Original articlesCharacterization of p-chloroamphetamine-induced penile erection and ejaculation in anesthetized rats
Abstract
Methodological shortcomings present in elicitation of male sexual reflexes in anesthetized animals. The present study has demonstrated, however, that intraperitoneal (i.p.) injection of p-chloroamphetamine (PCA), an indirect serotonin (5-HT) agonist, elicited simultaneously both penile erection and ejaculation in anesthetized rats. PCA (2.5–10.0 mg/kg, i.p.) caused an intermittent cluster of genital responses consisting of penile erection, glans erections, and penile cups, which closely resembles the response observed during the ex copula tests in unanesthetized rats. Measurements of intracavernous penile pressure showed that rhythmic changes in penile pressure were produced by PCA, together with glans erections and penile cups. PCA also caused a frequent ejaculations and the weighing of ejaculate accumulated over 0.5 hr was increased in a bell-shaped pattern, and the maximum effect was observed at 5.0 mg/kg. Pretreatment with p-chlorophenylalanine, a serotonin (5-HT) - synthesis inhibitor, significantly inhibited the expression of PCA-induced penile erection and ejaculation, while acute spinal transection at thoracic level did not affect the sexual responses. These results indicate that PCA-induced penile erection and ejaculation in anesthetized rats are mainly produced by the release of 5-HT, which is limited to the lower spinal cord and/or the peripheral sites. Furthermore, the sexual responses can be easily and reliably elicited by administration of PCA, which may be useful for the study of the mechanisms underlying male sexual functions.
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Central Mechanisms of Apomorphine and m-Chlorophenylpiperazine on Synergistic Action for Ejaculation in Rats
2021, Journal of Sexual MedicineWe 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-HT2C receptors, respectively.
The aim of this study was to clarify the target level of the proejaculatory effects induced by combination of these agonists.
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.
The presence and weight of ejaculatory plugs produced by drug-induced ejaculation and the contractile responses of the seminal vesicle were evaluated.
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-HT2C 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.
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-HT2C 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.
Lorcaserin Administration has Pro-Ejaculatory Effects in Rats via 5-HT<inf>2C</inf> Receptors Activation: A Putative Pharmacologic Strategy to Delayed Ejaculation?
2020, Journal of Sexual MedicineLorcaserin is an anti-obesity drug whose weight loss effect results from 5-hydroxytryptamin (5-HT)2C receptors activation. The 5-HT2C receptor was shown to participate in the physiological control of ejaculation, but no data addressing a putative effect of lorcaserin on ejaculation exist.
To investigate the effects of lorcaserin in different in vitro and in vivo experimental models of ejaculation in rats.
Contractile responses to lorcaserin in rat seminal emission organs in vitro (prostatic and epididymal vas deferens, cauda epididymis, and seminal vesicles), analysis of male rat copulatory behavior, and electromyographic recording of bulbospongiosus muscle in anesthetized animals were studied.
The main outcome measures included in vitro contraction of seminal emission organs and evaluation of the male rat copulatory behavior. The male rat sexual behavior in terms of copulation latency, ejaculation latency, mount and intromission frequency, and ejaculation frequency of sexually experienced adult male rats with a receptive female were also recorded.
Lorcaserin (1.0 nM to 1.0 mM) had no significant effects on the in vitro contractility of seminal emission organs smooth muscle (cauda epididymis, vas deferens, and seminal vesicles). On the other hand, lorcaserin administration (0.3–1.0 mg/kg, intravenous) induced ejaculation in anesthetized rats, which was prevented by the 5-HT2C-selective antagonist SB 242084 (0.1 and 0.3 mg/kg, intravenous). Single-dose treatment of non-anesthetized male rats with lorcaserin (1.0, 4.0, or 10 mg/kg, per os) induced non-copulating ejaculations in sexually naïve rats. Lorcaserin also had pro-ejaculation effects by decreasing the ejaculation threshold of copulating rats by half. The pro-ejaculatory effects of lorcaserin were reversible as the ejaculation threshold of treated rats recovered after a 1-week washout period.
Due to its reported clinical safety, repurposing lorcaserin for the treatment of delayed ejaculation may be suggested.
