Sexually dimorphic gastrin releasing peptide system in the spinal cord controls male reproductive functions

Krause corpuscles are genital vibrotactile sensors for sexual behaviours

Krause corpuscles, which were discovered in the 1850s, are specialized sensory structures found within the genitalia and other mucocutaneous tissues1-4. The physiological properties and functions of Krause corpuscles have remained unclear since their discovery. Here we report the anatomical and physiological properties of Krause corpuscles of the mouse clitoris and penis and their roles in sexual behaviour. We observed a high density of Krause corpuscles in the clitoris compared with the penis. Using mouse genetic tools, we identified two distinct somatosensory neuron subtypes that innervate Krause corpuscles of both the clitoris and penis and project to a unique sensory terminal region of the spinal cord. In vivo electrophysiology and calcium imaging experiments showed that both Krause corpuscle afferent types are A-fibre rapid-adapting low-threshold mechanoreceptors, optimally tuned to dynamic, light-touch and mechanical vibrations (40-80 Hz) applied to the clitoris or penis. Functionally, selective optogenetic activation of Krause corpuscle afferent terminals evoked penile erection in male mice and vaginal contraction in female mice, while genetic ablation of Krause corpuscles impaired intromission and ejaculation of males and reduced sexual receptivity of females. Thus, Krause corpuscles of the clitoris and penis are highly sensitive mechanical vibration detectors that mediate sexually dimorphic mating behaviours.

Function of gastrin-releasing peptide receptors in ocular itch transmission in the mouse trigeminal sensory system

The prevalence of allergic conjunctivitis in itchy eyes has increased constantly worldwide owing to environmental pollution. Currently, anti-allergic and antihistaminic eye drops are used; however, there are many unknown aspects about the neural circuits that transmit itchy eyes. We focused on the gastrin-releasing peptide (GRP) and GRP receptor (GRPR), which are reportedly involved in itch transmission in the spinal somatosensory system, to determine whether the GRP system is involved in itch neurotransmission of the eyes in the trigeminal sensory system. First, the instillation of itch mediators, such as histamine (His) and non-histaminergic itch mediator chloroquine (CQ), exhibited concentration-dependent high levels of eye scratching behavior, with a significant sex differences observed in the case of His. Histological analysis revealed that His and CQ significantly increased the neural activity of GRPR-expressing neurons in the caudal part of the spinal trigeminal nucleus of the medulla oblongata in GRPR transgenic mice. We administered a GRPR antagonist or bombesin-saporin to ablate GRPR-expressing neurons, followed by His or CQ instillation, and observed a decrease in CQ-induced eye-scratching behavior in the toxin experiments. Intracisternal administration of neuromedin C (NMC), a GRPR agonist, resulted in dose-dependent excessive facial scratching behavior, despite the absence of an itch stimulus on the face. To our knowledge, this is the first study to demonstrate that non-histaminergic itchy eyes were transmitted centrally via GRPR-expressing neurons in the trigeminal sensory system, and that NMC in the medulla oblongata evoked facial itching.

Prostaglandin E2 Induces Long-Lasting Inhibition of Noradrenergic Neurons in the Locus Coeruleus and Moderates the Behavioral Response to Stressors

Neuronal activity is modulated not only by inputs from other neurons but also by various factors, such as bioactive substances. Noradrenergic (NA) neurons in the locus coeruleus (LC-NA neurons) are involved in diverse physiological functions, including sleep/wakefulness and stress responses. Previous studies have identified various substances and receptors that modulate LC-NA neuronal activity through techniques including electrophysiology, calcium imaging, and single-cell RNA sequencing. However, many substances with unknown physiological significance have been overlooked. Here, we established an efficient screening method for identifying substances that modulate LC-NA neuronal activity through intracellular calcium ([Ca2+]i) imaging using brain slices. Using both sexes of mice, we screened 53 bioactive substances, and identified five novel substances: gastrin-releasing peptide, neuromedin U, and angiotensin II, which increase [Ca2+]i, and pancreatic polypeptide and prostaglandin D2, which decrease [Ca2+]i Among them, neuromedin U induced the greatest response in female mice. In terms of the duration of [Ca2+]i change, we focused on prostaglandin E2 (PGE2), since it induces a long-lasting decrease in [Ca2+]i via the EP3 receptor. Conditional knock-out of the receptor in LC-NA neurons resulted in increased depression-like behavior, prolonged wakefulness in the dark period, and increased [Ca2+]i after stress exposure. Our results demonstrate the effectiveness of our screening method for identifying substances that modulate a specific neuronal population in an unbiased manner and suggest that stress-induced prostaglandin E2 can suppress LC-NA neuronal activity to moderate the behavioral response to stressors. Our screening method will contribute to uncovering previously unknown physiological functions of uncharacterized bioactive substances in specific neuronal populations.SIGNIFICANCE STATEMENT Bioactive substances modulate the activity of specific neuronal populations. However, since only a limited number of substances with predicted effects have been investigated, many substances that may modulate neuronal activity have gone unrecognized. Here, we established an unbiased method for identifying modulatory substances by measuring the intracellular calcium signal, which reflects neuronal activity. We examined noradrenergic (NA) neurons in the locus coeruleus (LC-NA neurons), which are involved in diverse physiological functions. We identified five novel substances that modulate LC-NA neuronal activity. We also found that stress-induced prostaglandin E2 (PGE2) may suppress LC-NA neuronal activity and influence behavioral outcomes. Our screening method will help uncover previously overlooked functions of bioactive substances and provide insight into unrecognized roles of specific neuronal populations.

Bombesins: A New Frontier in Hybrid Compound Development

Recently, bombesin (BN) and its analogs have attracted much attention as excellent anticancer agents because they interact with specific receptors widely distributed on the surface of various cancer cells. However, their biological properties proceed far beyond this, given a broad spectrum of activity. Bombesin receptor ligands are effective drugs for the treatment of rheumatoid arthritis or gastrointestinal diseases. However, most diseases are complex, and the use of polytherapy may lead to pharmacokinetic and pharmacodynamic drug-drug interactions, resulting in side effects. Therefore, there is a need to develop effective compounds that also contain BN or its analogs, which are combined with other structural entities, thus generating a so-called hybrid drug. Hybrid drugs that contain bombesin pharmacophore(s) may be proposed as a solution to the problem of polytherapy or the lack of an effective cure. Such structures have now demonstrated the desired efficacy, though information on these aforementioned compounds is relatively scarce. Therefore, our paper aims to encourage researchers to focus on bombesins. Herein, we indicate that the hybrid approach should also be firmly applied to bombesins and the BN receptor family. This paper's structure is divided into two main sections demonstrating bombesins and their properties, as well as recent data on bombesin-based hybrid compounds and their potential usefulness in medicine. Overall, it refers to the discovery and synthesis of modified bombesin-based hybrid compounds.

