Direct evidence of facilitative actions of dopamine in the medial preoptic area on reflexive and noncontact erections in male rats

Neurophysiology of male sexual arousal-Behavioral perspective

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

Effect of prescription medications on erectile dysfunction

Erectile dysfunction (ED) affects about 50% of men in the USA and is primarily attributed to physiological (organic) and psychological causes. However, a substantial portion of men suffer from ED due to iatrogenic causes. Common medications such as antihypertensives, non-steroidal anti-inflammatory drugs and antacids may cause ED. Physicians should be aware of the various prescription medications that may cause ED to properly screen and counsel patients on an issue that many may feel too uncomfortable to discuss. In this review, we discuss the physiology, data and alternative therapies for the ED caused by medications.

The Impact of Illicit Use of Amphetamine on Male Sexual Functions

INTRODUCTION

Data concerning the impact of amphetamine on male sexual functions are limited, although amphetamine has been used as an aphrodisiac.

AIMS

This cross-sectional study was to assess the impact of illicit use of amphetamine on male sexual functions.

METHODS

Male illicit drug users in a Drug Abstention and Treatment Center were recruited to complete a self-administered questionnaire, and data were compared with age-matched controls.

MAIN OUTCOME MEASURES

The International Index of Erectile Function (IIEF) and global assessment questions were used to assess sexual functions.

RESULTS

Of 1,159 amphetamine mono-illicit drug users, the mean age was 31.9 ± 7.5 (18-57) years, and mean duration of drug use was 30.7 ± 52.2 (median 9, range 0.1-252) months. Half of them reported that drug use had no impact on their sexual functions. The other half reported drug impacts as reduced erectile rigidity and sexual life satisfaction, enhanced orgasmic intensity, and prolonged ejaculation latency time more often than the opposite effects, while they reported enhanced or reduced effect equally on sexual desire. Dosing frequency of amphetamine was associated with its impact on sexual functions, but duration of its use had little association with that. Compared with 211 age-matched controls, the amphetamine mono-illicit drug users had lower IIEF scores in the domains of erectile function, orgasmic function, and overall satisfaction, but there are no significant differences in intercourse satisfaction and sexual desire scores. The prevalence of erectile dysfunction (ED) was significantly higher in the drug users than in the controls (29.3% vs. 11.9%). The odds ratio of ED for amphetamine use was 2.1 (95% confidence interval 1.2-3.6) after adjustment for other risk factors.

CONCLUSIONS

The impact of illicit use of amphetamine on male sexual functions varied among users, and their ED prevalence was higher than the controls.

Effects of bupropion on the ejaculatory response of male rats

Chronic antidepressant treatment is associated with sexual side effects, particularly affecting the ejaculatory response. Bupropion (BP), an antidepressant inhibiting dopamine/noradrenaline reuptake, seems to have a low impact upon male sexual function. Ejaculation is regulated both at the brain and spinal cord by the spinal generator for ejaculation (SGE). We investigated the effects of chronic BP treatment on ejaculatory behavior and on SGE functioning. Sexually experienced male rats were intraperitoneally (i.p.) injected with BP (7.5 or 15 mg kg(-1)) during 14 days and tested for sexual behavior on days 1, 7 and 14 of treatment; these same males were used to evaluate the functioning of the SGE by recording the genital motor pattern for ejaculation (GMPE). Acute and chronic BP administration did not importantly modify copulatory behavior of male rats. Chronic treatment with the low dose of BP produced deficits in the functioning of the SGE that were restored by activation of the SGE through afferent stimulation. Conversely, chronic treatment with the high-dose of BP disrupted the functioning of the SGE, as the deficits were not compensated by activating the SGE through sensory stimulation. It is concluded that chronic BP at high doses alters the functioning of the SGE.

Sexual side effects of serotonergic antidepressants: mediated by inhibition of serotonin on central dopamine release?

Antidepressant-induced sexual dysfunction adversely affects the quality of life of antidepressant users and reduces compliance with treatment. Animal models provide an instructive approach for examining potential sexual side effects of novel drugs. This review discusses the stability and reproducibility of our standardized test procedure that assesses the acute, subchronic and chronic effects of psychoactive compounds in a 30 minute mating test. In addition, we present an overview of the effects of several different (putative) antidepressants on male rat sexual behavior, as tested in our standardized test procedure. By comparing the effects of these mechanistically distinct antidepressants (paroxetine, venlafaxine, bupropion, buspirone, DOV 216,303 and S32006), this review discusses the putative mechanism underlying sexual side effects of antidepressants and their normalization. This review shows that sexual behavior is mainly inhibited by antidepressants that increase serotonin neurotransmission via blockade of serotonin transporters, while those that mainly increase the levels of dopamine and noradrenaline are devoid of sexual side effects. Those sexual disturbances cannot be normalized by simultaneously increasing noradrenaline neurotransmission, but are normalized by increasing both noradrenaline and dopamine neurotransmission. Therefore, it is hypothesized that the sexual side effects of selective serotonin reuptake inhibitors may be mediated by their inhibitory effects on dopamine signaling in sex brain circuits. Clinical development of novel antidepressants should therefore focus on compounds that simultaneously increase both serotonin and dopamine signaling.

