA). Real-Time Quantitative PCR and Western blot analyses were used to measure the mRNA level of Tryptophan Hydroxylase-2 (TPH2) gene and the expression of TPH2 protein (the rate-limiting enzyme in central 5-HT synthesis) in raphe nuclei, respectively.

OUTCOMES

Male rat sexual behavior, the levels of BDNF and 5-HT in raphe nuclei of rats with different ejaculatory behavior, the mRNA level of gene encoding TPH2 and the expression of TPH2 protein in raphe nuclei.

RESULTS

The primary finding of our study was that BDNF concentration was significantly decreased in raphe nuclei of rapid ejaculators. There was a strong positive correlation between the levels of BDNF and 5-HT (r = 0.944, P < .001). Further results showed that decreased TPH2 gene expression accompanied by TPH2 protein was shown in rapid ejaculators with lower BDNF level.

CLINICAL IMPLICATIONS

With refinement of current knowledge, BDNF may eventually serve as a promising biomarker in patients with PE.

STRENGTHS & LIMITATIONS

There are no previous studies examining the interaction of the brain BDNF and 5-HT in ejaculation regulation field. The main limitation is the limited sample size.

CONCLUSION

BDNF may act via increasing the synthesis of central 5-HT in the process of ejaculation regulation. Our results suggest lack of endogenous BDNF induces the downregulation of TPH2 gene expression and the decrease of 5-HT synthesis in raphe nuclei of rapid ejaculator rats.