Bulbospongiosus Muscle Contractions Research Articles

Can Botulinum-A Toxin Be Used to Delay Ejaculation: Results of an Ejaculation Model in Male Rats

IntroductionAlthough premature ejaculation (PE) is the most common sexual dysfunction in young men, its true pathophysiology has not yet been clearly elucidated. AimTo 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. MethodsA 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. Main Outcome MeasureThe 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. ResultsThe 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. Clinical ImplicationsBotulinum-A toxin injection is a potential treatment option for PE and should be further investigated by future clinical studies. Strengths and LimitationsEase 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. ConclusionsInjection 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.

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

Oxytocin (OT) plays a major role in the control of male sexual responses. Notably, blockade of OT receptors has been reported to inhibit ejaculation in animals. The study aimed to investigate the action of a highly selective, non-peptide OT antagonist GSK557296 in a model of pharmacologically induced ejaculation in anaesthetized rats. The site of action was assessed by investigating different delivery routes for this compound. Urethane-anaesthetized Wistar rats were implanted with a cerebral ventricle cannula for i.c.v. injections or with a subdural catheter for intrathecal (i.t.) GSK557296 injections. Occurrence of ejaculation was assessed following i.v. 7-hydroxy-2-(di-N-propylamino)tetralin (7-OH-DPAT), a dopamine D3 receptor agonist. In addition, seminal vesicle pressures (SVP) and bulbospongiosus muscle (BS) EMG were recorded as physiological markers of emission and expulsion phases of ejaculation respectively. Highest i.v. GSK557296 dose reduced occurrence of ejaculation and increases in SVP but had no effect on BS-EMG. I.c.v. GSK557296 dose dependently inhibited ejaculation, increases in SVP and BS contractions. At spinal thoracic level, GSK557296 dose dependently inhibited ejaculation and increases in SVP but BS-EMG was impaired only with the highest dose. When delivered at lumbar level, GSK557296 dose dependently inhibited ejaculation, increases in SVP and BS contractions. In the 7-OH-DPAT-induced ejaculation model, GSK557296 acts peripherally and centrally to inhibit ejaculation with different modalities. Blockade of brain OT receptors seems to be the most effective mechanism of action. Targeting central OT receptors with highly selective antagonist seems a promising approach for the treatment of premature ejaculation.

Ejaculation Elicited by Microstimulation of Lumbar Spinothalamic Neurons

BackgroundNeuroanatomical and lesion studies have identified lumbar spinothalamic (LSt) neurons to be essential for ejaculation, but their precise role remains elusive. ObjectiveTo assess the role of LSt neurons as a spinal pattern generator for ejaculation (SGE) and their action on anatomical structures involved in the two ejaculation phases, the emission and expulsion of semen. DesignThe bulbospongiosus muscle (BSM) was implanted with electrodes and the seminal vesicle (SV) or vas deferens (VD) lumen catheterized in adult anaesthetized rats. Spinal exposure at the fourth lumbar segment (L4) allowed lowering an electrode stereotaxically into area VII/X for brief (300–500ms) electrical stimulation of LSt neurons, while recording BSM-EMG and intraluminal SV or VD pressure. ResultsBrief electrical microstimulation in the LSt neuron area evoked the expulsion of semen in 17 of 17 rats, with motile spermatozoa in 10 of 17 rats. After stimulation, SV/VD luminal pressure directly rose and fell, followed by rhythmic BSM contractions lasting ∼25s. Acute T8–T9 spinalization (n=4) did not alter the activation pattern of the BSM-EMG response. Injection of the GABAA-receptor agonist muscimol, inhibiting neuronal activity into the LSt neuron area after LSt neuron microstimulation (n=5), stopped BSM contractions in midstream. ConclusionsElectrical microstimulation of LSt neurons activates the entire sequence of ejaculation in rats in a coordinated fashion, ie the emission (SV/VD contraction) followed by expulsion (rhythmic BSM contractions) of living spermatozoa. Midcourse interruption of ejaculation following intraspinal muscimol injection establishes that LSt neurons are the SGE. This could help to identify spinal pharmacological targets for the treatment of ejaculatory disorders and provide the rationale for intraspinal stimulation to treat anejaculation in infertile spinal cord injured (SCI) patients.

