Inhibitory action of various 5-HT1B receptor agonists on rat masculine sexual behaviour

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.

Central Mechanisms of Apomorphine and m-Chlorophenylpiperazine on Synergistic Action for Ejaculation in Rats

BACKGROUND

We previously reported that the combination of the dopamine (DA) receptor agonist apomorphine and the 5-hydroxytryptamine (5-HT₂) receptor agonist m-chlorophenylpiperazine (m-CPP) in rats potently and selectively facilitates the ejaculatory response through activation of D₂-like and 5-HT_2C receptors, respectively.

AIM

The aim of this study was to clarify the target level of the proejaculatory effects induced by combination of these agonists.

METHODS

For in vivo behavioral studies, apomorphine and m-CPP were given intracerebroventricularly and intrathecally alone or in combination with either drug administered systemically. Male rats were acclimated to observational cages bedded in paper towels, and the occurrence of ex copula ejaculation was assessed by evaluating the presence and weight of ejaculatory plugs dropped from the tip of the penis to the paper towels or adhered to the tip of the penis at 30 min after drug administration. For in vitro contraction studies, seminal vesicles isolated from rats were suspended in an organ bath to test contractile responses to drug combinations, and the effects of the combined drugs on the contractile response of noradrenaline were also tested.

MAIN OUTCOME MEASURES

The presence and weight of ejaculatory plugs produced by drug-induced ejaculation and the contractile responses of the seminal vesicle were evaluated.

RESULTS

Intrathecal m-CPP (10 μg), but not intracerebroventricular m-CPP, evoked the synergistic effects on ejaculation when used in combination with systemically administered apomorphine (0.1 mg/kg, subcutaneous). Moreover, the synergy between m-CPP and apomorphine was completely abolished by the intrathecal 5-HT_2C receptor antagonist SB242084 (10 μg). Intrathecal or intracerebroventricular apomorphine (1-10 μg) evoked proejaculatory effects in combination with systemically administered m-CPP (0.3 mg/kg, intraperitoneal). The selective peripherally acting D₂-like receptor agonist carmoxirole did not evoke ejaculation when used in combination with m-CPP. Furthermore, isolated rat seminal vesicles were completely insensitive to the combination of apomorphine and m-CPP.

CONCLUSION

These results indicated that the synergistic effects of the drugs on ejaculation were induced at the central level but not at peripheral sites. Our findings also suggested that the 5-HT_2C receptor mediated the stimulation of the spinal ejaculatory pattern generator and was synergistically potentiated by the spinal DA receptor and that activation of the supraspinal DA receptor was also involved in mediating these synergistic effects. Yoshizumi M, Yonezawa A, Kimura Y, et al. Central Mechanisms of Apomorphine and m-Chlorophenylpiperazine on Synergistic Action for Ejaculation in Rats. J Sex Med 2021;18:231-239.

Cocaine-induced genital reflexes in paradoxical sleep deprived rats: Indications of mediation by serotonin receptors

As paradoxical sleep deprivation (PSD) modifies cocaine-induced genital reflexes (penile erection [PE] and ejaculation [EJ]) and since cocaine is a serotonin (5-HT) reuptake inhibitor, we hypothesized that 5-HT also plays a role in these genital reflexes in PSD male rats. After a 4-day period of PSD each group was administered with serotonergic drugs prior to cocaine and placed in observation cages. The selective 5-HT(1) agonist (8-OH-DPAT) completely abolished PE events whereas the antagonist (pindolol) did not produce significant effects in the number of animals displaying PE. It was found that both drugs reduce the frequency of PE. There were no significant effects on the number of animals that ejaculated or in its frequency after pindolol although both parameters were reduced by the agonist at the highest doses (2 and 4 mg/kg, SC). Pretreatment with the 5-HT(2) agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) (0.12; 0.5 and 1 mg/kg, SC) significantly reduced the number of rats displaying PE and all doses reduced both PE and EJ frequencies. The number of animals displaying PE after 5-HT(2) antagonist (ketanserin) pretreatment at 1 and 2.5 mg/kg doses was significantly decreased in relation to vehicle rats and all doses reduced PE frequency. 5-HT(2) compounds at any dose did not affect the number of animals ejaculating, but the frequency was significantly reduced by all doses of DOI and by 1 to 5 mg/kg doses of ketanserin. Taken together, the results suggest that serotonergic receptors play an important role in genital reflexes induced by cocaine in sleep deprived males.

Sexual Dysfunctions and Blood Hormonal Profile in Men with Focal Epilepsy

PURPOSE

To evaluate the incidence of sexual dysfunction in men with focal epilepsy and to establish their hormonal profiles.

METHODS

We prospectively analyzed sexual functions and hormone blood levels in 40 male patients (age ranged from 18 to 44 years, with an average age of 27.6+/-5.6 years) with refractory focal epilepsy. We used the Czech version of the structured questionnaire entitled International Inventory of Erectile Function (IIEF) to assess the patients' sexual functions. The subscales of this questionnaire separately evaluate erectile function (IIEF I), orgasmic function (IIEF II), sexual desire (IIEF III), intercourse satisfaction (IIEF IV), and overall satisfaction with sex life (IIEF V). In all of the patients, the following blood tests were performed: quantitative assessment of blood levels of prolactin (PRL), total testosterone (total-T), free androgen index (FAI), sexual hormone-binding globulin (SHBG), estradiol (E2), dehydroepiandrosterone sulfate (DHEAS), progesterone (PRG), follicle-stimulating hormone (FSH), and luteinizing hormone (LH). All these quantitative laboratory data were correlated with other clinical variables and with the results of the IIEF. chi2 and Wilcoxon tests were used for the statistical analysis. A p-value<0.05 was considered to be statistically significant.

