Muscarinic and nicotinic influences on masculine sexual behavior in rats: effects of oxotremorine, scopolamine, and nicotine

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.

Role of acetylcholine in control of sexual behavior of male and female mammals

The results of studies using systemic or central applications of cholinergic drugs suggest that acetylcholine makes important contributions to the neurochemical control of male- and female-typical reproductive behaviors. In males, cholinergic control seems largely specific to some elements or aspects of copulatory behavior that can vary significantly across species. Synapses in or near the medial preoptic area represent part of this mechanism, but the entire system appears to extend more widely, perhaps especially to one or more structures flanking some part of the lateral ventricle. In females, the lordosis response that essentially defines sexual receptivity is clearly responsive to cholinergic drugs. The same seems likely to be true of other elements of female sexual behavior, but additional studies will be needed to confirm this. Changes in cholinergic activity may help to mediate estrogenic effects on female sexual behavior. However, estrogen exposure can increase or decrease cholinergic effects, suggesting a relationship that is complex and requires further analysis. Also presently unclear is the localization of the cholinergic effects on female sexual responses. Though periventricular sites again have been implicated, their identity is presently unknown. This review discusses these and other aspects of the central cholinergic systems affecting male and female sexual behaviors.

Potential contribution of aromatase inhibition to the effects of nicotine and related compounds on the brain

Cigarette smoking continues to be a major public health problem, and while smoking rates in men have shown some decrease over the last few decades, smoking rates among girls and young women are increasing. Practically all of the important aspects of cigarette smoking and many effects of nicotine are sexually dimorphic (reviewed by Pogun and Yararbas, 2009). Women become addicted more easily than men, while finding it harder to quit. Nicotine replacement appears to be less effective in women. This may be linked to the observation that women are more sensitive than men to non-nicotine cues or ingredients in cigarettes. The reasons for these sex differences are mostly unknown. Several lines of evidence suggest that many of the reported sex differences related to cigarette smoking may stem from the inhibitory effects of nicotine and other tobacco alkaloids on estrogen synthesis via the enzyme aromatase (cyp19a gene product). Aromatase is the last enzyme in estrogen biosynthesis, catalyzing the conversion of androgens to estrogens. This review provides a summary of experimental evidence supporting brain aromatase as a potential mediator and/or modulator of nicotine actions in the brain, contributing to sex differences in smoking behavior. Additional research on the interaction between tobacco smoke, nicotine, and aromatase may help devise new, sex specific methods for prevention and treatment of smoking addiction.

Cholinergic control of male mating behavior in hamsters: effects of central oxotremorine treatment

The responses of rats to intracranial injections of cholinergic drugs implicate acetylcholine in the control of male mating behavior and suggest specific brain areas as mediators of these effects. In particular, past work has linked the medial preoptic area (MPOA) to the control of intromission frequency but implicated areas near the lateral ventricles in effects on the initiation and spacing of intromissions. Studies of responses to systemic cholinergic treatments suggest that acetylcholine is even more important for the control of mating behavior in male hamsters but provide no information on the relevant brain areas. To fill this gap, we observed the effects of central injections of the cholinergic agonist oxotremorine that approached the MPOA along contrasting paths. Both studies suggest that increased cholinergic activity in or near the MPOA can facilitate behavior by reducing the postejaculatory interval and possibly affecting other parts of the mechanisms controlling the initiation of copulation and the efficiency of performance early in an encounter. In addition, oxotremorine caused other changes in behavior that could not be tied to the MPOA and may reflect actions at more dorsal sites, possibly including the bed nucleus of the stria terminalis and medial septum. These effects were notably heterogeneous, including facilitatory and disruptive effects on male behavior along with a facilitation of lordosis responses to manual stimulation. These results emphasize the number and diversity of elements of sexual behavior in hamsters that are under the partial control of forebrain cholinergic mechanisms.