Effect of Hyperforin-Enriched Extract on Pro-Ejaculatory Effect of 8-Hydroxy-2-(Di-N-Propylamino)Tetralin in Anesthetized Rats

Premature ejaculation is the most common male sexual dysfunction and, yet, no approved effective therapies are currently available. We studied the in vivo effectiveness of hyperforin (HF), a concentrated extract of Hypericum perforatum in an experimental model for the expulsion phase of ejaculation in anesthetized rats. The ejaculation model involved inducing rhythmic bulbospongiosus (BS) muscle contractions in male rats under urethane anesthesia (1.2 g/kg subcutaneously) by transiently raising the internal urethral pressure with saline infusion for 2 seconds at a rate of 116 microL/s. Electrodes in the BS muscles recorded the electrical activity during the contractions as a cluster of bursts on the electromyogram. Injection of the 5-hydroxytryptamine type 1A agonist 8-hydroxy-2-(di-N-propylamino)tetralin (8-OH-DPAT) (0.4 mg/kg subcutaneously) intensified the BS muscle contractions induced by increases in urethral pressure. Administration of 8-OH-DPAT strongly accelerated the ejaculation in the vehicle-treated rats and the amplitude of electrical discharges and the duration of electrical bursts accompanying the increases in urethral pressure were increased from baseline by 203.2% +/- 32.9% and 178.1% +/- 22.9%, respectively. The HF extract reduced the effects of 8-OH-DPAT on ejaculation at lower doses when tested in the dose range of 5 to 80 mg/kg. The reduction in the amplitude of bursts with HF extract remained unchanged after a midthoracic spinal transection, suggesting that the action of HF is either at the spinal ejaculation generator or directly on the neurons innervating the BS muscles. This is the first report of the effect of HF in a rat model of ejaculation. HF can be considered a novel new treatment of premature ejaculation.

Seminal Plug Expulsion Induced by Electrical Stimulation of the Intermesenteric Nerve in Anesthetized Rats

Synchronized activation of autonomic and somatic divisions of the nervous system respectively destined to the seminal tract, including the bladder neck and the pelvi-perineal striated musculature, is necessary for anterograde ejaculation. We aimed at investigating the role of intermesenteric nerves (IMNs) in ejaculation in anesthetized rats. Electrical stimulation of intact IMNs and distal and proximal stumps of the sectioned IMN were tested in isoflurane-anesthetized male rats. Electrical stimulation of the intact IMN was also applied to rats with acute spinal transection at the T8 level. The effects of IMN electrical stimulation on emission and expulsion phases of ejaculation were evaluated by measuring seminal vesicle pressure (SVP) and bulbospongiosus (BS) muscle contractions, respectively. IMN electrical stimulation could induce SVP increase and rhythmic contractions of BS muscle concomitantly with expulsion of the seminal plug. When compared with intact IMN electrical stimulation, the occurrence of ejaculation and rhythmic BS muscle contractions, but not SVP increase, was reduced in response to electrical stimulation of the distal stump of the sectioned IMN. In comparison to intact IMN electrical stimulation, the occurrence of ejaculation and rhythmic BS muscle contractions was not significantly modified, whereas the increase in SVP was diminished when the proximal stump of the sectioned IMN was stimulated. Spinalization abolished ejaculation and rhythmic BS muscle contraction but did not impair SVP increase. It is concluded that both afferents conveyed by IMN and relaying supraspinally and efferents of IMN are involved in IMN electrical stimulation-induced ejaculation. We propose that the IMN electrical stimulation paradigm can be used to investigate physiological and pharmacologic aspects of ejaculation.