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.

Chronic corticosterone exposure evokes itch hypersensitivity and sexual dysfunction in male rats: relationship between the two distinct gastrin-releasing peptide systems in the spinal cord

In today's society, people are subjected to many social stressors, and excessive chronic stress causes functional disruption of the neuroendocrine system and many diseases. Although the exacerbation of atopic dermatitis with symptoms of itching and erectile dysfunction is induced by chronic stress, the details of the mechanisms are unknown. Here, we examined the effects of chronic stress on itch sensation and male sexual function at the behavioral and molecular levels, focusing on two distinct gastrin-releasing peptide (GRP) systems that independently regulate itch transmission, i.e., the somatosensory GRP system, and male sexual function, i.e., the lumbosacral autonomic GRP system, in the spinal cord. In a rat model of chronic stress induced by chronic corticosterone (CORT) administration, we observed increased plasma CORT concentrations, decreased body weight, and increased anxiety-like behavior, similar to that observed in humans. Chronic CORT exposure induced hypersensitivity to itch and increased the Grp mRNA level in the spinal somatosensory system, but there was no change in pain or tactile sensitivity. Antagonists of the somatosensory GRP receptor, an itch-specific mediator, suppressed itch hypersensitivity induced by chronic CORT exposure. In contrast, chronic CORT exposure decreased male sexual behavior, ejaculated semen volume, vesicular gland weight, and plasma testosterone levels. However, there were no effects on the expression of Grp mRNA or protein in the lumbosacral autonomic GRP system, which regulates male sexual function. In summary, chronic stress model rats showed itch hypersensitivity and impaired sexual function in males, and the involvement of the spinal GRP systems was apparent in itch hypersensitivity.

Understanding and treating ejaculatory dysfunction in men with diabetes mellitus

Diabetes mellitus is a rapidly rising metabolic disorder with important systemic complications. Global figures have demonstrated the prevalence of diabetes mellitus has almost quadrupled from 108 million in 1980 to 422 million in 2014, with a current prevalence of over 525 million. Of the male sexual dysfunction resulting from diabetes mellitus, significant focus is afforded to erectile dysfunction. Nevertheless, ejaculatory dysfunction constitutes important sexual sequelae in diabetic men, with up to 35%-50% of men with diabetes mellitus suffering from ejaculatory dysfunction. Despite this, aspects of its pathophysiology and treatment are less well understood than erectile dysfunction. The main disorders of ejaculation include premature ejaculation, delayed ejaculation, anejaculation and retrograde ejaculation. Although ejaculatory dysfunction in diabetes mellitus can have complex multifactorial aetiology, understanding its pathophysiological mechanisms has facilitated the development of therapies in the management of ejaculatory dysfunction. Most of our understanding of its pathophysiology is derived from diabetic animal models; however, observational studies in humans have also provided useful information in elucidating important associative factors potentially contributing to ejaculatory dysfunction in diabetic men. These have provided the potential for more tailored treatment regimens in patients depending on the ejaculatory disorder, other co-existing sequelae of diabetes mellitus, specific metabolic factors as well as the need for fertility treatment. However, evidence for treatment of ejaculatory dysfunction, especially delayed ejaculation and retrograde ejaculation, is based on low-level evidence comprising small sample-size series and retrospective or cross-sectional studies. Whilst promising findings from large randomised controlled trials have provided strong evidence for the licensed treatment of premature ejaculation, similar robust studies are needed to accurately elucidate factors predicting ejaculatory dysfunction in diabetes mellitus, as well as for the development of pharmacotherapies for delayed ejaculation and retrograde ejaculation. Similarly, more contemporary robust data are required for fertility outcomes in these patients, including methods of sperm retrieval and assisted reproductive techniques in retrograde ejaculation.

Characterization of the expression of gastrin-releasing peptide and its receptor in the trigeminal and spinal somatosensory systems of Japanese macaque monkeys: Insight into humans

Gastrin-releasing peptide (GRP) and its receptor (GRPR) have been identified as itch mediators in the spinal and trigeminal somatosensory systems in rodents. In primates, there are few reports of GRP/GRPR expression or function in the spinal sensory system and virtually nothing is known in the trigeminal system. The aim of the present study was to characterize GRP and GRPR in the trigeminal and spinal somatosensory system of Japanese macaque monkeys (Macaca fuscata). cDNA encoding GRP was isolated from the macaque dorsal root ganglion (DRG) and exhibited an amino acid sequence that was highly conserved among mammals and especially in primates. Immunohistochemical analysis demonstrated that GRP was expressed mainly in the small-sized trigeminal ganglion and DRG in adult macaque monkeys. Densely stained GRP-immunoreactive (ir) fibers were observed in superficial layers of the spinal trigeminal nucleus caudalis (Sp5C) and the spinal cord. In contrast, GRP-ir fibers were rarely observed in the principal sensory trigeminal nucleus and oral and interpolar divisions of the spinal trigeminal nucleus. cDNA cloning, in situ hybridization, and Western blot revealed substantial expression of GRPR mRNA and GRPR protein in the macaque spinal dorsal horn and Sp5C. Our Western ligand blot and ligand derivative stain for GRPR revealed that GRP directly bound in the macaque Sp5C and spinal dorsal horn as reported in rodents. Finally, GRP-ir fibers were also detected in the human spinal dorsal horn. The spinal and trigeminal itch neural circuits labeled with GRP and GRPR appear to function also in primates.

