Microinjection of the preferential dopamine receptor D3 agonist 7-hydroxy-N,N-di-n-propylaminotetralin hydrobromide into the hypothalamic medial preoptic area induced ejaculation in anesthetized rats

Mechanism of Shugan Yidan fan, a Chinese herbal formula, in rat model of premature ejaculation

BACKGROUND

Premature ejaculation (PE) is one of the most common forms of sexual dysfunction in men, and multimodal therapeutic regimens should be considered to treat the condition. We developed a Chinese medicine herbal medicine, Shugan Yidan fang that had a significant clinical effect on PE patients, extending the time between penetration and ejaculation. However, the mechanism of this formula remains unclear. There is evidence that PE is associated with peripheral neuropathology, and the actions of dopamine (DA) and 5-hydroxytryptamine (5-HT). The aim of this study was to investigate the mechanism of Shugan Yidan fang's effect on PE through the relationship between sexual behavioristics and the level of neurotransmitters and dopamine receptors (DARs).

RESULTS

We showed that the male PE groups had a significant PE phenotype compared to healthy rats. Treatment with Shugan Yidan fang improved the behavioristics of the PE rats, and reduced the expression of DAR mRNA and protein while improving dopamine transporter levels.

CONCLUSIONS

Our study provided evidence for the beneficial effect of Shugan Yidan fang in PE therapy, and proposed a preliminary potential mechanism for the clinical application of the formula.

Medial preoptic estrogen receptor-beta blunts the estrogen receptor-alpha mediated increases in wheel-running behavior of female rats

Estrogens are believed to enhance rodent voluntary wheel-running through medial preoptic (mPOA) estrogen receptor α (ERα) signaling, with little role attributed to estrogen receptor β (ERβ). Systemic ERβ activation has been shown to mitigate ERα driven increases in wheel-running. Therefore, the present goal was to determine whether ERβ signaling in the mPOA plays a similar modulatory role over ERα. We utilized outbred wild-type (WT) and rats selectively bred for low voluntary running (LVR) behavior to address whether mPOA ERβ signaling blunts ERα driven wheel-running behavior and immediate-early gene (Fos, Zif268, and Homer1) mRNA induction. Further, we addressed baseline mPOA mRNA expressions and circulating 17β-estradiol levels between female WT and LVR rats. Following ovariectomy, WT rats reduced running behavior ∼40 %, with no effect in LVR rats. Intra-medial preoptic injection of the ERα-agonist propylpyrazoletriol (PPT) increased wheel-running ∼3.5-fold in WT rats, while injections of the ERβ-agonist diarylpropionitrile (DPN) or a combination of the two agonists had no effect. Similarly, ERα-agonism (PPT) increased Fos and Homer1 induction ∼3-fold in WT and LVR isolated mPOA neurons, with no effect of the ERβ-agonist DPN alone or in combination with PPT, suggesting medial-preoptic ERβ activity may blunt ERα signaling. LVR rats exhibited higher mPOA mRNA expressions of Esr1, Esr2 and Cyp19a1, lower normalized uterine wet weights and lower 17β-estradiol plasma levels compared to WT, suggesting their low running may be due to low circulating estrogen levels. Collectively, these findings highlight mPOA ERβ as a potential neuro-molecular modulator of the estrogenic control of wheel-running behavior.

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

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

Effects of the dopamine D3 receptor agonist 7-hydroxy-2-(di-N-propylamino) tetralin in hyperthyroidism-induced premature ejaculation rat model

Various factors are involved in the aetiology of premature ejaculation (PE). Hyperthyroidism is one of the causes of acquired PE, but the exact mechanism by which it causes the disorder is not yet understood. The aim of this study was to evaluate the role of the dopaminergic system in hyperthyroidism-induced PE by the intracerebroventricular microinjection of the preferentially active dopamine receptor agonist 7-hydroxy-2-(di-N-propylamino) tetralin (7-OH-DPAT) in a rat model of this disorder. Wistar rats were randomly divided into hyperthyroid and control groups, and ejaculation was induced by the ICV administration of 7-OH-DPAT. To evaluate the emission and expulsion phases of ejaculation, measurements of seminal vesicle pressure (SVP) and electromyographic recordings of the bulbospongiosus muscle were taken. The interval between the 7-OH-DPAT administration and the first ejaculation was significantly less in the hyperthyroid group (p < .01) than in the control group, and the maximum amplitude of the SVP values revealed a statistically significant difference between the groups (p < .01). The intervals between contractions of the seminal vesicle and bulbospongiosus muscles were also significantly less in the hyperthyroid group (p = .0187) than in the control group. No other results differed significantly between the groups. This study determined that hyperthyroidism altered only the emission phase of ejaculation.