Ginkgo biloba extract treatment increases noncontact erections and central dopamine levels in rats: role of the bed nucleus of the stria terminalis and the medial preoptic area

RATIONALE

Penile erection is necessary for successful copulation in males. The extract of Ginkgo biloba leaves (EGb 761) significantly facilitates copulation in male rats, but the effect of EGb 761 on noncontact erection (NCE) remains unknown.

OBJECTIVE

The present study was conducted to evaluate the influence of EGb 761 on NCE in male rats.

MATERIALS AND METHODS

Adult Long-Evans male rats were treated with 50 mg/kg of EGb 761 (experimental group) or distilled water (control group) by gavage for 14 days. The NCE test was carried out after 14 days of EGb 761 treatment, and the latency and the numbers of NCE were recorded. Approximately 14 h following the NCE behavioral tests, animals were sacrificed by means of decapitation, and levels of dopamine in the bed nucleus of the stria terminalis (BNST) and medial preoptic area (MPOA) were measured by means of high-pressure liquid chromatography with electrochemical detection.

RESULTS

Chronic treatment with EGb 761 significantly decreased the NCE latency, but increased the number of NCEs and the dopamine levels in the BNST and MPOA in rats compared to the controls.

CONCLUSION

Treatment with EGb 761 increased both NCEs and the dopamine contents in the BNST and the MPOA. These results suggest that enhanced NCEs in the rats administered with EGb 761 may be related to dopaminergic activity in the BNST and MPOA.

Penile erection and micturition events triggered by electrical stimulation of the mesopontine tegmental area

The cholinergic neurons in the laterodorsal tegmental nucleus (LDT) play a crucial role in the regulation of rapid eye movement (REM) sleep. Because penile erection occurs during REM sleep, the involvement of the LDT in penile erection was examined in unanesthetized head-restrained rats. To detect penile erection, corpus spongiosum of the penis (CSP) pressure was measured through a telemetric device with simultaneous bulbospongiosum (BS) muscle EMG recording through stainless wires. Electrical stimulation in and around the LDT induced the following three CSP pressure patterns: 1) a full erection pattern indistinguishable from the nonevoked or spontaneous erection, characterized by a slow increase in CSP pressure with additional sharp CSP peaks associated with BS muscle bursts, 2) a muscular pattern characterized by sharp CSP pressure peaks but in the absence of a vascular component, i.e., without an increase in baseline CSP pressure, and 3) a mixed-type response characterized by high-frequency CSP pressure peaks followed by a full erection response. Full erections were evoked in and around the LDT, including more medially and ventrally. The sites for inducing mixed-type events were intermingled with the sites that triggered full erections in the anterior half of the LDT, whereas they were separated in the posterior half. The sites for muscular responses were lateral to the sites for full erections. Finally, a CSP pressure response identical to micturition was evoked in and around the Barrington's nucleus and in the dorsal raphe nucleus. These results suggest that the LDT and surrounding region are involved in the regulation of penile erection. Moreover, different anatomical areas in the mesopontine tegmentum may have specific roles in the regulation of penile erection and micturition.

Multi-target strategies for the improved treatment of depressive states: Conceptual foundations and neuronal substrates, drug discovery and therapeutic application

Major depression is a debilitating and recurrent disorder with a substantial lifetime risk and a high social cost. Depressed patients generally display co-morbid symptoms, and depression frequently accompanies other serious disorders. Currently available drugs display limited efficacy and a pronounced delay to onset of action, and all provoke distressing side effects. Cloning of the human genome has fuelled expectations that symptomatic treatment may soon become more rapid and effective, and that depressive states may ultimately be "prevented" or "cured". In pursuing these objectives, in particular for genome-derived, non-monoaminergic targets, "specificity" of drug actions is often emphasized. That is, priority is afforded to agents that interact exclusively with a single site hypothesized as critically involved in the pathogenesis and/or control of depression. Certain highly selective drugs may prove effective, and they remain indispensable in the experimental (and clinical) evaluation of the significance of novel mechanisms. However, by analogy to other multifactorial disorders, "multi-target" agents may be better adapted to the improved treatment of depressive states. Support for this contention is garnered from a broad palette of observations, ranging from mechanisms of action of adjunctive drug combinations and electroconvulsive therapy to "network theory" analysis of the etiology and management of depressive states. The review also outlines opportunities to be exploited, and challenges to be addressed, in the discovery and characterization of drugs recognizing multiple targets. Finally, a diversity of multi-target strategies is proposed for the more efficacious and rapid control of core and co-morbid symptoms of depression, together with improved tolerance relative to currently available agents.