RESULTS

At least one of the types of sexual dysfunction, as defined by IIEF (IIEF I, II, and III), was found in 22 (55%) of the 40 patients (55%). Erectile dysfunction (IIEF I) was found in six (15%) of 40 patients, orgasmic dysfunction (IIEF II) in six (15%) of 40 patients, and loss of sexual desire (IIEF III) in 16 (40%) of 40 patients. According to other subscales of IIEF, 22 (55%) of 40 patients were not satisfied with sexual intercourse (IIEF IV), and 20 (50%) of 40 patients were not satisfied with their sex livee (IIEF V). None of the subscales of IIEF was significantly correlated with the age of the patients or with the duration of epilepsy. In patients with at least one of the sexual dysfunctions (IIEF I, II, and III), we found a statistically significant increase of FSH and SHBG, and a decrease of DHEAS and FAI in comparison with those in the patients with normal sexual functions. In patients with erectile dysfunction, we found the same changes and a significant increase of E2. In patients with orgasmic dysfunction, we found a statistically significant decrease of DHEAS. In patients with dysfunction of sexual desire, we noticed a significant increase of SHBG and a decrease of DHEAS and FAI. All patients with orgasmic dysfunction were being treated with carbamazepine (CBZ) in monotherapy or combination therapy. In patients with at least one type of sexual dysfunction (IIEF I, II, and III), we found a higher proportion of valproate treatment in monotherapy or combination therapy in comparison with CBZ.

CONCLUSIONS

Our study showed a relatively high incidence of sexual dysfunction and dissatisfaction with sexual intercourse and sex life, as defined by the IIEF I-V questionnaire, in men with refractory focal epilepsy. The most frequent dysfunction in these patients is the impairment of sexual desire. However, our study indicates some specific hormonal changes related to various types of sexual dysfunction that are not related to antiepileptic drug treatment.

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.

Do similar neural systems subserve aggressive and sexual behaviour in male rats? Insights from c-Fos and pharmacological studies

It is a common belief that male aggressive and sexual behaviour share many of the underlying neurobiological, neurological, pharmacological and neuroendocrine mechanisms. Therefore, we studied brain activation patterns in male rat after performance of aggressive and sexual behaviour and compared serotonergic pharmacology in the same paradigms to delineate possible similarities and differences. Patterns of Fos-immunoreactivity induced by aggressive and sexual encounters of Wild-type male Brown Norway rats were studied to localise the commonly activated (functionally shared) parts of the circuitry, and the specific (functionally different) parts of the neuronal circuitry. Some brain areas (caudal medial preoptic area and medial amygdala) were commonly activated, but other areas (e.g. posterodorsal parts of the medial amygdala, rostral preoptic and premammillary hypothalamus) showed remarkably specific differences in neural activation. 5-HT(1A) receptor agonists inhibit aggressive, but stimulate male sexual behaviour, whereas 5-HT(1B) receptor agonists inhibit both types of behaviour. Selective serotonin reuptake inhibitors share comparable inhibitory effects in aggression and sexual behaviour, although only at relatively high doses. We propose that separate hard-wired neural systems exist in the brain for aggressive and sexual behaviours, modulated via hierarchically 'higher-level' brain areas that are involved in the integration (gating) of the behavioural outcome of an organism.

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.

Pharmacological and physiological aspects of sexual exhaustion in male rats

The present article reviews the current findings on the interesting phenomenon of sexual satiety. Knut Larsson in 1956 reported on the development of sexual exhaustion in the male rat after repeated copulation. We have studied the process and found the following results. (1) One day after 4 hours of ad libitum copulation, two-thirds of the population showed complete inhibition of sexual behavior, while the other third displayed a single ejaculatory series from which they did not recover. (2) Several pharmacological treatments, including 8-OH-DPAT, yohimbine, naloxone and naltrexone, reverse this sexual satiety, indicating that the noradrenergic, serotonergic and opiate systems are involved in this process. Indeed, direct neurochemical determinations showed changes in various neurotransmitters during sexual exhaustion. (3) Given enough stimulation, by changing the stimulus female, sexual satiety was prevented, suggesting that there are motivational components of the sexual inhibition that characterizes sexual exhaustion. (4) The GABA antagonist bicuculline, or the electrical stimulation of the medial preoptic area, did not reverse sexual exhaustion. These data suggest, on the one hand, that sexual exhaustion and the postejaculatory interval (which is shortened by bicuculline administration) are not mediated by similar mechanisms and, on the other, that the medial preoptic area does not regulate sexual satiety. (5) The androgen receptor density in brain areas closely related to the expression of masculine sexual behavior, such as the medial preoptic nucleus, was drastically reduced in sexually exhausted animals. Such reduction was specific to certain brain areas and was not related to changes in the levels of androgens. These results suggest that changes in brain androgen receptors account for the inhibition of sexual behavior present during sexual exhaustion. (6) The recovery process of sexual satiety after 4 hours of ad libitum copulation reveals that, after 4 days, only 63% of the males are able to show sexual behavior while after 7 days all animals display copulatory activity.

