Stress affects a gastrin-releasing peptide system in the spinal cord that mediates sexual function: implications for psychogenic erectile dysfunction

Neuropeptidergic control circuits in the spinal cord for male sexual behaviour: Oxytocin-gastrin-releasing peptide systems

The neuropeptidergic mechanisms controlling socio-sexual behaviours consist of complex neuronal circuitry systems in widely distributed areas of the brain and spinal cord. At the organismal level, it is now becoming clear that "hormonal regulations" play an important role, in addition to the activation of neuronal circuits. The gastrin-releasing peptide (GRP) system in the lumbosacral spinal cord is an important component of the neural circuits that control penile reflexes in rats, circuits that are commonly referred to as the "spinal ejaculation generator (SEG)." Oxytocin, long known as a neurohypophyseal hormone, is now known to be involved in the regulation of socio-sexual behaviors in mammals, ranging from social bonding to empathy. However, the functional interaction between the SEG neurons and the hypothalamo-spinal oxytocin system remains unclear. Oxytocin is known to be synthesised mainly in hypothalamic neurons and released from the posterior pituitary into the circulation. Oxytocin is also released from the dendrites of the neurons into the hypothalamus where they have important roles in social behaviours via non-synaptic volume transmission. Because the most familiar functions of oxytocin are to regulate female reproductive functions including parturition, milk ejection, and maternal behaviour, oxytocin is often thought of as a "feminine" hormone. However, there is evidence that a group of parvocellular oxytocin neurons project to the lower spinal cord and control male sexual function in rats. In this report, we review the functional interaction between the SEG neurons and the hypothalamo-spinal oxytocin system and effects of these neuropeptides on male sexual behaviour. Furthermore, we discuss the finding of a recently identified, localised "volume transmission" role of oxytocin in the spinal cord. Findings from our studies suggest that the newly discovered "oxytocin-mediated spinal control of male sexual function" may be useful in the treatment of erectile and ejaculatory dysfunction.

Sexual Dysfunction in Patients With Chronic Gastrointestinal and Liver Diseases: A neglected Issue

INTRODUCTION

Normal sexual activity is an important determinant of quality of life. Unfortunately, several chronic health disorders are associated with an impaired sexual function.

OBJECTIVE

To provide coverage of the current literature on prevalence and pathophysiology of sexual dysfunction in patients with gastrointestinal and liver disorders METHODS: A Comprehensive review of the literature on the prevalence of sexual dysfunction in chronic gastrointestinal and liver disorders, assessing the underlying mechanism (s) was performed.

RESULTS

Many gastrointestinal disorders, either functional or organic, are associated with some degree of sexual dysfunction. The main pathogenic mechanisms are: (i) the disease itself causing fatigue, anxiety or depression with a potential alteration of self-esteem; (ii) worry of transmitting a potential infectious agent through sexual activity; (iii) alteration of the endocrine mechanisms which are necessary for normal sexual functioning; (iv) chronic pro- inflammatory conditions which may cause endothelial dysfunction and abnormal vascular responses; (v) iatrogenic.

CONCLUSION

Based on this review, a thorough evaluation of sexual function through validated questionnaires and/or psychological interviews with patients with chronic gastrointestinal disorders should be part of the clinical assessment in order to timely diagnose and possibly treat sexual dysfunction in this clinical setting. L Romano, L Granata, F Fusco, et al. Sexual Dysfunction in Patients With Chronic Gastrointestinal and Liver Diseases: A neglected Issue. Sex Med Rev 2021;XX:XXX-XXX.

Evaluation of the effects of chronic stress applied from the prepubertal to the adult stages or only during adulthood on penile morphology in rats

The present study aimed to evaluate the effects of chronic stress from the prepubertal to the adult stages or during adulthood on penile morphology in rats. The animals were immobilized in a cylinder for 2 h daily for a total of six weeks to simulate stress. Ten rats were exposed to stress stimulus beginning from the prepubertal age, while nine rats were exposed to stress stimulus only during adulthood. Animals were killed at 24 h after the last stress session for short-term evaluation (SP-S and SA-S), while other age-matched rats were sacrificed at 6 weeks after the last stress session for long-term evaluation (SP-L and SA-L). Age-matched animals were used as controls (CP-S, CA-S, CP-L and CA-L). After treatment, serum testosterone levels and areas of cavernosum structures were evaluated. We observed no changes in serum testosterone levels after stress treatment. Results revealed that the area of the corpus cavernosum without the tunica albuginea in animals in the SA-S group was 16% lower than that in the CA-S group. The smooth muscle was 31% lower in the SP-L group than in the SP-S group and 42% lower in the SA-S group than in the CA-S group. The elastic fiber system was 48% lower in the SP-L group than in the CP-L group and 59% lower in the SA-S group than in the CA-S group. Chronic stress promoted morphological changes in the rat penis and was significantly more pronounced when the stress occurred throughout the adulthood. Chronically applied single stress stimulus caused greater damage to the penis when induced directly during adulthood than when introduced before puberty to adulthood and could be associated with erectile dysfunction.