The pro-ejaculatory effect of lorcaserin administration and the role of 5-HT2C were demonstrated in different experimental models of ejaculation in rats. The lack of studies in putative experimental models of delayed ejaculation is a limitation of this study.
Our results demonstrate that the clinically approved 5-HT2C agonist lorcaserin is a strong facilitator of ejaculation in rats.
de Almeida Kiguti LR, Pacheco TL, Antunes E, et al. Lorcaserin Administration has Pro-Ejaculatory Effects in Rats via 5-HT2C Receptors Activation: A Putative Pharmacologic Strategy to Delayed Ejaculation? J Sex Med 2020;17:1060–1071.
Can Botulinum-A Toxin Be Used to Delay Ejaculation: Results of an Ejaculation Model in Male Rats
2019, Journal of Sexual MedicineCitation Excerpt :It is clear that these treatment options require the patients to engage in additional effort before each intercourse, which reduces the applicability and continuity of treatment. PCA is an indirect serotonin agonist, and the PCA-induced ejaculation model is an appropriate experimental rat model for investigating ejaculation physiology.12 In previous studies, the ejaculatory response following the administration of PCA usually begins in about the seventh minute.3,7,12
Although premature ejaculation (PE) is the most common sexual dysfunction in young men, its true pathophysiology has not yet been clearly elucidated.
To investigate the quantitative changes that occurred in an ejaculation model induced by para-chloroamphetamine (PCA) after botulinum-A toxin injection into the bulbospongiosus (BS) muscle in rats.
A total of 21 male rats weighing 300 to 350 grams were used in the study. The animals were divided into 3 groups: control, 1 unit of botulinum-A toxin injected, and 5 units of botulinum-A toxin injected. The botulinum-A toxin was percutaneously injected into the BS muscle, and the experiment was carried out 96 hours (5 days) after the injection.
The seminal vesicle (SV) was cannulated, and the BS muscle was dissected and connected to an amplifier (Biopac; Goleta, CA) to record the pressure and electromyography measurement. The ejaculation parameters were obtained after the PCA injection.
The ejaculation latency time of the group receiving 5 units of botulinum-A toxin was statistically significantly longer (1092 ± 657 seconds) compared to the control group (298 ± 81 seconds) and the group receiving 1 unit of botulinum-A toxin (439 ± 100 seconds) (P = .003). Furthermore, the BS EMG area under the curve values for the group receiving 5 units of botulinum-A toxin were significantly lower (7.4 ± 1.2 V/s × 10–4) than those of the control group (13.6 ± 4.0 V/s × 10–4) and the group receiving 1 unit of botulinum-A toxin (13.6 ± 5.0 V/s × 10–4) (P = .009). No statistically significant difference was found between the groups in terms of the basal SV pressure, number of SV phasic contractions, maximum amplitude of the SV phasic contraction, and intervals between the SV phasic contractions and the BS muscle contractions.
Botulinum-A toxin injection is a potential treatment option for PE and should be further investigated by future clinical studies.
Ease of administration and prolonged duration of botulinum-A toxin are advantages of the existing treatment options. The risk of anejaculation due to the dosage should be kept in mind.
Injection of botulinum-A toxin into the BS muscle in rats significantly delayed the ejaculation latency time and affected the expulsion phase.
Ongün S, Acar S, Koca P, et al. Can Botulinum-A Toxin Be Used to Delay Ejaculation: Results of an Ejaculation Model in Male Rats. J Sex Med 2019;16:1338–1343.
The neurologic control of arousal and orgasm with specific attention to spinal cord lesions: Integrating preclinical and clinical sciences
2018, Autonomic Neuroscience: Basic and ClinicalPreclinical research in animal models is important for understanding the neural pathways and pathophysiology underlying changes in sexual function after SCI. In vivo animal models, primarily rodents, have provided valuable information on the central pathways regulating sexual arousal and orgasm; however, further research is required in females and preclinical modeling of SCI that can be better translated to men and women. Translation of the autonomic and somatic regulation of sexual responses from preclinical models through clinical research correlates well with respect to the peripheral-spinal systems involved. However, due to the nature of sexual responses, parallel studies are necessary in animals and humans.