Participation of 5-HT(1B) receptors in the inhibitory actions of serotonin on masculine sexual behaviour of mice: pharmacological analysis in 5-HT(1B) receptor knockout mice

1 The role of the 5-Hydroxytryptamine(1B) (5-HT(1B)) receptor subtype in masculine sexual behaviour in mice was analysed in both 5-HT(1B) receptor knockout (KO(1B)) and wild-type (WT) animals. 2 Comparison of male copulatory behaviour of WT and KO(1B) strains revealed that KO(1B) mice become interested earlier in sexual behaviour, but require more stimulation to achieve ejaculation than its corresponding WT strain. 3 The pharmacological manipulation of male sexual activity in the WT strain showed that the serotonin precursor 5-Hydroxytryptophan (5-HTP), the 5-HT(1B) agonist (1-(m-trifluoromethylphenyl) piperazine (TFMPP) and the 5-Hydroxytryptamine(1A) (5-HT(1A)) receptor agonist 8-hydroxy-2-di-n-propylamino-tetralin (8-OH-DPAT) all inhibited male copulatory behaviour in mice. 4 In KO(1B) mice, TFMPP lacked an effect, 5-HTP exerted a mild inhibitory effect while 8-OH-DPAT provoked only a tendency towards a reduction in the percentage of animals that achieved ejaculation. In general, KO(1B) mice were less sensitive to the inhibitory actions of 5-HTP and 8-OH-DPAT than the WT strain. 5 Based on these results, we can suggest that serotonin plays a general inhibitory role in the sexual behaviour of male mice and that both 5-HT(1B) and 5-HT(1A) receptor subtypes participate in the inhibitory actions of this neurotransmitter. 6 The absence of the 5-HT(1B) receptor subtype affected both components of mouse masculine sexual behaviour, motivation and execution, further confirming the involvement of this receptor subtype in the control of this behaviour. In addition, the diminished sensitivity to serotonergic stimulation exhibited by KO(1B) mice suggests the occurrence of compensatory changes as a consequence of the absence of the 5-HT(1B) receptor subtype.

Involvement of the 5-HT(1A) and 5-HT(1B) serotonergic receptor subtypes in sexual arousal in male mice

The presence of a sexually receptive female behind a partition that prevents physical contact, but not seeing or smelling, increases blood testosterone level and induces the specific behavior in CBA male mice so that they more frequently approach the partition and spend more time near it in an attempt to make their way to the female. Treatment with the selective 5-HT(1A) serotonin receptor agonist 8-OH-DPAT (0.1, 0.25, 0.5 and 2.0 mg/kg) induced a dose-dependent decrease in the amount of time spent by the males near the partition, or "partition time", which is considered the main pattern of sexual motivation. The activating effect of female exposure on the male's pituitary-testicular system was totally blocked, as no increase in plasma testosterone level was observed. The 5-HT(1A) antagonist p-MPPI (0.1, 0.2 and 0.4 mg/kg) itself did not affect behavior or alter plasma testosterone, but attenuated the inhibiting effect of 8-OH-DPAT on behavior and totally antagonised the effect of the 5-HT(1A) agonist on testosterone response. The 5-HT(1B) agonist CGS-12066A (1.0 and 2.0 mg/kg) has no influence on the plasma testosterone increase exhibited by the male in response to female exposure. At the same time, either dose of CGS-12066A significantly reduced the partition time. The conclusion was made that the 5-HT(1A) subtype is involved in controlling both behavioral and hormonal indices of sexual arousal in male mice, while the 5-HT(1B) receptors antagonise sexual motivation, but do not modify the hypothalamic-pituitary-testicular response.

Exhaustion of the coital reflex in spinal male rats is reversed by the serotonergic agonist 8-OH-DPAT

Previous studies from our laboratory have shown that the genital motor pattern associated to the coital reflex in spinal male rats becomes exhausted when repeatedly evoked. Exhaustion of the genital motor pattern could be related to the sexual exhaustion phenomenon observed in copulating male rats. The present study was aimed to describe the features of coital reflex exhaustion and to determine if the 5-HT1A agonist 8-OH-DPAT was able to reverse exhaustion of this ejaculatory-like response. Additionally, the effect of pre-treatment with the 5-HT1A antagonist WAY 100635 on the 8-OH-DPAT induced motor response was evaluated. Results revealed that development of coital reflex exhaustion initiated with a progressive increase in the latency of response and was characterised by a change in the properties of the motor pattern itself. Once exhausted, i.v. administration of 8-OH-DPAT provoked the immediate expression of a potent motor pattern similar to the coital reflex, but in the absence of urethral stimulation. Injection of WAY 100635 induced, per se, expression of the coital reflex after exhaustion. Notwithstanding, pre-treatment with WAY 100635 was able to block the 8-OH-DPAT-induced motor response implying that its effect was exerted upon 5-HT1A receptors. Data suggest that the sexual exhaustion phenomenon might possess a spinal component.