Neurons for Ejaculation and Factors Affecting Ejaculation

Simple Summary

Sexual dysfunctions are rarely discussed in our current society. Males experience different sexual dysfunctions, including erectile, infertility, and ejaculatory dysfunctions. In this review only the ejaculatory dysfunction will be discussed. Ejaculation is defined as the ejection of contents collectively from the vas deferens, seminal vesicle, prostate and Cowper’s glands. It is completely controlled by a population of neurons present in the lumbar spinal cord. The presence of lesion in these neurons ceases the ejaculatory behavior in males. This population of neurons was first identified in rats; however, recently it was confirmed that these neurons are present in human males as well. The issues are known as ejaculatory dysfunction. The following are the different types of ejaculatory dysfunctions: early ejaculation, ejaculation into the urinary bladder, late ejaculation and no ejaculation.

Abstract

Ejaculation is a reflex and the last stage of intercourse in male mammals. It consists of two coordinated phases, emission and expulsion. The emission phase consists of secretions from the vas deferens, seminal vesicle, prostate, and Cowper’s gland. Once these contents reach the posterior urethra, movement of the contents becomes inevitable, followed by the expulsion phase. The urogenital organs are synchronized during this complete event. The L3–L4 (lumbar) segment, the spinal cord region responsible for ejaculation, nerve cell bodies, also called lumbar spinothalamic (LSt) cells, which are denoted as spinal ejaculation generators or lumbar spinothalamic cells [Lst]. Lst cells activation causes ejaculation. These Lst cells coordinate with [autonomic] parasympathetic and sympathetic assistance in ejaculation. The presence of a spinal ejaculatory generator has recently been confirmed in humans. Different types of ejaculatory dysfunction in humans include premature ejaculation (PE), retrograde ejaculation (RE), delayed ejaculation (DE), and anejaculation (AE). The most common form of ejaculatory dysfunction studied is premature ejaculation. The least common forms of ejaculation studied are delayed ejaculation and anejaculation. Despite the confirmation of Lst in humans, there is insufficient research on animals mimicking human ejaculatory dysfunction.

Vasopressin-oxytocin-type signaling is ancient and has a conserved water homeostasis role in euryhaline marine planarians

Vasopressin/oxytocin (VP/OT)-related peptides are essential for mammalian antidiuresis, sociosexual behavior, and reproduction. However, the evolutionary origin of this peptide system is still uncertain. Here, we identify orthologous genes to those for VP/OT in Platyhelminthes, intertidal planarians that have a simple bilaterian body structure but lack a coelom and body-fluid circulatory system. We report a comprehensive characterization of the neuropeptide derived from this VP/OT-type gene, identifying its functional receptor, and name it the "platytocin" system. Our experiments with these euryhaline planarians, living where environmental salinities fluctuate due to evaporation and rainfall, suggest that platytocin functions as an "antidiuretic hormone" and also organizes diverse actions including reproduction and chemosensory-associated behavior. We propose that bilaterians acquired physiological adaptations to amphibious lives by such regulation of the body fluids. This neuropeptide-secreting system clearly became indispensable for life even without the development of a vascular circulatory system or relevant synapses.

Transcription factor gene Pea3 regulates erectile function during copulation in mice

Male mice with homozygous loss of function mutations of the transcription factor gene Pea3 (Pea3 null) are infertile due to their inability to inseminate females, however the specific deficits in male sexual behaviors that drive this phenotype are unknown. Here, the copulatory behavior of male mice (Pea3 null and control) with hormonally primed ovariectomized females was monitored via high-speed and high-resolution digital videography to assess for differences in female-directed social behaviors, gross sexual behaviors (mounting, thrusting), and erectile and ejaculatory function. Pea3 null male mice exhibit greatly reduced erectile function, with 44% of males displaying no visible erections during copulation, and 0% achieving sustained erections. As such, Pea3 null males are incapable of intromission and copulatory plug deposition, despite displaying largely normal female-directed social behaviors, mounting behaviors, and ejaculatory grasping behavior. Additionally, the organization and timing of thrusting behaviors is impaired in Pea3 null males. Our results show that the transcription factor gene Pea3 regulates the ability to achieve and maintain erections during copulation in mice.

Sexual Experience Induces the Expression of Gastrin-Releasing Peptide and Oxytocin Receptors in the Spinal Ejaculation Generator in Rats

Male sexual function in mammals is controlled by the brain neural circuits and the spinal cord centers located in the lamina X of the lumbar spinal cord (L3–L4). Recently, we reported that hypothalamic oxytocin neurons project to the lumbar spinal cord to activate the neurons located in the dorsal lamina X of the lumbar spinal cord (dXL) via oxytocin receptors, thereby facilitating male sexual activity. Sexual experiences can influence male sexual activity in rats. However, how this experience affects the brain–spinal cord neural circuits underlying male sexual activity remains unknown. Focusing on dXL neurons that are innervated by hypothalamic oxytocinergic neurons controlling male sexual function, we examined whether sexual experience affects such neural circuits. We found that >50% of dXL neurons were activated in the first ejaculation group and ~30% in the control and intromission groups in sexually naïve males. In contrast, in sexually experienced males, ~50% of dXL neurons were activated in both the intromission and ejaculation groups, compared to ~30% in the control group. Furthermore, sexual experience induced expressions of gastrin-releasing peptide and oxytocin receptors in the lumbar spinal cord. This is the first demonstration of the effects of sexual experience on molecular expressions in the neural circuits controlling male sexual activity in the spinal cord.

Oxytocin, Erectile Function and Sexual Behavior: Last Discoveries and Possible Advances

A continuously increasing amount of research shows that oxytocin is involved in numerous central functions. Among the functions in which oxytocin is thought to be involved are those that play a role in social and sexual behaviors, and the involvement of central oxytocin in erectile function and sexual behavior was indeed one of the first to be discovered in laboratory animals in the 1980s. The first part of this review summarizes the results of studies done in laboratory animals that support a facilitatory role of oxytocin in male and female sexual behavior and reveal mechanisms through which this ancient neuropeptide participates in concert with other neurotransmitters and neuropeptides in this complex function, which is fundamental for the species reproduction. The second part summarizes the results of studies done mainly with intranasal oxytocin in men and women with the aim to translate the results found in laboratory animals to humans. Unexpectedly, the results of these studies do not appear to confirm the facilitatory role of oxytocin found in male and female sexual behavior in animals, both in men and women. Possible explanations for the failure of oxytocin to improve sexual behavior in men and women and strategies to attempt to overcome this impasse are considered.