Human studies of individuals with SCIs have provided information about the neurologic control of arousal and orgasm. Psychogenic arousal is related to the preservation of sensation at T11-L2 whereas orgasm requires the presence of an intact sacral reflex arc. Studies point to evidence of a spinal pattern generator at L3-5. Because of the exact nature of SCIs, further research using neuroimaging will be beneficial, not only to elucidate the neurological control of sexual responses after SCI, but also in able-bodied individuals. Understanding and ameliorating the effects of SCI on sexual function is important to the well-being and quality of life of individuals with SCIs and their partners, thus future research should focus more on this important topic.
Unraveling the modulatory actions of serotonin on male rat sexual responses
2015, Neuroscience and Biobehavioral ReviewsAnimal studies and clinical investigations reveal that serotonin plays a central role in the control of the ejaculatory threshold. The chronic use of selective serotonin reuptake inhibitors (SSRIs) frequently results in sexual dysfunction, inviting to analyze the modulatory actions of serotonin on male sexual function in depth. Even though the main effect of serotonin on male sexual responses is inhibitory, this neuromodulator also mediates brief important stimulatory actions. Serotonin (5-HT) can activate two intracellular signaling pathways: a lower-threshold facilitatory pathway, and a higher-threshold inhibitory pathway, leading to biphasic effects. We propose that these divergent actions are related to the stimulation or inhibition of glutamatergic and GABAergic interneurons. Experimental evidence suggests that low 5-HT concentrations produce stimulatory actions on male ejaculatory aspects that might be mediated by the blockade of the GABAergic neurotransmission in the MPOA and spinal cord, which in turn releases a tonic inhibition that allows other neurotransmitters such as glutamate, noradrenaline, oxytocin and dopamine to initiate a sequence of molecular events resulting in the expression of ejaculation. Similar serotonin actions, mediated via interneurons, have been proposed for the regulation of other processes and occur in many central nervous system areas, indicating that it is not an isolated phenomenon.
Endothelins & erectile dysfunction
2011, Pharmacological ResearchCitation Excerpt :Penile erection is under both central and local neuromediation [5]. A large number of substances have been demonstrated experimentally to act at the supraspinal level; these include dopamine, oxytocin, adrenocorticotropic hormone, nitric oxide, serotonin, gamma-aminobutyric acid and cannabinoids [7–14]. Locally, a number of vasoactive mediators are released by the endothelial and smooth muscle cells of the CC.
Erectile dysfunction (ED) is common and a significant contributor to poor quality of life and psychosocial morbidity in men. Normal erectile function requires effective co-ordination between a number of complex neural pathways. Penile tumescence occurs in response to rapid arterial inflow to the corpora cavernosa with simultaneous venous outflow restriction due to expansion of the lacunar spaces. This process is under both central and local neuromediation.
Endothelins are potent vasoconstrictor peptides that cause strong, slowly developing but sustained contraction of trabecular smooth muscles cells of the corpora cavernosa. Multiple mechanisms of action are proposed, including transmembrane calcium flux, mobilisation of inositol triphosphate sensitive intracellular calcium stores and calcium sensitisation through the Rho-Rho kinase pathway.
The exact role of endothelins in the pathogenesis of ED currently remains unclear. Elevated endothelin-1 levels are found in patients with diabetes mellitus and this alone may be sufficient to cause ED. However, this is not borne out in clinical studies. The resultant elevated intracellular calcium may, however, modulate gene expression sufficiently to cause smooth muscle proliferation. Alternatively, alterations in endothelin receptor sensitivity in conditions such as diabetes and hypertension may enhance vasoconstrictor processes.
Currently there is contradictory evidence for the role of endothelin receptor antagonists in ED. Animals studies suggest they inhibit corporal vasoconstriction, improve erectile function and protect against diabetes-induced smooth muscle apoptosis. However, the results of clinical studies in ED have been less promising. Uncertainty regarding the exact role of endothelin in penile erection hampers progress in this area. It is possible that the endothelin system may only be relevant to ED in certain conditions where global endothelial dysfunction exists (e.g. diabetes mellitus, systemic sclerosis) and the use of endothelin antagonists in these patient groups may yield improved outcomes.