Selectively bred male rat lines differ in naïve and experienced sexual behavior

Ejaculatory behavior is facilitated by activating 5-hydroxytryptamine(1A) (5-HT(1A)) receptors. The present study examined male sexual behavior in rat lines that were selectively bred for their different hypothermic responses to 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT). Sexual behavior was examined in naïve and experienced HDS (high 8-OH-DPAT sensitive), LDS (low 8-OH-DPAT sensitive), and RDS (randomly bred) rats lines. In addition, the effects of 8-OH-DPAT (0.05 mg/kg) and N-(2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl)-N-(2-pyridinyl)-cyclohexane-carboxamide (WAY 100,635; 1 mg/kg) were examined. Naïve HDS animals had diminished ejaculatory behavior (as indicated by a decreased number of intromissions, mounts and ejaculations, increased ejaculation and intromission latency, and longer inter-copulatory interval), compared to the LDS and RDS groups. In addition, the post-ejaculatory interval (PEI) was longer in the HDS group. With experience, the HDS group improved its ejaculatory behavior. Experienced HDS animals had a lower number of intromissions and a longer PEI compared to the LDS group. 8-OH-DPAT facilitated ejaculatory behavior in both HDS and LDS groups. This effect was more pronounced in the LDS group. WAY 100,635 did not alter sexual behavior in either group. In summary, alteration in forebrain 5-HT(1A) receptors in HDS animals may be involved in the ability of naïve rats to achieve ejaculation. 5-HT(1A) receptors are involved in the regulation of resumption of sexual behavior after ejaculation.

Brain and sexual behavior

This chapter will give personal accounts of the neural basis of male rat sexual behavior from two somewhat different perspectives, one tilted towards neuroanatomy (K.L.), and one tilted towards monoaminergic pharmacology (S.A.). Both perspectives were strongly influenced by the Zeitgeist, the former imperceptibly merging into the latter as relations between the neural substrate for monoaminergic neurotransmission was elucidated.

Effects of epilepsy on women's reproductive health

Reproductive dysfunctions are common and wide-ranging in women with epilepsy. Menstrual cycle disruption, anovulatory cycles, disturbances in hypothalamic and/or pituitary hormones, and disturbances in gonadal steroids are more common among women with epilepsy. Sexual dysfunction can present as either disorders of desire or physiologic arousal, but the most common dysfunction appears to be an inadequate initial physiologic arousal response. Reproductive dysfunctions may be due to psychologic, pharmacologic, or physiologic factors. Physicians should routinely question all women with epilepsy regarding their reproductive and sexual health. A full history, a complete physical, and laboratory evaluations with endocrinologic work-up should be performed in any woman who reports a reproductive dysfunction. Treatment and/or referral to a gynecologist or endocrinologist should be initiated as appropriate.

8-OH-DPAT and male rat sexual behavior: partial blockade by noradrenergic lesion and sexual exhaustion

As previously shown, the 5-HT1A agonist 8-OH-DPAT is a potent facilitator of male rat copulatory behavior in both sexually experienced and sexually exhausted male rats. The basis of this facilitation is still not clear. Therefore, the purpose of the present study was to determine whether 8-OH-DPAT-induced sexual-behavior facilitation could be counteracted by lesioning the NA system with the noradrenergic neurotoxin DSP4. In NA-lesioned, sexually experienced, non-exhausted rats, the facilitatory effects of 8-OH-DPAT on the number of mounts and the postejaculatory interval were reduced, the effect on the intromission latency disappeared, while the percentage of copulating rats was not significantly altered. In sexually exhausted rats bearing a lesion of the NA system, the facilitatory effects of 8-OH-DPAT on the percentage of copulating rats was blocked. Data are discussed on the basis of the interactions between the noradrenergic and serotonergic systems in the mediation of the facilitatory effect of 8-OH-DPAT in sexually exhausted and non-exhausted rats.

The inhibition of sexual behavior in male rats by propranolol is stereoselective

We have previously reported that administration of racemic mixtures of propranolol was associated with a marked inhibition of mating behavior in male rats. To compare the effects of (+)-propranolol, (-)-propranolol, and (+/-)-propranolol in sexually experienced males, rats ejaculating in four or more mating tests were divided into three groups (N = 16 per group) such that no differences in parameters of copulatory behavior were evidence in preexperimental tests. No major effect of propranolol on parameters of behavior associated with initiation of sexual behavior was evident. In contrast, other measures of behavior were profoundly modified. The ejaculatory threshold, indicated by the number of intromissions preceding ejaculation, was increased after (+)- and (+/-)-propranolol, but not (-)-propranolol. The number of mounts without intromission preceding ejaculation was increased only after (+/-)-propranolol. A decrease in copulatory efficacy was evident after (-)- or (+/-)-propranolol, but not after (+)-propranolol. Increases in ejaculation latency, intercopulatory interval, and postejaculatory interval were observed after (-)- and (+/-)-propranolol, but not after (+)-propranolol. In summary, the present data indicate that the (-) isomer of propranolol is the active form necessary for the inhibitory effects of propranolol on male sexual function. We suggest that this inhibition is due to specific receptor-mediated mechanisms, involving beta-adrenoceptors and 5-HT1A receptor interactions.