The gastrin-releasing peptide/bombesin system revisited by a reverse-evolutionary study considering Xenopus

Bombesin is a putative antibacterial peptide isolated from the skin of the frog, Bombina bombina. Two related (bombesin-like) peptides, gastrin-releasing peptide (GRP) and neuromedin B (NMB) have been found in mammals. The history of GRP/bombesin discovery has caused little attention to be paid to the evolutionary relationship of GRP/bombesin and their receptors in vertebrates. We have classified the peptides and their receptors from the phylogenetic viewpoint using a newly established genetic database and bioinformatics. Here we show, by using a clawed frog (Xenopus tropicalis), that GRP is not a mammalian counterpart of bombesin and also that, whereas the GRP system is widely conserved among vertebrates, the NMB/bombesin system has diversified in certain lineages, in particular in frog species. To understand the derivation of GRP system in the ancestor of mammals, we have focused on the GRP system in Xenopus. Gene expression analyses combined with immunohistochemistry and Western blotting experiments demonstrated that GRP peptides and their receptors are distributed in the brain and stomach of Xenopus. We conclude that GRP peptides and their receptors have evolved from ancestral (GRP-like peptide) homologues to play multiple roles in both the gut and the brain as one of the ‘gut-brain peptide’ systems.

Spinal Cord Injury Causes Reduction of Galanin and Gastrin Releasing Peptide mRNA Expression in the Spinal Ejaculation Generator of Male Rats

Spinal cord injury (SCI) in men is commonly associated with sexual dysfunction, including anejaculation, and chronic mid-thoracic contusion injury in male rats also impairs ejaculatory reflexes. Ejaculation is controlled by a spinal ejaculation generator consisting of a population of lumbar spinothalamic (LSt) neurons that control ejaculation through release of four neuropeptides including galanin and gastrin releasing peptide (GRP) onto lumbar and sacral autonomic and motor nuclei. It was recently demonstrated that spinal contusion injury in male rats caused reduction of GRP-immunoreactivity, but not galanin-immunoreactivity in LSt cells, indicative of reduced GRP peptide levels, but inconclusive results for galanin. The current study further tests the hypothesis that contusion injury causes a disruption of GRP and galanin mRNA in LSt cells. Male rats received mid-thoracic contusion injury and galanin and GRP mRNA were visualized 8 weeks later in the lumbar spinal cord using fluorescent in situ hybridization. Spinal cord injury significantly reduced GRP and galanin mRNA in LSt cells. Galanin expression was higher in LSt cells compared to GRP. However, expression of the two transcripts were positively correlated in LSt cells in both sham and SCI animals, suggesting that expression for the two neuropeptides may be co-regulated. Immunofluorescent visualization of galanin and GRP peptides demonstrated a significant reduction in GRP-immunoreactivity, but not galanin in LSt cells, confirming the previous observations. In conclusion, SCI reduced GRP and galanin expression in LSt cells with an apparent greater impact on GRP peptide levels. GRP and galanin are both essential for triggering ejaculation and thus such reduction may contribute to ejaculatory dysfunction following SCI in rats.

Variation of pro-vasopressin processing in parvocellular and magnocellular neurons in the paraventricular nucleus of the hypothalamus: Evidence from the vasopressin-related glycopeptide copeptin

Arginine vasopressin (AVP) is synthesized in parvocellular- and magnocellular neuroendocrine neurons in the paraventricular nucleus (PVN) of the hypothalamus. Whereas magnocellular AVP neurons project primarily to the posterior pituitary, parvocellular AVP neurons project to the median eminence (ME) and to extrahypothalamic areas. The AVP gene encodes pre-pro-AVP that comprises the signal peptide, AVP, neurophysin (NPII), and a copeptin glycopeptide. In the present study, we used an N-terminal copeptin antiserum to examine copeptin expression in magnocellular and parvocellular neurons in the hypothalamus in the mouse, rat, and macaque monkey. Although magnocellular NPII-expressing neurons exhibited strong N-terminal copeptin immunoreactivity in all three species, a great majority (~90%) of parvocellular neurons that expressed NPII was devoid of copeptin immunoreactivity in the mouse, and in approximately half (~53%) of them in the rat, whereas in monkey hypothalamus, virtually all NPII-immunoreactive parvocellular neurons contained strong copeptin immunoreactivity. Immunoelectron microscopy in the mouse clearly showed copeptin-immunoreactivity co-localized with NPII-immunoreactivity in neurosecretory vesicles in the internal layer of the ME and posterior pituitary, but not in the external layer of the ME. Intracerebroventricular administration of a prohormone convertase inhibitor, hexa-d-arginine amide resulted in a marked reduction of copeptin-immunoreactivity in the NPII-immunoreactive magnocellular PVN neurons in the mouse, suggesting that low protease activity and incomplete processing of pro-AVP could explain the disproportionally low levels of N-terminal copeptin expression in rodent AVP (NPII)-expressing parvocellular neurons. Physiologic and phylogenetic aspects of copeptin expression among neuroendocrine neurons require further exploration.

Systemic effects of oxytocin on male sexual activity via the spinal ejaculation generator in rats

Oxytocin is produced in the hypothalamus and stimulates uterine contraction and milk ejection. While many people consider oxytocin to be a female hormone, it is reported that, in men, the plasma oxytocin level increases markedly after ejaculation. However, this aspect of oxytocin physiology is poorly understood. The spinal ejaculation generator (SEG), which expresses the neuropeptide, gastrin-releasing peptide (GRP), can trigger ejaculation in rats. Therefore, we focused on systemic effects of oxytocin on the GRP/SEG neuron system in the lumbar spinal cord controlling sexual activity in male rats. We found that systemic administration of oxytocin significantly shortened the latency to the first mount, intromission and ejaculation during male copulatory behavior. In addition, the local oxytocin level in the lumbar cord was significantly higher in males than in females. Histological analysis showed that oxytocin-binding is apparent in spinal GRP/SEG neurons. We therefore conclude that oxytocin influences male sexual activity via the SEG.