Guibourtia tessmannii-induced fictive ejaculation in spinal male rat: involvement of D1, D2-like receptors

CONTEXT

Guibourtia tessmannii (Caesalpiniaceae) is a plant traditionally used as aphrodisiac. We previously reported the pro-ejaculatory effects of the aqueous and methanol extracts of G. tesmannii in spinal male rat. However, the mechanism underlying such effects has not been elucidated.

OBJECTIVE

This study characterizes the dopaminergic sub-type receptors involved in G. tesmannii-induced ejaculation in male Wistar rat.

MATERIALS AND METHODS

Urethane-anesthetized spinal male rats were intravenously treated with saline solution (1 mL/kg, control); dopamine (0.1 μmol/kg, reference); aqueous or methanol extracts of G. tesmannii (20 mg/kg) in the absence or presence of haloperidol (0.26 μmol/kg), a nonspecific dopaminergic receptor antagonist, Sch23390 (0.26 μmol/kg), a specific D1-like receptor antagonist or, sulpiride (0.26 μmol/kg), a specific D2-like receptor antagonist. Electromyography of the bulbospongiosus muscles and intraseminal pressure were recorded after urethral, penile and drug stimulations.

RESULTS

Urethral and penile stimulations, intravenous injection of dopamine or, aqueous and methanol extracts of G. tesmannii always triggered the expression of rhythmic contraction of the bulbospongiosus muscles with an average mean of 3.33 ± 0.43; 7.83 ± 0.85; 9.80 ± 0.86; 0.83 ± 0.54 and 2.67 ± 0.95 contractions, respectively. The intraseminal pressure was more expressed after urethral and penile stimulations (15.66 ± 1.58 and 13.60 ± 2.40 mmHg, respectively). In rats pretreated with haloperidol, Sch23390 or sulpiride, no ejaculation was recorded after intravenous injection of G. tesmannii extracts or dopamine.

DISCUSSION AND CONCLUSION

Guibourtia tesmannii-induced ejaculation requires the integrity of D1 and D2-like receptors. These findings further justify the ethno-medicinal claims of G. tesmannii as an aphrodisiac.

The drug treatment of delayed ejaculation

Delayed ejaculation (DE) is an uncommon and a challenging disorder to treat. It is often quite concerning to patients and it can affect psychosocial well-being. Here we reviewed how DE is treated pharmacologically .We also highlighted specific settings where drugs could be introduced to medical practice. Electronic databases were searched from 1966 to February 2016, including PubMed MEDLINE, EMBASE, EBCSO Academic Search Complete, Cochrane Systematic Reviews Database, and Google Scholar using key words; delayed ejaculation, retarded ejaculation, inhibited ejaculation, drugs, treatment, or pharmacology. To achieve the maximum sensitivity of the search strategy and to identify all studies, we combined “delayed ejaculation” as Medical Subject Headings (MeSH) terms or keywords with each of “testosterone” or “cabergoline” or “bupropion” or “amantadine” or “cyproheptadine” or “midodrine” or “imipramine” or “ephedrine” or “pseudoephedrine” or “yohimbine” or “buspirone” or “oxytocin” or “bethanechol” as MeSH terms or keywords. There are a number of drugs to treat patients with DE including: testosterone, cabergoline, bupropion, amantadine, cyproheptadine, midodrine, imipramine, ephedrine, pseudoephedrine, yohimbine, buspirone, oxytocin, and bethanechol. Although there are many pharmacological treatment options, the evidence is still limited to small trials, case series or case reports. Review of literature showed that evidence level 1 (Double blind randomized clinical trial) studies were performed with testosterone, oxytocin, buspirone or bethanechol treatment. It is concluded that successful drug treatment of DE is still in its infancy. The clinicians need to be aware of the pathogenesis of DE and the pharmacological basis underlying the use of different drugs to extend better care for these patients. Various drugs are available to address such problem, however their evidence of efficacy is still limited and their choice needs to be individualized to each specific case.