Ejaculation induced by i.c.v. injection of the preferential dopamine D 3 receptor agonist 7-hydroxy-2-(di-N-propylamino)tetralin in anesthetized rats

In addition to serotonin, dopamine within the CNS is known to play a primary role in the control of ejaculation. However, whether D 2 and/or D 3 dopamine receptor subtypes mediate this effect is still unclear. In order to clarify this issue, a pharmacological competitive study using the preferential D 3 agonist 7-hydroxy-2-(di-N-propylamino)tetralin (7-OH-DPAT) alone or in combination with competitive nonpreferential or preferential D 2 and D 3 antagonists delivered intracerebroventricularly (i.c.v.) was undertaken in anesthetized rats. Urethane-anesthetized male rats were implanted into the cerebral ventricle with a cannula for i.c.v. injections, and recording electrodes were placed within the bulbospongiosus (BS) muscle to monitor BS muscle contractions, which were used as a marker for the expulsion phase of ejaculation. Following i.c.v. injection, 7-OH-DPAT induced ejaculation and rhythmic BS muscle contractions. Co-injected i.c.v. with 7-OH-DPAT, the nonselective D 2/D 3 antagonist (raclopride), and the preferential D 3 antagonist (S(−)-N[n-butyl-2-pyrrolidinyl)methyl]-1-methoxy-4-cyanonaphtalene-2-carboxamide; nafadotride) but not the preferential D 2 antagonist ((±)-3-[4-(4-chlorophenyl)-4-hydroxypiperidinyl]methylindole; L 741,626) inhibited the occurrence of ejaculation and BS muscle contractions. These results suggest that i.c.v. delivery of 7-OH-DPAT does represent a pertinent model to investigate the physio-pharmacology of ejaculation. It is inferred that targeting brain D 3 receptors may provide a therapeutic approach for treating ejaculatory disorders in humans.

Comparison between tamsulosin and alfuzosin on the expulsion phase of ejaculation in rats

To investigate the effects of acute intravenous (i.v.) delivery of tamsulosin and alfuzosin on the contractions of bulbospongiosus muscles (BS) induced by central delivery of a serotonin agonist, 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), in anaesthetized rats, as an experimental model of the expulsion phase of ejaculation. Under urethane anaesthesia, adult male rats were implanted with a cannula into the lateral cerebral ventricle for intracerebroventricular (i.c.v.) injection, and with recording electrodes in the BS for electromyogram (EMG) monitoring. Tamsulosin (1 microg/kg) and alfusozin (10 microg/kg) were injected i.v. and 15 min later 8-OH-DPAT (20 microg) was delivered i.c.v. BS-EMG recording was continued for 30 min after i.c.v. 8-OH-DPAT. The area under the curve (AUC) of the BS cluster of contractions was determined as reflecting the energy of BS contractions. After i.c.v. delivery of 8-OH-DPAT, there were rhythmic BS contractions in the form of clusters of bursts in vehicle-, tamsulosin- and alfuzosin-treated rats. The number of BS clusters was not altered by the alpha1-blockers as compared with vehicle, but the AUC was significantly less in tamsulosin-treated rats than in vehicle- or alfuzosin-treated (both P < 0.05) rats. Systemic injection of tamsulosin impaired BS contractile capacity whereas alfuzosin did not. This might explain anejaculation in men treated with tamsulosin.

Role of Peripheral Innervation in P‐Chloroamphetamine—Induced Ejaculation in Anesthetized Rats

The occurrence of ejaculation, which consists of 2 distinct phases (emission and expulsion), requires a tight coordination of peripheral autonomic and somatic nerves. However, some aspects of the mechanism of ejaculation are not clearly defined. To clarify this issue, we used the p-chloroamphetamine (PCA)-induced ejaculation model in anesthetized rats and investigated the effects of selective peripheral nerves lesions on seminal vesicle and bulbospongiosus (BS) muscle activities as representing physiological markers of emission and expulsion phases, respectively. In intact rats, ejaculation induced with PCA (intraperitoneal 5 mg/kg) correlated with coordinated increases in seminal vesicle pressure (SVP) and BS electromyographic activity. PCA-induced ejaculation was still observed in rats with bilateral lesion of hypogastric nerves (HNx), lumbar paravertebral sympathetic chain (LSCx), or dorsal nerves of the penis (DNPx). Conversely, bilateral section of pelvic nerves (PNx) or L6-S1 dorsal roots (DRx) abolished PCA-induced ejaculation. The amplitude of SVP increases induced by PCA was reduced in PNx, HNx, and LSCx rats, whereas it was unchanged in DRx and DNPx rats. The time interval between SVP increases and BS muscle contractions induced by PCA was comparable in the different neural lesion groups. In conclusion, PCA initiates both emission and expulsion independently from each other. In this model, afferents conveyed by the pelvic nerves appear to be unnecessary for occurrence of BS muscle contractions but are essential for a complete ejaculatory response.