Animal models in urological disease and sexual dysfunction

There are several conditions associated with dysfunction of the lower urinary tract or which result in a reduction in the ability to engage in satisfactory sexual function and result in significant bother to sufferers, partners and/or carers. This review describes some of the animal models that may be used to discover safe and effective medicines with which to treat them. While alpha adrenoceptor antagonists and 5-alpha-reductase inhibitors deliver improvement in symptom relief in benign prostatic hyperplasia sufferers, the availability of efficacious and well-tolerated medicines to treat incontinence is less well served. Stress urinary incontinence (SUI) has no approved medical therapy in the United States and overactive bladder (OAB) therapy is limited to treatment with muscarinic antagonists (anti-muscarinics). SUI and OAB are characterised by high prevalence, a growing ageing population and a strong desire from sufferers and physicians for more effective treatment options. High patient numbers with low presentation rates characterizes sexual dysfunction in men and women. The introduction of Viagra in 1998 for treating male erectile dysfunction and the success of the phosphodiesterase type 5 inhibitor class (PDE5 inhibitor) have indicated the willingness of sufferers to seek treatment when an effective alternative to injections and devices is available. The main value of preclinical models in discovering new medicines is to predict clinical outcomes. This translation can be established relatively easily in areas of medicine where there are a large number of drugs with different underlying pharmacological mechanisms in clinical usage. However, apart from, for example, the use of PDE5 inhibitors to treat male erectile dysfunction and the use of anti-muscarinics to treat OAB, this clinical information is limited. Therefore, current confidence in existing preclinical models is based on our understanding of the biochemical, physiological, pathophysiological and psychological mechanisms underlying the conditions in humans and how they are reflected in preclinical models. Confidence in both the models used and the pharmacological data generated is reinforced if different models of related aspects of the same disorder generate confirmatory data. However, these models will only be fully validated in retrospect once the pharmacological agents they have helped identify are tested in humans.

Dopamine and serotonin: influences on male sexual behavior

Steroid hormones regulate sexual behavior primarily by slow, genomically mediated effects. These effects are realized, in part, by enhancing the processing of relevant sensory stimuli, altering the synthesis, release, and/or receptors for neurotransmitters in integrative areas, and increasing the responsiveness of appropriate motor outputs. Dopamine has facilitative effects on sexual motivation, copulatory proficiency, and genital reflexes. Dopamine in the nigrostriatal tract influences motor activity; in the mesolimbic tract it activates numerous motivated behaviors, including copulation; in the medial preoptic area (MPOA) it controls genital reflexes, copulatory patterns, and specifically sexual motivation. Testosterone increases nitric oxide synthase in the MPOA; nitric oxide increases basal and female-stimulated dopamine release, which in turn facilitates copulation and genital reflexes. Serotonin (5-HT) is primarily inhibitory, although stimulation of 5-HT(2C) receptors increases erections and inhibits ejaculation, whereas stimulation of 5-HT(1A) receptors has the opposite effects: facilitation of ejaculation and, in some circumstances, inhibition of erection. 5-HT is released in the anterior lateral hypothalamus at the time of ejaculation. Microinjections of selective serotonin reuptake inhibitors there delay the onset of copulation and delay ejaculation after copulation begins. One means for this inhibition is a decrease in dopamine release in the mesolimbic tract.

Has dopamine a physiological role in the control of sexual behavior? A critical review of the evidence

The role of dopaminergic systems in the control of sexual behavior has been a subject of study for at least 40 years. Not surprisingly, reviews of the area have been published at variable intervals. However, the earlier reviews have been summaries of published research rather than a critical analysis of it. They have focused upon the conclusions presented in the original research papers rather than on evaluating the reliability and functional significance of the data reported to support these conclusions. During the last few years, important new knowledge concerning dopaminergic systems and their behavioral functions as well as the possible role of these systems in sexual behavior has been obtained. For the first time, it is now possible to integrate the data obtained in studies of sexual behavior into the wider context of general dopaminergic functions. To make this possible, we first present an analysis of the nature and organization of sexual behavior followed by a summary of current knowledge about the brain structures of crucial importance for this behavior. We then proceed with a description of the dopaminergic systems within or projecting to these structures. Whenever possible, we also try to include data on the electrophysiological actions of dopamine. Thereafter, we proceed with analyses of pharmacological data and release studies, both in males and in females. Consistently throughout this discussion, we make an effort to distinguish pharmacological effects on sexual behavior from a possible physiological role of dopamine. By pharmacological effects, we mean here drug-induced alterations in behavior that are not the result of the normal actions of synaptically released dopamine in the untreated animal. The conclusion of this endeavor is that pharmacological effects of dopaminergic drugs are variable in both males and females, independently of whether the drugs are administered systemically or intracerebrally. We conclude that the pharmacological data basically reinforce the notion that dopamine is important for motor functions and general arousal. These actions could, in fact, explain most of the effects seen on sexual behavior. Studies of dopamine release, in both males and females, have focused on the nucleus accumbens, a structure with at most a marginal importance for sexual behavior. Since accumbens dopamine release is associated with all kinds of events, aversive as well as appetitive, it can have no specific effect on sexual behavior but promotes arousal and activation of non-specific motor patterns. Preoptic and paraventricular nucleus release of dopamine may have some relationship to mechanisms of ejaculation or to the neuroendocrine consequences of sexual activity or they can be related to other autonomic processes associated with copulation. There is no compelling indication in existing experimental data that dopamine is of any particular importance for sexual motivation. There is experimental evidence showing that it is of no importance for sexual reward.