Normal male sexual function: emphasis on orgasm and ejaculation

Orgasm and ejaculation are two separate physiological processes that are sometimes difficult to distinguish. Orgasm is an intense transient peak sensation of intense pleasure creating an altered state of consciousness associated with reported physical changes. Antegrade ejaculation is a complex physiological process that is composed of two phases (emission and expulsion), and is influenced by intricate neurological and hormonal pathways. Despite the many published research projects dealing with the physiology of orgasm and ejaculation, much about this topic is still unknown. Ejaculatory dysfunction is a common disorder, and currently has no definitive cure. Understanding the complex physiology of orgasm and ejaculation allows the development of therapeutic targets for ejaculatory dysfunction. In this article, we summarize the current literature on the physiology of orgasm and ejaculation, starting with a brief description of the anatomy of sex organs and the physiology of erection. Then, we describe the physiology of orgasm and ejaculation detailing the neuronal, neurochemical, and hormonal control of the ejaculation process.

Anatomy and physiology of genital organs - men

Male sexual functions involve a number of organs and structures in genitalia whose role is to produce fertilizing gametes and to allow female-partner insemination. The testes belong to the reproductive and endocrine systems as they synthesize spermatozoa and androgens, and are under finely regulated hormonal control by the hypothalamopituitary axis. Sexual responses are controlled by a complex and coordinated interplay of both the somatic and the autonomic nervous system in multiple components of the brain, spinal cord, and relevant peripheral organs. Erectile bodies are an essential element of the penis and engorgement of the penis with blood leads to penile tumescence. Blood engorgement is due to relaxation of smooth-muscle cells of erectile tissue and endothelium of the penile arteries. The penis gains additional rigidity when the ischiocavernosus muscles contract. Stimuli from peripheral and/or central origins activate particular spinal nuclei, causing penile erection. Ejaculation consists of two phases, emission and expulsion, which correspond, respectively, to secretion of the different components of the semen by sex glands and forceful expulsion of semen due to rhythmic contractions of the bulbospongiosus muscle. A spinal generator of ejaculation integrates genital stimuli and sexual cues and, when the excitatory threshold is reached, triggers ejaculation by orchestrating the activation of autonomic and somatic pathways commanding the peripheral events of ejaculation.

Inhibition of ejaculation by the non-peptide oxytocin receptor antagonist GSK557296: a multi-level site of action

BACKGROUND AND PURPOSE

Oxytocin (OT) plays a major role in the control of male sexual responses. Notably, blockade of OT receptors has been reported to inhibit ejaculation in animals. The study aimed to investigate the action of a highly selective, non-peptide OT antagonist GSK557296 in a model of pharmacologically induced ejaculation in anaesthetized rats. The site of action was assessed by investigating different delivery routes for this compound.

EXPERIMENTAL APPROACH

Urethane-anaesthetized Wistar rats were implanted with a cerebral ventricle cannula for i.c.v. injections or with a subdural catheter for intrathecal (i.t.) GSK557296 injections. Occurrence of ejaculation was assessed following i.v. 7-hydroxy-2-(di-N-propylamino)tetralin (7-OH-DPAT), a dopamine D3 receptor agonist. In addition, seminal vesicle pressures (SVP) and bulbospongiosus muscle (BS) EMG were recorded as physiological markers of emission and expulsion phases of ejaculation respectively.

KEY RESULTS

Highest i.v. GSK557296 dose reduced occurrence of ejaculation and increases in SVP but had no effect on BS-EMG. I.c.v. GSK557296 dose dependently inhibited ejaculation, increases in SVP and BS contractions. At spinal thoracic level, GSK557296 dose dependently inhibited ejaculation and increases in SVP but BS-EMG was impaired only with the highest dose. When delivered at lumbar level, GSK557296 dose dependently inhibited ejaculation, increases in SVP and BS contractions.

