The spinal generator of ejaculation: Functional consequences of chronic spinalization and effect of substance P in anesthetized rats

What Is the Trigger for Sexual Climax?

A model is proposed to consider sexual climax in men, women, and animals as a unitary phenomenon. Sexual climax is a stereotyped rhythmic pattern of spinally generated neural activity in the autonomic and somatic nerves innervating pelvic organs. A column of neurons in the spinal cord of the male rat is strongly activated by ejaculation (sexual climax in the male). These neurons project to the thalamus and are therefore called lumbar spinothalamic cells (LSt cells). Comprehensive studies have demonstrated that the LSt cells constitute a central pattern generator of ejaculation. These findings have been extended to female animals. Further studies identified LSt cells in the lumbar spinal cord of men and women. Strong evidence indicates that the LSt cells mediate ejaculation in men. The climax model generalizes and extends these studies. It postulates that LSt cells in the lumbar spinal cord of humans and animals of both sexes generate climax. The LSt cells generate the neural activity driving the pelvic contractions and other responses of climax. The activity is transmitted to supraspinal sites to activate orgasm. The LSt cells receive excitatory and inhibitory projections from supraspinal sites. The descending projections reflect subjective arousal and inhibitions. Spinal sensory neurons from the genitals provide excitatory and inhibitory innervation to the LSt cells. These represent pleasurable and noxious sensations. The supraspinal and spinal excitatory and inhibitory inputs are integrated by the LSt. When the sum of the excitatory inputs, minus the sum of the inhibitory inputs reaches a threshold, the LSt cells generate sexual climax.

Lorcaserin Administration has Pro-Ejaculatory Effects in Rats via 5-HT2C Receptors Activation: A Putative Pharmacologic Strategy to Delayed Ejaculation?

BACKGROUND

Lorcaserin is an anti-obesity drug whose weight loss effect results from 5-hydroxytryptamin (5-HT)_2C receptors activation. The 5-HT_2C receptor was shown to participate in the physiological control of ejaculation, but no data addressing a putative effect of lorcaserin on ejaculation exist.

AIM

To investigate the effects of lorcaserin in different in vitro and in vivo experimental models of ejaculation in rats.

METHODS

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.

MAIN OUTCOME MEASURES

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.

RESULTS

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-HT_2C-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.

CLINICAL IMPLICATIONS

Due to its reported clinical safety, repurposing lorcaserin for the treatment of delayed ejaculation may be suggested.

STRENGTHS & LIMITATIONS

The pro-ejaculatory effect of lorcaserin administration and the role of 5-HT_2C 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.

CONCLUSION

Our results demonstrate that the clinically approved 5-HT_2C 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.

Central pattern generators in the brainstem and spinal cord: an overview of basic principles, similarities and differences

Central pattern generators (CPGs) are generally defined as networks of neurons capable of enabling the production of central commands, specifically controlling stereotyped, rhythmic motor behaviors. Several CPGs localized in brainstem and spinal cord areas have been shown to underlie the expression of complex behaviors such as deglutition, mastication, respiration, defecation, micturition, ejaculation, and locomotion. Their pivotal roles have clearly been demonstrated although their organization and cellular properties remain incompletely characterized. In recent years, insightful findings about CPGs have been made mainly because (1) several complementary animal models were developed; (2) these models enabled a wide variety of techniques to be used and, hence, a plethora of characteristics to be discovered; and (3) organizations, functions, and cell properties across all models and species studied thus far were generally found to be well-preserved phylogenetically. This article aims at providing an overview for non-experts of the most important findings made on CPGs in in vivo animal models, in vitro preparations from invertebrate and vertebrate species as well as in primates. Data about CPG functions, adaptation, organization, and cellular properties will be summarized with a special attention paid to the network for locomotion given its advanced level of characterization compared with some of the other CPGs. Similarities and differences between these networks will also be highlighted.

Neural Control and Physiology of Sexual Function: Effect of Spinal Cord Injury

Objective: To present the current understanding of normal anatomy, physiology, sexual physiology, pathophysiology and the consequential sexual changes and dysfunctions following a spinal cord injury (SCI). Methods: Narrative review of the latest literature. Results: Peripheral innervations of the pelvis involve 3 sets of efferent neurons coordinated though the pelvic plexus (somatic, thoracolumbar sympathetic, and sacral parasympathetic), and these are under cerebral descending excitatory and inhibitory control. SCI, depending on the level of lesion and completeness, can alter this cerebral control, affecting the psychological and reflexogenic potential for genital arousal and also ejaculation and orgasm. During arousal, nitric oxide is the main neurotransmitter for smooth muscle relaxation in both male and female erectile tissue. In men, erection, ejaculation, and orgasm are under separate neurological control and can be individually affected by SCI. Conclusions: Since sexual function is rated amongst the highest priorities by individuals living with SCI, methods employed to affect the neurological changes to maximize sexual neurophysiology prior to initiating medical therapies including paying attention to sexual sensate areas and visceral signals with mindfulness techniques, practicing body mapping, and sexual stimulation of sensate areas to encourage neuroplasticity. Attention should be paid to the biopsychosocial sexual contexts within which persons with SCI live to maximize their sexual and fertility rehabilitation.