The Role of Nocturnal Penile Tumescence and Rigidity (NPTR) Monitoring in the Diagnosis of Psychogenic Erectile Dysfunction: A Review

INTRODUCTION

Nocturnal penile tumescence and rigidity (NPTR) monitoring with RigiScan was considered one of the most reliable methods to differentiate psychogenic erectile dysfunction (pED) from organic ED. However, its reliability has been questioned because of some limitations in the practice.

AIM

To present contemporary views on the role of NPTR monitoring in the diagnosis of pED.

METHOD

We performed a comprehensive review of English-language literature on NPTR and pED by a PubMed search.

MAIN OUTCOME MEASURES

Studies were included if the mechanisms of pED and nocturnal erection and the practice of NPTR monitoring in ED were the main research contents.

RESULTS

The pED results from not only psychosocial factors but also physiological changes containing central nervous abnormality. NPTR monitoring with RigiScan is still considered a useful method for the diagnosis of pED. A normal NPTR recording in a man with ED complaints probably suggests pED, whereas an abnormal recording may represent organic ED. Radial rigidity of no more than 60% is correlated well with axial rigidity, but, when it is more than 60%, the correlation between them is questioned. The consistency between NPTR and sex-stimulated erection is questionable, and the correlation of NPTR with different patient-reported outcome scoring systems is different. A normal NPTR recording in patients with ED does not necessarily mean pED, especially in patients with spinal cord injury. NPTR recordings can be influenced by depression, smoking, aging, negative dream content, and sleep disorders.

CONCLUSION

NPTR monitoring with the RigiScan is still considered a useful diagnostic tool for pED at the present stage. However, there are some disputes regarding the correlation between penile radial rigidity and axial rigidity and between NPTR and sex-related erection, as well as normative evaluation criteria for ED and the possibility of a false NPTR result, that need to be further studied. Zou Z, Lin H, Zhang Y, et al. The Role of Nocturnal Penile Tumescence and Rigidity (NPTR) Monitoring in the Diagnosis of Psychogenic Erectile Dysfunction: A Review. Sex Med Rev 2019;7:442-454.

Brain atrophy in the visual cortex and thalamus induced by severe stress in animal model

Psychological stress induces many diseases including post-traumatic stress disorder (PTSD); however, the causal relationship between stress and brain atrophy has not been clarified. Applying single-prolonged stress (SPS) to explore the global effect of severe stress, we performed brain magnetic resonance imaging (MRI) acquisition and Voxel-based morphometry (VBM). Significant atrophy was detected in the bilateral thalamus and right visual cortex. Fluorescent immunohistochemistry for Iba-1 as the marker of activated microglia indicates regional microglial activation as stress-reaction in these atrophic areas. These data certify the impact of severe psychological stress on the atrophy of the visual cortex and the thalamus. Unexpectedly, these results are similar to chronic neuropathic pain rather than PTSD clinical research. We believe that some sensitisation mechanism from severe stress-induced atrophy in the visual cortex and thalamus, and the functional defect of the visual system may be a potential therapeutic target for stress-related diseases.