D2-Like Receptors Mediate the Expulsion Phase of Ejaculation Elicited by 8-Hydroxy-2-(di-N-propylamino)tetralin in Rats

The mechanism of action by which 8-hydroxy-2-(di-N-propylamino)tetralin (8-OH-DPAT) facilitates ejaculation in conscious rats is not clearly established. The serotonin (5-HT) 1A agonist 8-OH-DPAT may actually act on cerebral dopaminergic receptors to exert its proejaculatory effect. The present work was undertaken to clarify this issue by testing various compounds i.c.v. delivered in an experimental model of the expulsion phase of ejaculation in anesthetized Wistar rats. Intracerebroventricular delivery of 8-OH-DPAT dose-dependently (ED(50) = 17 microg) induced rhythmic contractions of bulbospongiosus (BS) muscles, which are of paramount importance for the expulsion of semen, occurring in the form of cluster of bursts evidenced by the recording of BS muscle electrical activity. The 5-HT1A antagonist WAY100635 (N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-2-pyridinylcyclohexanecarboxamide) (20 microg) i.c.v. coadministered with 8-OH-DPAT (20 microg) was unable to inhibit the effect of 8-OH-DPAT on BS muscle contractile activity. Conversely, raclopride (40 microg) and spiperone (10 microg), both dopamine D2-like receptor antagonists, i.c.v. coinjected with 8-OH-DPAT (20 microg), abolished BS muscle contractions. The involvement of D2-like receptors was further supported by the fact that the D2-like agonist quinelorane (20 microg i.c.v.) also induced BS muscle rhythmic contractions. Our data demonstrate that D2-like receptors mediate the induction by 8-OH-DPAT of rhythmic BS muscle contractions and suggest that i.c.v. delivery of D2-like receptor agonists to anesthetized rats represents a relevant experimental model to study the expulsion phase of ejaculation.

3H-spiperone binds with high affinity to a non-dopaminergic site on human B-lymphocytes, EBV transformed lymphoblasts and macrophages

In addition to serotonin, dopamine within the CNS is known to play a primary role in the control of ejaculation. However, whether D2 and/or D3 dopamine receptor subtypes mediate this effect is still unclear. In order to clarify this issue, a pharmacological competitive study using the preferential D3 agonist 7-hydroxy-2-(di-N-propylamino)tetralin (7-OH-DPAT) alone or in combination with competitive nonpreferential or preferential D2 and D3 antagonists delivered intracerebroventricularly (i.c.v.) was undertaken in anesthetized rats. Urethane-anesthetized male rats were implanted into the cerebral ventricle with a cannula for i.c.v. injections, and recording electrodes were placed within the bulbospongiosus (BS) muscle to monitor BS muscle contractions, which were used as a marker for the expulsion phase of ejaculation. Following i.c.v. injection, 7-OH-DPAT induced ejaculation and rhythmic BS muscle contractions. Co-injected i.c.v. with 7-OH-DPAT, the nonselective D2/D3 antagonist (raclopride), and the preferential D3 antagonist (S(−)-N[n-butyl-2-pyrrolidinyl)methyl]-1-methoxy-4-cyanonaphtalene-2-carboxamide; nafadotride) but not the preferential D2 antagonist ((±)-3-[4-(4-chlorophenyl)-4-hydroxypiperidinyl]methylindole; L 741,626) inhibited the occurrence of ejaculation and BS muscle contractions. These results suggest that i.c.v. delivery of 7-OH-DPAT does represent a pertinent model to investigate the physio-pharmacology of ejaculation. It is inferred that targeting brain D3 receptors may provide a therapeutic approach for treating ejaculatory disorders in humans.