Dopamine and sexual behavior

Among central neurotransmitters involved in the control of sexual behavior, dopamine is certainly one of the most extensively studied. Our attempt to review old and recent neuropharmacological, biochemical, electrophysiological, and psychobiological studies performed so far only in rats, monkeys, and humans, provides evidence that dopamine through its different neuronal systems and receptor subtypes plays different roles in the control of several aspects of sexual behavior. In fact, while the nigrostriatal system is necessary for the control of the sensory-motor coordination required for copulation, the mesolimbic-mesocortical system plays a key role in the preparatory phase of the behavior, mainly in sexual arousal, motivation and possibly reward. Conversely, the incertohypothalamic system plays a major role in the consummation of the behavior, mainly in seminal emission and erectile performance, but evidence for its involvement in sexual motivation also exists. The dopaminergic receptors playing the major role in the control of male sexual behavior belong to the D2 receptor subtype. However a D1/D2 receptor interaction is well established and an opposite role for D1 and D2 receptors in the preoptic area suggested. Despite some differences, most studies show that treatments that increase or decrease, respectively, brain dopaminergic activity improve or worsen, respectively, several parameters of copulatory activity, supporting a facilitatory role of dopamine in male sexual behavior. In contrast, no conclusion can be deduced from the available studies on the role of central dopaminergic systems in the control of proceptivity and receptivity, the two main components of female sexual behavior.

Effects of FG 5893, a new compound with 5-HT1A receptor agonistic and 5-HT2 receptor antagonistic properties, on male rat sexual behavior

In the present study male rat sexual behavior was used to explore the functional properties of FG 5893, a newly developed diphenylbutylpiperazinepyridyl derivative which is a 5-HT1A receptor agonist and a 5-HT2 receptor antagonist. Treatment with FG 5893 (0.1-6.0 mg kg-1) stimulated male rat sexual behavior, as evidenced by a decrease in the number of mounts and intromissions to elicit ejaculation, and a shortening of the ejaculation latency. The stimulatory effects varied in a dose-dependent manner, reaching a maximum at 3.0 mg kg-1. Pretreatment with (+/-)-pindolol (0.5 mg kg-1 -30 min), a selective 5-HT1A receptor antagonist, completely antagonized the stimulatory effects of FG 5893 (1 mg kg-1 -20 min) on male sexual behavior. In addition, the behavioral action of FG 5893 was investigated on various components of the 'serotonin behavior syndrome' including flat body posture, forepaw treading, and lower lip retraction. The effects obtained were compared with those induced by treatment with 8-hydroxy-2(di-n-propyl-amino)tetralin (8-OH-DPAT), the prototype of a 5-HT1A receptor agonist. Compared to 8-OH-DPAT, a 100 times higher dose of FG 5893 (10 mg kg-1) was needed to elicit flat body posture while forepaw treading was never seen. Lower lip retraction was elicited by the lowest doses of FG 5893 (0.1 mg kg-1) and 8-OH-DPAT (0.03 mg kg-1). Treatment with (+/-)-pindolol reduced flat body posture elicited by 8-OH-DPAT and completely eradicated the flat body posture induced by FG 5893.(ABSTRACT TRUNCATED AT 250 WORDS)

Stimulation of the hypothalamus initiates the urethrogenital reflex in male rats

The urethrogenital (UG) reflex is a spinal sexual reflex which is tonically inhibited in the intact male rat by neurons in the nucleus paragigantocellularis (nPGi). The medial preoptic area of the hypothalamus (MPOA) is involved in the activation of male sexual behavior. The present study examines the effect of hypothalamic stimulation on the UG reflex in the intact male rat. Areas of the hypothalamus were stimulated bilaterally with either electrical stimulation or D,L-homocysteic acid (DLH) and the presence of the UG reflex examined. Stimulation of discrete aras of the hypothalamus evoked the UG reflex. The UG reflex could be initiated in the absence of genital stimulation. Microinjections of DLH into the MPOA also initiate the UG reflex. These data suggest that stimulation of neurons in the MPOA overcome the inhibition by the nPGi and facilitate spinal genital reflexes leading to ejaculation.

5-HT1A and 5-HT1C/1D receptor agonists produce reciprocal effects on male sexual behavior of rhesus monkeys

Research has indicated that serotonin (5-HT) is involved in regulating male sexual behavior in rodent, as well as primate species. The present study was designed to further characterize 5-HT influences on male sexual behavior of rhesus monkeys. Experiment 1 examined the effects of 5-HT1A and 5-HT1C/1D receptor stimulation on penile erections and yawning behavior. Administration of the 5-HT1C/1D receptor agonist, m-chlorophenylpiperazine (m-CPP, 0.8 and 3.0 mg/kg), facilitated the occurrence of penile erection, and at doses greater than 0.2 mg/kg stimulated yawning. By contrast, the 5-HT1A receptor agonist, 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT, 0.01-0.2 mg/kg) did not significantly influence penile erections or yawning behavior. Experiment 2 evaluated the effects of m-CPP and 8-OH-DPAT on the behavior of male monkeys in the presence of a sexually receptive female monkey which the males could see, hear and smell, but not physically contact. Administration of m-CPP along with presentation of a receptive female stimulated penile erections to a greater extent than they were stimulated by either one of these manipulations alone. Administration of 8-OH-DPAT (0.1 and 0.2 mg/kg) produced a decrease in the percent of monkeys exhibiting penile erections in the presence of the female. In this experiment, yawning was affected in opposite directions, with m-CPP stimulating and 8-OH-DPAT decreasing the frequency of yawning. Experiment 3 assessed the effects of m-CPP on male copulatory behavior of rhesus monkeys. Administration of m-CPP (0.8-3.0 mg/kg) produced a dose-dependent decline in the percent of males initiating copulation and achieving ejaculation.(ABSTRACT TRUNCATED AT 250 WORDS)

Serotonergic influences on male sexual behavior of rhesus monkeys: effects of serotonin agonists