Comparative Anatomy of Gastrin-releasing Peptide Pathways in the Trigeminal Sensory System of Mouse and the Asian House Musk Shrew Suncus murinus

Gastrin-releasing peptide (GRP) has recently been identified as an itch-signaling molecule in the primary afferents and spinal cord of rodents. However, little information exists on the expression and localization of GRP in the trigeminal somatosensory system other than in rats. We examined the generality of the trigeminal GRP system in mammals using two distinct species, suncus as a model of specialized placental mammals known to have a well-developed trigeminal sensory system and mice as a representative small laboratory animal. We first analyzed the gross morphology of the trigeminal somatosensory system in suncus to provide a brainstem atlas on which to map GRP distribution. Immunohistochemical analyses showed that 8% of trigeminal ganglion neurons in suncus and 6% in mice expressed GRP. Expression was restricted to cells with smaller somata. The GRP-containing fibers were densely distributed in the superficial layers of the caudal part of the trigeminal spinal nucleus (Vc) but rare in the rostral parts, both in suncus and mice. Expression of GRP receptor mRNA and protein was also detected in the Vc of suncus. Taken together, these results suggest that the trigeminal GRP system mediating itch sensation is conserved in mammals.

Perinatal testosterone exposure is critical for the development of the male-specific sexually dimorphic gastrin-releasing peptide system in the lumbosacral spinal cord that mediates erection and ejaculation

Background

In rats, a sexually dimorphic spinal gastrin-releasing peptide (GRP) system in the lumbosacral spinal cord projects to spinal centers that control erection and ejaculation. This system controls the sexual function of adult males in an androgen-dependent manner. In the present study, we assessed the influence of androgen exposure on the spinal GRP system during a critical period of the development of sexual dimorphism.

Methods

Immunohistochemistry was used to determine if the development of the spinal GRP system is regulated by the perinatal androgen surge. We first analyzed the responses of neonates administered with anti-androgen flutamide. To remove endogenous androgens, rats were castrated at birth. Further, neonatal females were administered androgens during a critical period to evaluate the development of the male-specific spinal GRP system.

Results

Treatment of neonates with flutamide on postnatal days 0 and 1 attenuated the spinal GRP system during adulthood. Castrating male rats at birth resulted in a decrease in the number of GRP neurons and the intensity of neuronal GRP in the spinal cord during adulthood despite testosterone supplementation during puberty. This effect was prevented if the rats were treated with testosterone propionate immediately after castration. Moreover, treating female rats with androgens on the day of birth and the next day, masculinized the spinal GRP system during adulthood, which resembled the masculinized phenotype of adult males and induced a hypermasculine appearance.

Conclusions

The perinatal androgen surge plays a key role in masculinization of the spinal GRP system that controls male sexual behavior. Further, the present study provides potentially new approaches to treat sexual disorders of males.

Gout is associated with organic and psychogenic erectile dysfunction

BACKGROUND

Gout is a deposition disease with an inflammatory response that can increase the risk of cardiovascular disease. Gout is stressful for affected individuals, and can cause erectile dysfunction (ED). The objective of this study was to identify the association between gout and psychogenic ED (PED) and organic ED (OED).

METHOD

We analyzed 35,265 patients from the National Health Insurance Research Database who had been diagnosed with gout between 2000 and 2011. A total of 70,529 matched controls were included in the study as a comparison. Patients with a history of PED and OED occurring before the index date, aged less than 20 years, or with incomplete demographic information were excluded. Control patients were selected from the population of people without a history of gout, PED, or OED. The following risk factors for PED and OED were included as covariates in the multivariable models: age, comorbidities of coronary artery disease (CAD), peripheral arterial disease, chronic kidney disease (CKD), hypertension, diabetes, hyperlipidemia, depression and anxiety.

RESULT

Men with gout were more likely to have an increased risk (1.21 times) of ED than were those without gout. Patients with gout were 1.52 times more likely to develop OED and 1.18 times more likely to develop PED than patients in the control group. The risk of developing ED was greater for patients with comorbidities of CKD, diabetes, hyperlipidemia, depression and anxiety.

CONCLUSION

Gout is associated with organic and psychogenic ED. Clinical physicians should consider this association when treating patients with gout.

The Gastrin-Releasing Peptide Receptor (GRPR) in the Spinal Cord as a Novel Pharmacological Target

Gastrin-releasing peptide (GRP) is a mammalian neuropeptide that acts through the G protein-coupled receptor, GRP receptor (GRPR). Increasing evidence indicates that GRPR-mediated signaling in the central nervous system plays an important role in many physiological processes in mammals. Additionally, we have recently reported that the GRP system within the lumbosacral spinal cord not only controls erection but also triggers ejaculation in male rats. This system of GRP neurons is sexually dimorphic, being prominent in male rats but vestigial or absent in females. It is suggested that the sexually dimorphic GRP/GRPR system in the lumbosacral spinal cord plays a critical role in the regulation of male sexual function. In parallel, it has been reported that the somatosensory GRP/GRPR system in the spinal cord contributes to the regulation of itch specific transmission independently of the pain transmission. Interestingly, these two distinct functions in the same spinal region are both regulated by the neuropeptide, GRP. In this report, we review findings on recently identified GRP/GRPR systems in the spinal cord. These GRP/GRPR systems in the spinal cord provide new insights into pharmacological treatments for psychogenic erectile dysfunction as well as for chronic pruritus.