In Vivo Electrophysiology of Peptidergic Neurons in Deep Layers of the Lumbar Spinal Cord after Optogenetic Stimulation of Hypothalamic Paraventricular Oxytocin Neurons in Rats

The spinal ejaculation generator (SEG) is located in the central gray (lamina X) of the rat lumbar spinal cord and plays a pivotal role in the ejaculatory reflex. We recently reported that SEG neurons express the oxytocin receptor and are activated by oxytocin projections from the paraventricular nucleus of hypothalamus (PVH). However, it is unknown whether the SEG responds to oxytocin in vivo. In this study, we analyzed the characteristics of the brain–spinal cord neural circuit that controls male sexual function using a newly developed in vivo electrophysiological technique. Optogenetic stimulation of the PVH of rats expressing channel rhodopsin under the oxytocin receptor promoter increased the spontaneous firing of most lamina X SEG neurons. This is the first demonstration of the in vivo electrical response from the deeper (lamina X) neurons in the spinal cord. Furthermore, we succeeded in the in vivo whole-cell recordings of lamina X neurons. In vivo whole-cell recordings may reveal the features of lamina X SEG neurons, including differences in neurotransmitters and response to stimulation. Taken together, these results suggest that in vivo electrophysiological stimulation can elucidate the neurophysiological response of a variety of spinal neurons during male sexual behavior.

Genome-wide prediction and comparative transcriptomic analysis reveals the G protein-coupled receptors involved in gonadal development of Apostichopus japonicus

The sea cucumber Apostichopus japonicus is dioecious, with seasonal reproduction. G protein-coupled receptor (GPCR)-mediated signaling systems might play critical roles in the reproductive control of A. japonicus. Here, we classified GPCR from the genome in silico and used transcriptomic analyses to further mine those that function in gonadal-development control. Totally, 487 GPCRs were predicted from A. japonicus, and 183 of these were further annotated to molecular pathways. Transcriptome analysis revealed 327 GPCRs expressed in gonads, and these were classified into four families and 19 subfamilies. Three pathways were apparently associated with reproduction, including neuroactive ligand-receptor interaction, the mTOR and Wnt signaling pathways. Seven and eight ovary- and testis-specific GPCRs were filtered, and the gene expression profiles were determined in multiple tissues and gonads at different developmental stages by qPCR. These results provide new insights into the discovery of GPCR-mediated signaling control in sea cucumber reproduction, especially in gonadal development control.

Oxytocin Influences Male Sexual Activity via Non-synaptic Axonal Release in the Spinal Cord

Oxytocinergic neurons in the paraventricular nucleus of the hypothalamus that project to extrahypothalamic brain areas and the lumbar spinal cord play an important role in the control of erectile function and male sexual behavior in mammals. 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)." We have examined the functional interaction between the SEG neurons and the hypothalamo-spinal oxytocin system in rats. Here, we show that SEG/GRP neurons express oxytocin receptors and are activated by oxytocin during male sexual behavior. Intrathecal injection of oxytocin receptor antagonist not only attenuates ejaculation but also affects pre-ejaculatory behavior during normal sexual activity. Electron microscopy of potassium-stimulated acute slices of the lumbar cord showed that oxytocin-neurophysin-immunoreactivity was detected in large numbers of neurosecretory dense-cored vesicles, many of which are located close to the plasmalemma of axonal varicosities in which no electron-lucent microvesicles or synaptic membrane thickenings were visible. These results suggested that, in rats, release of oxytocin in the lumbar spinal cord is not limited to conventional synapses but occurs by exocytosis of the dense-cored vesicles from axonal varicosities and acts by diffusion-a localized volume transmission-to reach oxytocin receptors on GRP neurons and facilitate male sexual function.

Lumbar spinal cord neurons putatively involved in ejaculation are sexually dimorphic in early postnatal mice

A crucial role in ejaculation is thought to be played by a population of lumbar spino-thalamic neurons (LSt), which express galanin and other neuropeptides. In rats, these neurons are activated with ejaculation and their lesion selectively abolishes ejaculation but not other mating behaviors. Consistently with their role, in adult rats and humans, LSt neurons are sexually dimorphic, being more numerous in males. Here we examined whether sexual dimorphism arises early in development, using a transgenic mouse line in which the expression of fluorescent protein is driven by the galanin promoter. We focused on postnatal day 4, shortly after a transient perinatal androgen surge in males that could play an organizational role in LSt development. We found a population of brightly fluorescent neurons organized in bilateral columns dorsolateral to the central canal in segments L1-L5, the expected location of the LSt group. Their number was close to that of adult preparations and significantly greater in male than in female siblings (+19%; CI_95% : +13% to +27%; p < .01). This was not due to a generalized higher galanin expression in the male since fluorescent L4 DRG neurons, innervating the hindlimbs and lower back, were not significantly dimorphic (-4%; CI_95% : -10% to +8%; p = .92). Unexpectedly, we found in cervical segments a population of fluorescent neurons having a location relative to the central canal similar to the LSt. Thus, the LSt group is sexually dimorphic soon after birth. However, it is possible that only a subset of its neurons participate in the control of ejaculation.

Chronic Spinal Cord Injury Reduces Gastrin-Releasing Peptide in the Spinal Ejaculation Generator in Male Rats

Spinal cord injury (SCI) causes sexual dysfunction, including anejaculation in men. Likewise, chronic mid-thoracic contusion injury impairs ejaculatory reflexes in male rats. Ejaculation is controlled by a spinal ejaculation generator (SEG) comprised of a population of lumbar spinothalamic (LSt) neurons. LSt neurons co-express four neuropeptides, including gastrin-releasing peptide (GRP) and galanin and control ejaculation via release of these peptides in lumbar and sacral autonomic and motor nuclei. Here, we tested the hypothesis that contusion injury causes a disruption of the neuropeptides that are expressed in LSt cell bodies and axon terminals, thereby causing ejaculatory dysfunction. Male Sprague Dawley rats received contusion or sham surgery at spinal levels T6-7. Five to six weeks later, animals were perfused and spinal cords were immunoprocessed for galanin and GRP. Results showed that numbers of cells immunoreactive for galanin were not altered by SCI, suggesting that LSt cells are not ablated by SCI. In contrast, GRP immunoreactivity was decreased in LSt cells following SCI, evidenced by fewer GRP and galanin/GRP dual labeled cells. However, SCI did not affect efferent connections of LSt, cells as axon terminals containing galanin or GRP in contact with autonomic cells were not reduced following SCI. Finally, no changes in testosterone plasma levels or androgen receptor expression were noted after SCI. In conclusion, chronic contusion injury decreased immunoreactivity for GRP in LSt cell soma, but did not affect LSt neurons per se or LSt connections within the SEG. Since GRP is essential for triggering ejaculation, such loss may contribute to ejaculatory dysfunction following SCI.