Although numerous studies in rats have demonstrated an influence of serotonin (5-HT) on male copulation, no studies have yet to demonstrate whether such a relationship exists in primate species. The present study sought to characterize 5-HT influences on male copulatory behavior of rhesus monkeys by using three different 5-HT agonists: a full 5-HT1A agonist, 8-hydroxy-2-(din-propylamino) tetralin (8-OH-DPAT); a partial 5-HT1A agonist, ipsapirone; and a 5-HT 1C/ID agonist, m-chlorophenylpiperazine (m-CPP). 8-OH-DPAT had a biphasic effect upon ejaculation latency, with low doses (5-10 micrograms/kg) producing a shortening of ejaculation latency (time from initiation of copulation to ejaculation), and the highest dose (100 micrograms/kg) producing a lengthening of ejaculation latency. Intromission frequency (number of intromissions preceding ejaculation) was affected only at 10 micrograms/kg 8-OH-DPAT with monkeys requiring fewer intromissions to ejaculation at this dose. Ipsapirone administration led to a shortening of ejaculation latency at all doses tested (50-800 micrograms/kg), and a reduction in intromission frequency at 200-800 micrograms/kg ipsapirone. Administration of the 5-HT 1C/1D agonist, m-CPP, resulted in an increase in ejaculation latency at 200-400 micrograms/kg m-CPP and mount latency at 400 micrograms/kg m-CPP, but did not affect intromission frequency. In summary, stimulation of 5-HT1A receptors lowered the ejaculatory threshold of the monkeys, while stimulation of 5-HT 1C/1D receptors interfered with copulatory behavior and raised the ejaculatory threshold.(ABSTRACT TRUNCATED AT 250 WORDS)

Copulation increases dopamine activity in the medial preoptic area of male rats

Dopamine (DA) metabolites in microdialysates from the medial preoptic area (MPOA) of male rats increased during copulation. These increases were not observed during eating of a highly palatable food, or if the animal failed to copulate, or if the microdialysis probe was anterior or dorsal to the MPOA. The only two animals with measurable serotonin (5-HT) levels while the female was present were also the only two that either failed to copulate or copulated but failed to ejaculate. These data are consistent with previous evidence for a facilitative role of MPOA DA in the control of male sexual behavior; however, 5-HT activity in the MPOA may impair copulation.

Further evidence showing that the inhibitory action of serotonin on rat masculine sexual behavior is mediated after the stimulation of 5-HT1B receptors

To explore whether the inhibitory actions of endogenous serotonin on rat male sexual behavior were mediated via the stimulation of the 5-hydroxytryptamine1A (5-HT1A) or 5-HT1B receptor subtypes, two series of studies were undertaken. In the first series, an attempt to block the inhibitory actions of threshold doses of the serotonin precursor 5-hydroxytryptophan (5-HTP, 50 mg/kg) by administering the beta-5-HT antagonist alprenolol (5.0 mg/kg) and the selective beta-blocker practolol (0.5 mg/kg) was made. Both antagonists effectively prevented, at least partially, the inhibitory actions of 5-HTP. In the second series, a possible synergistic effect of a subthreshold dose of 5-HTP (12.5 mg/kg) with low doses of the selective 5-HT1B agonist 1-(m-trifluoro-methylphenyl)piperazine (TFMPP,0.125 mg/kg) or the selective 5-HT1A agonist 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT, 0.0625 mg/kg) was investigated. A clear synergistic inhibitory effect of 5-HTP with TFMPP was observed. All data are interpreted based upon the hypothesis suggesting a physiological inhibitory role of the 5-HT1B receptor subtype on male rat sexual behavior.

A role for 5-hydroxytryptamine in descending inhibition of spinal sexual reflexes

Neurons in the region of the rostral nucleus paragigantocellularis (nPGi) mediate the inhibition of spinal sexual reflexes. Anatomical and pharmacological evidence is presented supporting a role for 5-hydroxytryptamine (5-HT) in this inhibition. Neurons in the rostral nPGi project to the ventral horn in the vicinity of the pudendal motoneurons. A significant number (78% ipsilateral) of these neurons contain 5-HT. Anterograde tracing with Phaseolus leucoagglutinin (PHA-L) confirmed the nPGi projection to pudendal motoneuron and interneuronal areas of the lumbar cord. 5-HT immunoreactive fibers and presumptive terminals surround the pudendal motoneurons. Urethral stimulation, in the anesthetized male rat, elicited penile erections, ejaculation and rhythmic contractions of the perineal muscles, we have used the term coitus reflex to describe this response. Intrathecal injection of 5-HT (4-50 micrograms) abolished the coitus reflex. Methysergide (1-10 mg/kg i.v.) prevented the 5-HT induced blockade of the coitus reflex. These data support the hypothesis that 5-HT is involved in the descending inhibition of spinal sexual reflexes.