Cholinergic control of male mating behavior in hamsters: effects of systemic agonist or antagonist treatment

Sexual behavior in male rats is thought to depend in part on central cholinergic activity. In particular, previous studies of responses to systemically administered cholinergic drugs suggest that male rat behavior can be facilitated by the muscarinic agonist oxotremorine but is disrupted by the muscarinic antagonist scopolamine. However, it is not clear how broadly these effects generalize across species. To address this issue, we observed the impact on sexual behavior in male hamsters of systemic treatment with oxotremorine or scopolamine. In each case, the peripheral muscarinic antagonist methylscopolamine was used as an auxiliary or control treatment to better isolate central cholinergic effects. Both oxotremorine and scopolamine disrupted male behavior in hamsters. For example, both increased the likelihood of failure to achieve intromission or ejaculation. Further, even on completed tests oxotremorine treatment led to changes including increases in mount latency and postejaculatory interval while scopolamine treatment caused changes including increases in ejaculation latency and intromission frequency. The many changes caused by these treatments suggest that acetylcholine helps to control many elements of male behavior, probably by acting at multiple brain sites. The generally similar responses to a cholinergic agonist and antagonist suggest the dependence of efficient mating behavior on optimal levels of central cholinergic activity.

Vitamin E modulates reproductive toxicity of pyrethroid lambda-cyhalothrin in male rabbits

The objective of the current study was to analyze the reproductive toxicity caused by lambda-cyhalothrin (LCT) in male rabbits, and to evaluate the possible protective effect of vitamin E (Vit. E) as antioxidant. Animals were orally administered their respective doses of LCT every other day and given drinking water supplemented with vitamin E for 16 weeks. Results showed that semen quality was deteriorated following treatment with LCT. Also, testosterone levels, body weight (BW), feed intake (FI), and relative testes (RTW) and epididymis (REW) weights were significantly decreased. Concentrations of thiobarbituric acid-reactive substances (TBARS) were significantly increased in seminal plasma of rabbits treated with LCT compared with control. While, activities of glutathione S-transferase (GST), transaminases and acid phosphatase (AcP) were significantly decreased. Vitamin E alone significantly increased testosterone levels, BW, FI, RTW, REW, semen characteristics and seminal plasma enzymes, and decreased the levels of TBARS. Also, the present study showed that vitamin E might be effective against LCT-induced reproductive toxicity. It was suggested that LCT exerted a significant adverse effect on reproductive performance of male rabbits. Furthermore, vitamin E antagonized the toxic effects of LCT and improved semen quality of male rabbit.

Muscarinic receptor antagonism at the spinal cord level causes inhibitory effects on male rat sexual behavior

The role of cholinergic neurotransmission in male rat sexual behavior at the brain level has been studied by several researchers. However, little is known about its role at the spinal cord level. In this study, the effects of the intrathecal (IT) administration of the muscarinic receptor antagonist subtypes (MRAs) methoctramine (Meth), tropicamide (Trop) and 4-DAMP on male rat sexual behavior were evaluated during three ejaculatory series. Meth and Trop are preferring antagonists for the M2/M4 receptor subtypes, and 4-DAMP is a preferring antagonist for the M3 receptor subtype. All the MRAs tested noticeably inhibited male rat copulatory behavior, reflected by a reduction in the number of animals engaging in sexual behavior and a gradual decrease in the number of animals able to ejaculate. Significant increases in intromission latency (IL), ejaculation latency (EL) and post-ejaculatory interval (PEI) were observed. The ranking of inhibitory potency in all recorded parameters was Meth>/=4-DAMP>Trop. In theory, the effects of Meth and Trop could be a result of interaction with M2/M4 receptors. However, given that the M2 receptor constitutes the greatest population of muscarinic receptors at all spinal cord sites and given the high affinity for Meth on M2 receptors, the high potency in the inhibitory effects of Meth is indicative of the special role of M2 spinal receptors in the implementation of this behavior. The weaker effects of Trop could be linked to the smaller population of M4 receptors in the spinal cord, but some interaction with M2 receptors is probable. Since some differences in the pattern of inhibitory response between Meth and 4-DAMP were observed in this and a previous study, a possible role for M3 receptors must be considered. The data obtained in this study confirm the facilitating effect of acetylcholine (ACh) at the spinal cord level on male rat sexual behavior through muscarinic mechanisms, with an important influence on ejaculatory processes. These data support the hypothesis of the modulating role of ACh on male rat sexual behavior at the spinal cord level.