CONCLUSIONS AND IMPLICATIONS

In the 7-OH-DPAT-induced ejaculation model, GSK557296 acts peripherally and centrally to inhibit ejaculation with different modalities. Blockade of brain OT receptors seems to be the most effective mechanism of action. Targeting central OT receptors with highly selective antagonist seems a promising approach for the treatment of premature ejaculation.

Dopamine D3 receptor antagonists: a patent review (2007 - 2012)

INTRODUCTION

The synthesis and characterization of new highly potent and selective dopamine (DA) D3 receptor antagonists has permitted to characterize the role of the DA D3 receptor in the control of drug-seeking behavior and in the pathophysiology of impulse control disorders and schizophrenia.

AREAS COVERED

In the present review, the authors will first describe most recent classes of DA D3 receptor antagonists by reviewing about 43 patent applications during the 2007 - 2012 period; they will then outline the biological rationale in support of the use of selective DA D3 receptor antagonists in the treatment of drug addiction, impulse control disorders and schizophrenia.

EXPERT OPINION

The strongest clinical application and potential for selective DA D3 receptor antagonists lies in the reduction of drug-induced incentive motivation, the attenuation of drug's rewarding efficacy and the reduction in reinstatement of drug-seeking behavior triggered either by re-exposure to the drug itself, re-exposure to environmental cues that had been previously associated with drug-taking behavior or stress. The selectivity of these antagonists together with reduced lipophilicity (minimizing unspecific binding), increased brain penetration and improved physico-chemical profile are all key factors for clinical efficacy and safety.

A pivotal role of lumbar spinothalamic cells in the regulation of ejaculation via intraspinal connections

INTRODUCTION

A population of lumbar spinothalamic cells (LSt cells) has been demonstrated to play a pivotal role in ejaculatory behavior and comprise a critical component of the spinal ejaculation generator. LSt cells are hypothesized to regulate ejaculation via their projections to autonomic and motor neurons in the lumbosacral spinal cord.

AIM

The current study tested the hypothesis that ejaculatory reflexes are dependent on LSt cells via projections within the lumbosacral spinal cord.

METHODS

Male rats received intraspinal injections of neurotoxin saporin conjugated to substance P analog, previously shown to selectively lesion LSt cells. Two weeks later, males were anesthetized and spinal cords were transected. Subsequently, males were subjected to ejaculatory reflex paradigms, including stimulation of the dorsal penile nerve (DPN), urethrogenital stimulation or administration of D3 agonist 7-OH-DPAT. Electromyographic recordings of the bulbocavernosus muscle (BCM) were analyzed for rhythmic bursting characteristic of the expulsion phase of ejaculation. In addition, a fourth commonly used paradigm for ejaculation and erections in unanesthetized, spinal-intact male rats was utilized: the ex copula reflex paradigm.

MAIN OUTCOME MEASURES

LSt cell lesions were predicted to prevent rhythmic bursting of BCM following DPN, urethral, or pharmacological stimulation, and emissions in the ex copula paradigm. In contrast, LSt cell lesions were not expected to abolish erectile function as measured in the ex copula paradigm.

RESULTS

LSt cell lesions prevented rhythmic contractions of the BCM induced by any of the ejaculatory reflex paradigms in spinalized rats. However, LSt cell lesions did not affect erectile function nor emissions determined in the ex copula reflex paradigm.

CONCLUSIONS

These data demonstrate that LSt cells are essential for ejaculatory, but not erectile reflexes, as previously reported for mating animals. Moreover, LSt cells mediate ejaculation via projections within the spinal cord, presumably to autonomic and motor neurons.

Therapeutic targets for premature ejaculation

Premature ejaculation (PE) is the most common male sexual complaint, and may exert a profound negative impact on the man's life and partnership. Using currently available treatment alternatives (e.g., selective serotonin uptake inhibitor, agents acting locally on the penis), PE can be treated in most, but not all patients. However, since long term success rates have been disappointing, and the only approved treatment so far is the short-acting selective serotonin re-uptake inhibitor dapoxetine, there is currently an intensive search for new treatment modalities. Selection of the most promising therapeutic targets from a host of current and potential candidates depends heavily on their roles in the pathophysiology of PE. Possible central nervous targets that will be discussed are serotonin transporters, and CNS receptors for 5-HT(IA) and 5-HT(1B), dopamine, oxytocin, opioids, neurokinin-1, and glutamate. Putative peripheral targets include α(1)-adrenoceptors, phosphodiestrase enzymes, Rho kinases, purinergic (P2X) receptors, and penile sensory nerves. It is clear that exploiting the full therapeutic potential of these targets will require additional basic and clinical research.