Stimulation of 5-HT1A and 5-HT1B receptors in brain regions and its effects on male rat sexual behaviour

In the present series of experiments we compared the effect of injecting serotonin (40 micrograms/cannula), the 5-HT1A agonist, 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) (5.0 micrograms/cannula), and the 5-HT1B/C agonist, trifluoromethyl-phenyl-piperazine (TFMPP) (1.0 micrograms/cannula), into the preoptic area, the nucleus accumbens and the nucleus raphe dorsalis. The dose injected was selected on the basis of dose-response curves. Injection of serotonin and TFMPP into the medial preoptic area and nucleus accumbens resulted in an inhibition of male sexual behaviour, as evidenced by an increase in the number of mounts and a prolongation of the ejaculation latency. Injection of 8-OH-DPAT into these brain areas facilitated copulatory behaviour as evidenced by a reduction in the number of mounts, intromissions and ejaculation latency. Administration of these compounds into the nucleus raphe dorsalis produced no effect, except for a prolongation of the intromission latency after serotonin. These results would suggest that at least some of the 5-HT1A receptors involved in the facilitation of male sexual behaviour are located postsynaptically in limbic brain areas that regulate male sexual behaviour. On the basis of the similarities between the inhibitory effects of serotonin and TFMPP, the present results further support the idea that endogenous serotonin acts via the stimulation of 5-HT1B receptors to inhibit male sexual behaviour.

Effects of fenfluramine and para-chloroamphetamine on sexual behavior of male rats

The present studies have evaluated the effects of pharmacologically induced release serotonin on sexual responses of male rats during exposure to a sexually receptive female rat. Following acute administration of fenfluramine or para-chloroamphetamine (PCA), significant dose-related decreases in copulatory rate and copulatory efficiency, and increases in ejaculatory latency were observed. These effects were not observed when the animals were pretreated with LY53857, a 5-HT1c/2 antagonist. These studies indicate that acute release of serotonin evoked by these releasing agents has inhibitory effects on sexual sexual drive, capacity to achieve erection and threshold for ejaculation, and these effects are mediated by either the 5-HT1c or 5-HT2 receptor.

Sex behavior of male and female Wistar rats affected by the serotonin agonist 8-OH-DPAT

Four experiments were carried out to test the stimulatory effects of 8-OH-DPAT on various aspects of "masculine" sexual behavior of male and female rats and on the sexual attractivity of male rats. In Experiment 1 8-OH-DPAT (0.2 mg/kg) stimulated ejaculation frequency in middle-aged (approx. 15 months old) males, both sexually inactive and active subjects. There was a coinciding decrease in total number of mounts, intromissions, intromissions to first ejaculation and latency to first ejaculation. In Experiment 2 the effects of two doses (0.2 and 0.4 mg/kg) 8-OH-DPAT on the first ejaculation cycle were investigated. Especially, the higher dose made a high percentage (45-55%) of males to ejaculate "prematurely," i.e., at the first or second intromission. Latency to ejaculation decreased. With the higher dose, 25-35% of the males ejaculated extravaginally. In Experiment 3 8-OH-DPAT did not make males more attractive for an estrous female than saline-treated males, as judged by the time spent in their vicinity. However, estrous females received much more ejaculations from the tethered 8-OH-DPAT males, with the lowest latencies to first ejaculation, than from the saline-treated males. In Experiment 4 8-OH-DPAT stimulated mounting behavior in female rats only when they were long-term treated with testosterone. In that condition also shortest latencies to first mount were found with 8-OH-DPAT treatment.

Behavioral and biochemical effects of the 5-HT1A receptor agonists flesinoxan and 8-OH-DPAT in the rat

The 5-HT1A receptor agonists flesinoxan (0.2-3.2 mg kg-1 s.c.) and 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) (0.025-0.4 mg kg-1 s.c.) produced (1) a dose-dependent facilitation of male rat ejaculatory behavior and (2) characteristic, dose-dependent effects on spontaneous motor activity. Thus, total locomotor activity and rearing activity were decreased. However, forward locomotion and peripheral locomotion were increased relative to the total horizontal activity. Furthermore, (3) 5-HTP accumulation, after inhibition of cerebral decarboxylase, was dose dependently decreased by both compounds in the ventral striatum and in the prefrontal cortex. There was a statistically significant decrease in DOPA accumulation in the ventral striatum after administration of a high dose of flesinoxan (3.2 mg kg-1), and a tendency for 8-OH-DPAT to produce the same effect. The efficacy of the compounds to affect male rat sexual behavior, spontaneous motor activity in the open-field and forebrain 5-HT synthesis was approximately the same, whereas flesinoxan was about an order of magnitude less potent than 8-OH-DPAT.

DOI-induced inhibition of copulatory behavior in male rats: reversal by 5-HT2 antagonists

Relatively little is known regarding the role of 5-HT2 receptor activity in male rat sexual behavior. Previous work has yielded equivocal results, and both facilitation and inhibition of copulation have been reported to follow administration of selective 5-HT2 antagonists. In the present series of experiments, the ability of a variety of 5-HT2 antagonists to block inhibition induced by the 5-HT2/5-HT1C agonist DOI was examined. Systemic ritanserin, pirenperone and ketanserin all potently blocked DOI-induced (1.0 mg/kg SC) inhibition of mounts, intromissions and ejaculations. None of these drugs influenced the sexual behavior of the male rats when given alone in doses that effectively blocked DOI-induced inhibition. In addition, unlike ritanserin and ketanserin, pirenperone produced a biphasic effect on DOI-induced inhibition, exhibiting a diminished blockade at higher doses. This may be due to activity at receptors other than 5-HT2. Overall, the present data suggest that activity at 5-HT2 receptors mediates an inhibition of male rat sexual behavior.