Sexual function in adult male rats after prenatal modulation of the cholinergic system

Prenatal administration of the n-cholinolytic ganglerone to pregnant female rats at different periods of gestation was found to lead to long-term changes in sexual behavior in pubescent offspring: there was a reduced dynamic of acquiring sexual experience and a very low level of sexual activity, with significant impairment to the motivational and ejaculatory components of sexual behavior. The number of males with reduced sexual activity in the experimental groups was significantly greater than that in control offspring. The results obtained here provide evidence that impairments of sexual function in adult offspring induced by prenatal administration of the n-cholinolytic ganglerone at 9-11 and 12-14 days of gestation and, to a lesser extent, the m-cholinolytic metamyzil at 9-11 days of gestation, were due to impairment to the central mechanisms regulating sexual function due to stable changes in neurotransmitter activity in the hippocampus and hypothalamus, along with a significant reduction in the blood testosterone level.

Masculine sexual behavior features in the Flinders sensitive and resistant line rats

The Flinders sensitive (FSL) and resistant (FRL) lines of rats have been selectively bred for their differences in cholinergic sensitivity. The FSL rats display hypersensitive responses to agonists of muscarinic receptors. In addition, the FSL rats display behavioral alterations that support the notion that this strain could be useful as an animal model of depression. These abnormalities include increase in rapid eye movement sleep, decrease of saccharin consumption after stress, and reduced exploratory behavior in a novel open field. On the other hand, sexual behavior is a pleasure-seeking behavior that should be altered in a mood disorder characterized by anhedonia. In the present study, spontaneous masculine sexual behavior features were analyzed, both during 30-min tests as well as during a satiety test. Results showed that, compared to outbred Sprague-Dawley (SD) rats, both the FSL and the FRL rats displayed some behavioral impairment, like a marked decrease of the ejaculatory frequency. During the satiety tests, both the FSL and the FRL rats became exhausted sooner than their SD controls. In addition to considering the present results in terms of alterations in specific neurotransmitter systems, endogamy is proposed as a possible source of the behavioral alterations.

Pharmacological features of masculine sexual behavior in an animal model of depression

Neonatal treatment with clomipramine induces behavioral alterations during adulthood that resemble symptoms observed in human depression. Therefore, it has been proposed as an animal model of depression. Impairment of male sexual performance is one of the main effects of this treatment. Using this model of depression, we evaluated the effects of drugs that stimulate sexual performance by acting selectively on the adrenergic, serotonergic, or cholinergic system. Yohimbine, a selective antagonist of the alpha-2 receptors; 8-OH-DPAT, a selective agonist of the 5-HT1A receptors; and oxotremorine, a muscarinic agonist, were administered to male rats neonatally treated with clomipramine that showed sexual behavior impairments. Yohimbine and oxotremorine induced only a slight improvement of sexual deficiencies. 8-OH-DPAT not only restored sexual behavior to normal levels, but induced facilitation in most of the copulatory parameters. These results suggest that neonatal treatment with clomipramine induces sexual deficits acting mainly on the adrenergic and cholinergic systems, while the serotoninergic system seems to be preserved.

Cholinergic-androgenic interaction in the regulation of male sexual behavior in rats

It is well known that testosterone (T) plays a major role in the adequate expression of male sexual behavior. On the other hand, the stimulation of central muscarinic receptors with oxotremorine (OXO), a specific agonist, facilitates the expression of masculine sexual behavior in rats. In this study, we analyzed the relationship between T and the cholinergic system, recording the effect of OXO administration on masculine sexual behavior in gonadectomized rats, before and after receiving T treatment. Sexually experienced and unexperienced male rats were gonadectomized and periodically tested for sexual behavior. Once this behavior was absent or drastically reduced, males were treated with OXO or saline and sexual behavior was assessed. 112 or 167 days later, animals were treated daily with T during 21 days, recording the response to OXO in days 12 and 21. Sexual behavior decreased more rapidly after gonadectomy in inexperienced males. OXO administration did not improve sexual performance in either group. The administration of T rapidly restored sexual behavior of experienced males: recovery of inexperienced males was slower. In the presence of T, OXO administration exerted a facilitative effect on sexual performance of both groups. These results suggest that the facilitative effect of muscarinic stimulation on sexual behavior requires the presence of testosterone.

Antidepressant-induced orgasm disorder

Most of the antidepressants approved for use in the United States, with the possible exceptions of bupropion and nefazodone, have been associated with drug-induced anorgasmia. Common strategies to overcome this drug side effect include waiting for tolerance to develop, dose reduction, change of dosing regimen, substitution of an alternative antidepressant, and coadministration of another drug. Current evidence suggests that antidepressant-induced anorgasmia may be mediated by 5HT2 antagonism of adrenergic mechanisms that underlie normal orgasm.