Role of the androgen receptor in the central nervous system

The involvement of gonadal androgens in functions of the central nervous system was suggested for the first time about half a century ago. Since then, the number of functions attributed to androgens has steadily increased, ranging from regulation of the hypothalamic-pituitary-gonadal axis and reproductive behaviors to modulation of cognition, anxiety and other non-reproductive functions. This review focuses on the implication of the neural androgen receptor in these androgen-sensitive functions and behaviors.

Effects of Sex Steroids on the Spinal Gastrin-Releasing Peptide System Controlling Male Sexual Function in Rats

The gastrin-releasing peptide (GRP) system in the lumbosacral spinal cord controls male sexual function in rats. In contrast, in female rats, GRP neurons could scarcely be detected around puberty when circulating ovarian steroid hormones such as estradiol and progesterone levels are increasing. However, little information is available on feminizing or demasculinizing effects of ovarian steroids on the central nervous system in female puberty and adulthood. In this study, to visualize the spinal GRP neurons in vivo, we generated a GRP-promoter-Venus transgenic (Tg) rat line and studied the effects of the sex steroid hormones on GRP expression in the rat lumbar cord by examining the Venus fluorescence. In these Tg rats, the sexually dimorphic spinal GRP neurons controlling male sexual function were clearly labeled with Venus fluorescence. As expected, Venus fluorescence in the male lumbar cord was markedly decreased after castration and restored by chronic androgen replacement. Furthermore, androgen-induced Venus expression in the spinal cord of adult Tg males was significantly attenuated by chronic treatment with progesterone but not with estradiol. A luciferase assay using a human GRP-promoter construct showed that androgens enhance the spinal GRP system, and more strikingly, that progesterone acts to inhibit the GRP system via an androgen receptor-mediated mechanism. These results demonstrate that circulating androgens may play an important role in the spinal GRP system controlling male sexual function not only in rats but also in humans and that progesterone could be an important feminizing factor in the spinal GRP system in females during pubertal development.

A sexually dimorphic peptidergic system in the lower spinal cord controlling penile function in non-human primates

STUDY DESIGN

Experimental animal study.

OBJECTIVES

Although a population of gastrin-releasing peptide (GRP) neurons in the lumbar spinal cord has an important role in erection and ejaculation in rats, little information exists on this GRP system in primates. To identify the male-specific GRP system in the primate spinal cord, we studied the lumbosacral cord in macaque monkeys as a non-human primate model.

SETTING

University laboratory in Japan.

METHODS

To determine the gene sequence of GRP precursors, the rhesus macaque monkey genomic sequence data were searched, followed by phylogenetic analysis. Subsequently, immunocytochemical analysis for GRP was performed in the monkey spinal cord.

RESULTS

We have used bioinformatics to identify the ortholog gene for GRP precursor in macaque monkeys. Phylogenetic analysis suggested that primate prepro-GRP is separated from that of other mammalian species and clustered to an independent branch as primates. Immunocytochemistry for GRP further demonstrated that male-dominant sexual dimorphism was found in the spinal GRP system in monkeys as in rodents.

CONCLUSION

We have demonstrated in macaque monkeys that the GRP system in the lower spinal cord shows male-specific dimorphism and may have an important role in penile functions not only in rodents but also in primates.

SPONSORSHIP

Tissues of Nihonzaru (Japanese macaque monkeys) were provided in part by National Institutes of Natural Sciences (NINS) through the National Bio-Resource Project (NBRP) of the MEXT, Japan. This work was supported in part by KAKENHI from the Japan Society for the Promotion of Science (JSPS) (to KT; 15KK0343, 15J40220 and HS; 15K15202, 15KK0257, 15H05724).

A Placebo-Controlled Crossover Trial of Gastrin-Releasing Peptide in Childhood Autism

OBJECTIVES

The aim of this study was to evaluate the efficacy, safety, and tolerability of gastrin-releasing peptide (GRP) compared with placebo in autism spectrum disorder symptoms.

METHODOLOGY

This is a randomized, double-blind, placebo-controlled crossover trial using GRP 160 pmol/kg for 4 consecutive days in 10 children with autism. Outcomes were measured by the Aberrant Behavior Checklist (ABC) scale.

RESULTS

All participants were boys, aged between 4 and 9 years. There was a reduction in the scores of the ABC range and its subscales after use GRP and placebo. The reduction was more prominent with GRP, particularly in the subscale "hyperactivity and noncompliance," but there was no statistical difference between the results (P = 0.334). After a week of infusion, 5 children showed improvement of 25% or greater in the total score of the ABC scale with GRP use and 2 with placebo use; however, there was no statistical difference (P = 0.375). There were no adverse effects, changes in vital signs, or laboratory abnormalities associated with the use of GRP.

CONCLUSIONS

The results of this study, despite the small sample size, reinforce previous data on the safety of the GRP in short-term use. There is a need for further research with other designs and a larger sample size to evaluate the efficacy and safety of GRP in children with autism.

Spinal Mechanisms of Itch Transmission

Peripheral itch stimuli are transmitted by sensory neurons to the spinal cord dorsal horn, which then transmits the information to the brain. The molecular and cellular mechanisms within the dorsal horn for itch transmission have only been investigated and identified during the past ten years. This review covers the progress that has been made in identifying the peptide families in sensory neurons and the receptor families in dorsal horn neurons as putative itch transmitters, with a focus on gastrin-releasing peptide (GRP)-GRP receptor signaling. Also discussed are the signaling mechanisms, including opioids, by which various types of itch are transmitted and modulated, as well as the many conflicting results arising from recent studies.

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.

Human spinal ejaculation generator

OBJECTIVE

A spinal ejaculation generator (SEG) has been identified in the rat with lumbar galaninergic interneurons playing a pivotal role (Science 2002;297:1566-1569). The aim was to evidence a SEG in humans.

METHODS

Spatial distribution of galaninergic neurons was studied in postmortem spinal cord segments of 6 men and compared with that of 6 women for evidencing sexual dimorphism. Based on the identified segmental distribution of galaninergic neurons, the ability for penile vibratory stimulation (PVS) to elicit ejaculation when the concerned spinal segments were injured was studied in 384 patients with clinically complete spinal cord injury (SCI) and consequent anejaculation. Such patients represent a unique model to investigate the role of defined spinal segments in the control of ejaculation.