Expression and function of gastrin-releasing peptide (GRP) in normal and cancerous urological tissues

Gastrin-releasing peptide (GRP) acts as an important regulatory peptide in several normal physiological processes and as a growth factor in certain cancers. In this review we provide a comprehensive overview of the current state of knowledge of GRP in urological tissues under both normal and cancerous conditions. GRP and its receptor, GRP-R, are expressed in the normal kidney and renal cancers. GRP can stimulate the growth of renal cancer cells. GRP and GRP-R are expressed in prostate cancer and GRP can stimulate the growth of prostate cancer cell lines. Importantly, GRP is a key neuroendocrine peptide, which may be involved in the progression of advanced prostate cancer and in the neuroendocrine differentiation of prostate cancer. Recent animal studies have shown that GRP and GRP-R are an integral part of male sexual function and play a crucial role in spinal control of erections and ejaculation.

A rare symptom in posttraumatic stress disorder: Spontaneous ejaculation

Patient: Male, 25

Final Diagnosis: Post Traumatic Stress Disorder

Symptoms: Insomnia • nightmares • spontaneous ejaculation

Medication: Paroxentine

Clinical Procedure: —

Specialty: Psychiatry

Spontaneous ejaculation in a wild Indo-Pacific bottlenose dolphin (Tursiops aduncus)

Spontaneous ejaculation, which is defined as the release of seminal fluids without apparent sexual stimulation, has been documented in boreoeutherian mammals. Here we report spontaneous ejaculation in a wild Indo-Pacific bottlenose dolphin (Tursiops aduncus), and present a video of this rare behavior. This is the first report of spontaneous ejaculation by an aquatic mammal, and the first video of this behavior in animals to be published in a scientific journal.

Gastrin-releasing peptide receptors in the central nervous system: role in brain function and as a drug target

Neuropeptides acting on specific cell membrane receptors of the G protein-coupled receptor (GPCR) superfamily regulate a range of important aspects of nervous and neuroendocrine function. Gastrin-releasing peptide (GRP) is a mammalian neuropeptide that binds to the GRP receptor (GRPR, BB2). Increasing evidence indicates that GRPR-mediated signaling in the central nervous system (CNS) plays an important role in regulating brain function, including aspects related to emotional responses, social interaction, memory, and feeding behavior. In addition, some alterations in GRP or GRPR expression or function have been described in patients with neurodegenerative, neurodevelopmental, and psychiatric disorders, as well as in brain tumors. Findings from preclinical models are consistent with the view that the GRPR might play a role in brain disorders, and raise the possibility that GRPR agonists might ameliorate cognitive and social deficits associated with neurological diseases, while antagonists may reduce anxiety and inhibit the growth of some types of brain cancer. Further preclinical and translational studies evaluating the potential therapeutic effects of GRPR ligands are warranted.

Ultrahigh voltage electron microscopy links neuroanatomy and neuroscience/neuroendocrinology

The three-dimensional (3D) analysis of anatomical ultrastructures is extremely important in most fields of biological research. Although it is very difficult to perform 3D image analysis on exact serial sets of ultrathin sections, 3D reconstruction from serial ultrathin sections can generally be used to obtain 3D information. However, this technique can only be applied to small areas of a specimen because of technical and physical difficulties. We used ultrahigh voltage electron microscopy (UHVEM) to overcome these difficulties and to study the chemical neuroanatomy of 3D ultrastructures. This methodology, which links UHVEM and light microscopy, is a useful and powerful tool for studying molecular and/or chemical neuroanatomy at the ultrastructural level.

Biology of mammalian bombesin-like peptides and their receptors

PURPOSE OF REVIEW

This review will highlight recent advances in the understanding of mammalian bombesin receptor-related pathophysiological roles in disease states and new insights into bombesin receptor pharmacology.