Role of presynaptic serotonergic receptors on the mechanism of action of 5-HT1A and 5-HT1B agonists on masculine sexual behaviour: physiological and pharmacological implications

In order to establish whether the 5-HT1A or the 5HT1B agonists, 8-OH-DPAT or TFMPP, produce their facilitatory or inhibitory actions on masculine sexual behaviour via a mechanism involving: (a) the serotonin synthesis or release; (b) the stimulation of presynaptic receptors, or (c) the stimulation of somatodendritic receptors, three series of experiments were performed. The administration of the serotonin synthesis inhibitor, p-chlorophenylalanine (p-CPA, 300 mg/kg x 3 days), facilitated sexual behaviour but does not interfere neither with the inhibitory nor with the facilitatory effects of TFMPP (0.5 mg/kg) or 8-OH-DPAT (0.5 mg/kg), respectively. The icv or the intraraphé administration of the serotonergic neurotoxin, 5,7-dihydroxytryptamine (5,7-DHT), slightly stimulated masculine sexual behaviour and produced a decrease in serotonin and its metabolite levels. In lesioned animals TFMPP (0.5 mg/kg) resulted in an inhibitory effect reflected as a prolongation of the ejaculation latency. The inhibitory effect of this drug on mounting behaviour was not observed in 5,7-DHT treated rats. In lesioned animals 8-OH-DPAT (0.5 mg/kg) produced the same facilitatory effect. Present data indicate that serotonergic postsynaptic receptors mediate both the inhibitory and the facilitatory actions of TFMPP or 8-OH-DPAT in copulation. All data further support the idea that endogenous serotonin acts via the stimulation of 5-HT1B receptors to induce its inhibitory effects on masculine sexual behaviour.

Differential role of serotonin and noradrenaline on anxiety reduction after ejaculation in the rat

As previously reported, a reduction in anxiety after ejaculation was observed. In a previous report it was demonstrated that the GABA-benzodiazepine system is involved in the mediation of this reduction in anxiety. The anxiety levels were measured using a defensive burying model. This work was performed to elucidate the serotonin and noradrenaline participation in the mediation of this phenomenon. Two experiments were made. In the first experiment the serotonergic neurotoxin 5,7-dihydroxytryptamine (5,7-DHT, 10 micrograms/10 microliters) was intracerebroventricularly injected. Five days after its administration the behavioral tests were performed. In the second experiment, the noradrenergic neurotoxin N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP4, 50 mg/kg X 2) was IP administered. The neurochemical data reveal a drastic reduction in various brain areas respective monoamine levels after these treatments. The lesion produced by 5,7-DHT was able to reverse the reduction in anxiety in copulating males, but produced no changes in noncopulating animals. This finding supports the idea that the serotonergic system is involved in the reduction of anxiety observed after ejaculation. The results of the DSP4 experiment suggest that there is not a direct participation of the noradrenergic system in the anxiety reduction observed after ejaculation.

Opposite effects of 5-methoxy-N,N-di-methyl-tryptamine and 5-hydroxytryptophan on male rat sexual behavior

The administration of 5-methoxy-N,N-di-methyl-tryptamine (5-MeODMT), O-2.0 mg.kg-1 SC -15 min, produced a dose-dependent facilitation of the male rat sexual behavior, as evidenced by a decrease in the number of intromissions to ejaculation and in the ejaculation latency. The effects produced by 5-MeODMT (1 mg.kg-1) were antagonized by pindolol (4 mg.kg-1 SC -30 min), but not pirenperone (0.25 mg.kg-1 SC -30 min) or metergoline (1 mg.kg-1 SC -30 min), administration. As expected, 5-HTP (25 mg.kg-1 SC -60 min) produced an increased number of mounts and intromissions to ejaculation and an increase in the ejaculation latency in benserazide (25 mg.kg-1 SC -90 min) pretreated animals. Pindolol (4 mg.kg-1) by itself produced the same effects as seen after 5-HTP administration, and the combination of these compounds produced additive effects. Betaxolol (8 mg.kg-1 SC -30 min) had no effects of its own and did not interact with 5-HTP. The results suggest that stimulation of brain 5-HT1 or 5-HT2 receptors produces facilitation and inhibition, respectively, of the male rat sexual behavior.

Behavioural actions of the serotonergic anxiolytic indorenate

Several recent studies have shown that the 5-HT1A agonist indorenate possesses antianxiety properties. In the present study we report on other behavioural actions of this drug. Indorenate (31.6 mg/kg) induced flat body posture, forepaw treading and hind limb abduction, behavioural characteristics of the serotonin syndrome. After indorenate injection these same behaviours were observed in animals pretreated with p-chlorophenylalanine (400 mg/kg X 3 days), suggesting that the action of this compound is not mediated via serotonin release. The beta-5-HT1 blockers, (-) pindolol (2 mg/kg) or (-) alprenolol (5 mg/kg), did not prevent the actions of indorenate on the serotonin syndrome. Indorenate (10 mg/kg) stimulated the masculine sexual behaviour by reducing the number of intromissions preceding ejaculation. Higher doses (17.8 mg/kg) cause a complete inhibition of sexual behaviour. (-) Pindolol (2 mg/kg) or (-) alprenolol (5 mg/kg) did not antagonize the facilitatory actions of indorenate on male sexual behaviour. A high dose of indorenate (31.6 mg/kg) resulted in an impairment of the motor coordination as tested in a treadmill apparatus. These data reveal that indorenate possesses, in addition to its antianxiety effects, other behavioural characteristics that, however, appear at higher dose levels.