A dual physiological character for sexual function: libido and sexual pheromones

Human sexual response is a complex function involving many cerebral, spinal and peripheral aspects; the last are relatively known and benefit from good pharmacological control, as in the case of erectile dysfunction. Spinal cord sexual reflexes also have a good theoretical and experimental description. There is minimal understanding of the cerebral sexual processes (libido, sexual arousal, orgasm). The initial perspective was that the cerebral areas implied in sexuality exert descending stimulatory and inhibitory influences on spinal cord sexual centres/reflexes. This was a wrong supposition, which inhibited progress in this subject, with a considerable impact on a subject's individual and social life. A new approach to sexual function arises from the idea that simple neurological structures can support only simple functions, while a more complex function requires correspondingly complex anatomical structures. For this reason the spinal cord would not be able to realise the integration of multiple (spinal and psychosensorial) stimuli into a unique and coherent ejaculation response. Consequently, all mechanisms implied in human sexuality would be cerebral processes, ejaculation reflexes ascending in evolution to the cerebral level. This new evolutionary concept was developed after 2001 in five distinct articles on the cerebral duality of sexual arousal, sexual hormones, ejaculation and serotonergic receptors. During this period other published results suggested a possible cerebral duality for sexual pheromones and libido in humans. All these dual physiological aspects are integrated in this review into one neurophysiological model, thus trying to further develop the new concepts of sexual function and perhaps relational behaviour. In conclusion, ejaculation is a dual cerebral process with arousal sensation (hormonally modulated) and libido perception (pheromonally modulated) as the afferent part. Two neurophysiological axes could exist in both men and women. In this assumption the mechanisms for libido and sexual arousal are not the only ones invoked, their correlations and implications are also suggested, perhaps critical aspects for further developments in the field.

Brain oxytocin receptors mediate ejaculation elicited by 7-hydroxy-2-(di-N-propylamino) tetralin (7-OH-DPAT) in anaesthetized rats

BACKGROUND AND PURPOSE

The involvement of the neuropeptide oxytocin in the control of male sexual responses is documented although its exact mechanisms of action, and especially the site(s) of action, are not fully delineated. In order to clarify this issue, we tested the effects of a peptide oxytocin antagonist delivered through different routes on sexual responses elicited, in anaesthetized male rats, by i.c.v. 7-hydroxy-2-(di-N-propylamino) tetralin (7-OH-DPAT), a dopamine agonist, preferentially active on D3 receptors.

EXPERIMENTAL APPROACH

Seminal vesicle pressure (SVP) and bulbospongiosus muscle (BS) electromyograms were recorded as physiological markers of emission and expulsion phases of ejaculation respectively and intracavernosal pressure (ICP) was monitored as a physiological marker of erection.

KEY RESULTS

When injected i.v., the oxytocin antagonist did not impair 7-OH-DPAT-induced SVP and ICP responses while BS burst frequency was diminished. When delivered i.c.v., the oxytocin antagonist dose-dependently inhibited occurrence of 7-OH-DPAT-induced sexual responses. When delivered intrathecally (i.t.) at the level of the 6th lumbar (L6) segment, but not the 13th thoracic (T13) segment, the oxytocin antagonist reduced the duration of BS responses and the occurrence of ejaculation without impairing ICP responses.

CONCLUSIONS AND IMPLICATIONS

Brain oxytocin receptors mediate male sexual responses elicited by i.c.v. 7-OH-DPAT in anaesthetized rats whereas L6 spinal oxytocin receptors only impair the occurrence of ejaculation. Peripheral oxytocin receptors are marginally involved in 7-OH-DPAT-induced sexual responses. These findings should be considered for the development of potential pharmacological treatment of premature ejaculation in man.