RECENT FINDINGS

Studies regarding bombesin-like peptides and mammalian bombesin receptor functions have demonstrated significant biological impact on a broad array of physiological and pathophysiological conditions. Pharmacological experiments in vitro and in vivo as well as utilization of genetic rodent models of the gastrin-releasing peptide receptor (GRP-R/BB2) and neuromedin B receptor (NMB-R/BB1) further delineated roles in memory and fear behavior, inhibition of tumor cell growth, mediating signals for pruritus and male reproductive behavior. All three mammalian bombesin receptors were shown to possess some role in the regulation of energy balance. Novel synthesis of selective high affinity agonists and antagonists of the orphan bombesin receptor subtype-3 (BRS-3/BB3) has been accomplished and will facilitate further studies using animal model systems.

SUMMARY

Mammalian bombesin receptors participate in the regulation of energy homeostasis and may represent an attractive target for pharmacological treatment of obesity and certain eating disorders. Novel pharmacological insights of bombesin-like peptides and the interaction with their respective receptors have been elucidated to aid future treatment and imaging of epithelial cell-derived tumors.

High-voltage electron microscopy reveals direct synaptic inputs from a spinal gastrin-releasing peptide system to neurons of the spinal nucleus of bulbocavernosus

The spinal nucleus of bulbocavernosus (SNB) is a sexually dimorphic motor nucleus located in the anterior horn of the fifth and sixth lumbar segments of the spinal cord that plays a significant role in male sexual function. We recently found that a sexually dimorphic expression of gastrin-releasing peptide (GRP) in the lumbar spinal cord regulates male copulatory reflexes. Although it is reported that these systems are both profoundly regulated by circulating androgen levels in male rats, no direct evidence has been reported regarding GRP synaptic inputs onto SNB motoneurons. The aim of the current study was to determine the axodendritic synaptic inputs of spinal GRP neurons to SNB motoneurons. Immunoelectron microscopy, combined with a retrograde tracing technique using high-voltage electron microscopy (HVEM), provided a three-dimensional visualization of synaptic contacts from the GRP system in the lumbar spinal cord onto SNB motoneurons. HVEM analysis clearly demonstrated that GRP-immunoreactive axon terminals directly contact dendrites that extend into the dorsal gray commissure from the SNB. These HVEM findings provide an ultrastructural basis for understanding how the spinal GRP system regulates male sexual behavior.

Androgen regulates the sexually dimorphic gastrin-releasing peptide system in the lumbar spinal cord that mediates male sexual function

A collection of neurons in the upper lumbar spinal cord of male rats projects to the lower lumbar spinal cord, releasing gastrin-releasing peptide (GRP) onto somatic and autonomic centers known to regulate male sexual reflexes such as erection and ejaculation. Because these reflexes are androgen dependent, we asked whether manipulating levels of androgen in adult rats would affect GRP expression in this spinal center. We found that castration resulted, 28 d later, in a profound decrease in the expression of GRP in the spinal cord, as reflected in immunocytochemistry and competitive ELISA for the protein as well as real-time quantitative PCR for the transcript. These effects were prevented if the castrates were treated with testosterone propionate. Genetically male (XY) rats with the dysfunctional testicular feminization allele for the androgen receptor (AR) displayed GRP mRNA and protein levels in the spinal cord similar to those of females, indicating that androgen normally maintains the system through AR. We saw no effect of castration or the testicular feminization allele on expression of the receptor for GRP in the spinal cord, but castration did reduce expression of AR transcripts within the spinal cord as revealed by real-time quantitative PCR and Western blots. Taken together, these results suggest that androgen signaling plays a pivotal role in the regulation of GRP expression in male lumbar spinal cord. A greater understanding of how androgen modulates the spinal GRP system might lead to new therapeutic approaches to male sexual dysfunction.

Gastrin-releasing peptide system in the spinal cord controls male sexual behaviour

The lumbar spinal cord contains local neural circuits that are important in regulating male sexual behaviours, but the molecular mechanisms underlying these systems remain elusive. Gastrin-releasing peptide (GRP) is a member of the bombesin-like peptide family first isolated from the porcine stomach. Despite extensive pharmacological studies on the activity of bombesin-like peptides administered to mammals, little is known about the physiological functions of GRP in the spinal cord. We review recent findings on a system of neurones in the upper lumbar spinal cord, within the recently reported ejaculation generator, projecting axons containing GRP to the lower lumbar spinal cord and innervating regions known to control erection and ejaculation.