RESULTS

Galaninergic neurons were mostly located between L2 and L5 segments in medial lamina VII, with a maximal density within L4. Three-dimensional 3D reconstruction showed that these neurons were grouped into single columns bilaterally to the central canal. In addition, galaninergic neuron density was found higher in L3 and L4 segments in men as compared to women supporting sexual dimorphism. In the patients' cohort, injury of L3-L5 segments was the sole independent predictor for failure of PVS to induce ejaculation. Although evidence from clinical observations was indirect, there is close correspondence to neuroanatomical data.

INTERPRETATION

Organization and sexual dimorphism of human spinal galaninergic neurons were similar to the rat's SEG. Neurohistological data, together with clinical results, corroborate the existence of an SEG in humans in L3-L5 segments. Such a generator could be targeted to treat neurogenic and non-neurogenic ejaculatory disorders. ANN NEUROL 2017;81:35-45.

Physiology and Pharmacology of Ejaculation

Ejaculation is the final stage of coitus in mammalian male and is mandatory for natural procreation. Two synchronized phases, emission and expulsion, form the ejaculatory response and involve specific organs and anatomical structures. The peripheral events leading to ejaculation are commanded by autonomic (sympathetic and parasympathetic) and somatic divisions of the nervous system. The autonomic and somatic motor efferents originate in spinal nuclei located in thoracolumbar and lumbosacral segments. Co-ordinated activation of autonomic and somatic spinal nuclei is orchestrated by a group of lumbar spinal interneurons defined as the spinal generator of ejaculation. The generator of ejaculation together with the autonomic and somatic spinal nuclei constitutes a spinal network that is under the strong influence of stimulating or inhibiting genital sensory and supraspinal inputs. A brain circuitry dedicated to ejaculation has been delineated that is part of a more global network controlling other aspects of the sexual response. This circuitry includes discrete neuronal populations distributed in all divisions of the brain. The corollary to the expanded CNS network is the variety of neurotransmitter systems participating in the ejaculatory process. Among them, serotonin neurotransmission plays a key role and its targeting led to the development of the first registered pharmacological treatment of premature ejaculation in human beings. Critical gaps remain in the understanding of neurophysiopharmacology of ejaculation and management of ejaculatory disorders in human beings needs improvement. Because the ejaculatory response in laboratory animals and in human beings shares many similarities, the use of animal models will certainly provide further advances in the field.

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.

Postnatal development of the gastrin-releasing peptide system in the lumbosacral spinal cord controlling male reproductive function in rats

A sexually dimorphic spinal gastrin-releasing peptide (GRP) system in the lumbosacral spinal cord, which projects to the lower spinal centers, controls erection and ejaculation in rats. However, little is known about the postnatal development of this system. In this study, we therefore examined the postnatal development of the male-dominant spinal GRP system and its sexual differentiation in rats using immunohistochemistry. Our results show that male-dominant expression of GRP is prominent from the onset of puberty and that sexually dimorphism persists into adulthood. These results suggest that androgen surge during male puberty plays an important role in the development and maintenance of the male-specific GRP function in the rat spinal cord.

Visualization of Kisspeptin Binding to Rat Hypothalamic Neurons

The neuropeptide kisspeptin plays an important role in fertility and the onset of puberty, stimulating gonadotropin-releasing hormone (GnRH) neurons to activate the hypothalamic–pituitary–gonadal axis. Several studies have demonstrated a morphological interaction between kisspeptin- and GnRH-expressing neurons; however, few have addressed the interaction of kisspeptin with other neuronal subtypes. We recently showed that fibers immunoreactive for kisspeptin were densely distributed in the dorsal part of the arcuate nucleus. These fibers were found in close proximity to GnRH and tuberoinfundibular dopamine (TIDA) neurons. In the present study, using biotinylated kisspeptin, we established a visualization method for identifying kisspeptin binding sites on TIDA neurons. Biotinylated kisspeptin bound to the cell bodies of TIDA neurons and surrounding fibers, suggesting that TIDA neurons express sites of action for kisspeptin. Our assay also detected biotinylation signals from kisspeptin binding to GnRH fibers in the median eminence, but not to cell bodies of GnRH neurons in the medial preoptic area. Positive signals were completely eliminated by addition of excess non-labeled kisspeptin. This method enabled us to detect kisspeptin binding sites on specific neural structures and neuronal fibers.

Three-dimensional visualization of multiple synapses in thick sections using high-voltage electron microscopy in the rat spinal cord

This data article contains complementary figure and movies (Supplementary Movies 1-3) related to the research article entitled, "Effective synaptome analysis of itch-mediating neurons in the spinal cord: a novel immunohistochemical methodology using high-voltage electron microscopy" [7]. It is important to show the synaptic connections at the ultrastructural level to understand the neural circuit, which requires the three-dimensional (3-D) analyses in the electron microscopy. Here, we applied a new sample preparation method, a high-contrast en bloc staining according to the protocol of the National Center for Microscopy and Imaging Research (NCMIR), University of California, San Diego, CA, USA to high-voltage electron microscopy (HVEM) tomography in order to examine the 3-D chemical neuroanatomy of the rat spinal cord. Pre-embedding immunoelectron microscopy was used in this study. HVEM has an excellent potential to directly visualize the ultrastructures in semi-thin sections (~5 μm thick), and we have successfully visualized many itch-mediating synaptic connections and neural networks in the spinal cord using "HVEM tomography". Moreover, the methodology used in this study is simple and can be applied in multiple ways. This is an important contribution to ultrastructural investigations of the central nervous system in the present post-genomic age.

Autonomic consequences of spinal cord injury

Spinal cord injury (SCI) results not only in motor and sensory deficits but also in autonomic dysfunctions. The disruption of connections between higher brain centers and the spinal cord, or the impaired autonomic nervous system itself, manifests a broad range of autonomic abnormalities. This includes compromised cardiovascular, respiratory, urinary, gastrointestinal, thermoregulatory, and sexual activities. These disabilities evoke potentially life-threatening symptoms that severely interfere with the daily living of those with SCI. In particular, high thoracic or cervical SCI often causes disordered hemodynamics due to deregulated sympathetic outflow. Episodic hypertension associated with autonomic dysreflexia develops as a result of massive sympathetic discharge often triggered by unpleasant visceral or sensory stimuli below the injury level. In the pelvic floor, bladder and urethral dysfunctions are classified according to upper motor neuron versus lower motor neuron injuries; this is dependent on the level of lesion. Most impairments of the lower urinary tract manifest in two interrelated complications: bladder storage and emptying. Inadequate or excessive detrusor and sphincter functions as well as detrusor-sphincter dyssynergia are examples of micturition abnormalities stemming from SCI. Gastrointestinal motility disorders in spinal cord injured-individuals are comprised of gastric dilation, delayed gastric emptying, and diminished propulsive transit along the entire gastrointestinal tract. As a critical consequence of SCI, neurogenic bowel dysfunction exhibits constipation and/or incontinence. Thus, it is essential to recognize neural mechanisms and pathophysiology underlying various complications of autonomic dysfunctions after SCI. This overview provides both vital information for better understanding these disorders and guides to pursue novel therapeutic approaches to alleviate secondary complications.

Activation of mu or delta opioid receptors in the lumbosacral spinal cord is essential for ejaculatory reflexes in male rats

Ejaculation is controlled by a spinal ejaculation generator located in the lumbosacral spinal cord, consisting in male rats of lumbar spinothalamic (LSt) cells and their inter-spinal projections to autonomic and motor centers. LSt cells co-express several neuropeptides, including gastrin releasing peptide (GRP) and enkephalin. We previously demonstrated in rats that GRP regulates ejaculation by acting within the lumbosacral spinal cord. In the present study, the hypothesis was tested that enkephalin controls ejaculation by acting on mu (MOR) or delta opioid receptors (DOR) in LSt target areas. Adult male rats were anesthetized and spinalized and received intrathecal infusions of vehicle, MOR antagonist CTOP (0.4 or 4 nmol), DOR antagonist (TIPP (0.4, 4 or 40 nmol), MOR agonist DAMGO (0.1 or 10 nmol), or DOR agonist deltorphin II (1.3 or 13 nmol). Ejaculatory reflexes were triggered by stimulation of the dorsal penile nerve (DPN) and seminal vesicle pressure and rhythmic contractions of the bulbocavernosus muscle were analyzed. Intrathecal infusion of MOR or DOR antagonists effectively blocked ejaculatory reflexes induced by DPN stimulation. Intrathecal infusion of DAMGO, but not deltorphin II triggered ejaculation in absence of DPN stimulation. Both MOR and DOR agonists facilitated ejaculatory reflexes induced by subthreshold DPN stimulation in all animals. Overall, these results support the hypothesis that enkephalin plays a critical role in the control of ejaculation in male rats. Activation of either MOR or DOR in LSt target areas is required for ejaculation, while MOR activation is sufficient to trigger ejaculation in the absence of sensory stimulation.

Distribution of gastrin-releasing peptide in the rat trigeminal and spinal somatosensory systems

Gastrin-releasing peptide (GRP) has recently been identified as an itch-specific neuropeptide in the spinal sensory system in mice, but there are no reports of the expression and distribution of GRP in the trigeminal sensory system in mammals. We characterized and compared GRP-immunoreactive (ir) neurons in the trigeminal ganglion (TG) with those in the rat spinal dorsal root ganglion (DRG). GRP immunoreactivity was expressed in 12% of TG and 6% of DRG neurons and was restricted to the small- and medium-sized type cells. In both the TG and DRG, many GRP-ir neurons also expressed substance P and calcitonin gene-related peptide, but not isolectin B4 . The different proportions of GRP and transient receptor potential vanilloid 1 double-positive neurons in the TG and DRG imply that itch sensations via the TG and DRG pathways are transmitted through distinct mechanisms. The distribution of the axon terminals of GRP-ir primary afferents and their synaptic connectivity with the rat trigeminal sensory nuclei and spinal dorsal horn were investigated by using light and electron microscopic histochemistry. Although GRP-ir fibers were rarely observed in the trigeminal sensory nucleus principalis, oralis, and interpolaris, they were predominant in the superficial layers of the trigeminal sensory nucleus caudalis (Vc), similar to the spinal dorsal horn. Ultrastructural analysis revealed that GRP-ir terminals contained clear microvesicles and large dense-cored vesicles, and formed asymmetric synaptic contacts with a few dendrites in the Vc and spinal dorsal horn. These results suggest that GRP-dependent orofacial and spinal pruriceptive inputs are processed mainly in the superficial laminae of the Vc and spinal dorsal horn.

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.

Sexually dimorphic nuclei in the spinal cord control male sexual functions

Lower spinal cord injuries frequently cause sexual dysfunction in men, including erectile dysfunction and an ejaculation disorder. This indicates that the important neural centers for male sexual function are located within the lower spinal cord. It is interesting that the lumbar spinal segments contain several neural circuits, showing a clear sexually dimorphism that, in association with neural circuits of the thoracic and sacral spinal cord, are critical in expressing penile reflexes during sexual behavior. To date, many sex differences in the spinal cord have been discovered. Interestingly, most of these are male dominant. Substantial evidence of sexually dimorphic neural circuits in the spinal cord have been reported in many animal models, but major issues remain unknown. For example, it is not known how the different circuits cooperatively function during male sexual behavior. In this review, therefore, the anatomical and functional significance of the sexually dimorphic nuclei in the spinal cord corresponding to the expression of male sexual behavior is discussed.

Intrinsic properties and neuropharmacology of midline paraventricular thalamic nucleus neurons

Neurons in the midline and intralaminar thalamic nuclei are components of an interconnected brainstem, limbic and prefrontal cortex neural network that is engaged during arousal, vigilance, motivated and addictive behaviors, and stress. To better understand the cellular mechanisms underlying these functions, here we review some of the recently characterized electrophysiological and neuropharmacological properties of neurons in the paraventricular thalamic nucleus (PVT), derived from whole cell patch clamp recordings in acute rat brain slice preparations. PVT neurons display firing patterns and ionic conductances (I_T and I_H) that exhibit significant diurnal change. Their resting membrane potential (RMP) is maintained by various ionic conductances that include inward rectifier (Kir), hyperpolarization-activated nonselective cation (HCN) and TWIK-related acid sensitive (TASK) K⁺ channels. Firing patterns are regulated by high voltage-activated (HVA) and low voltage-activated (LVA) Ca²⁺ conductances. Moreover, transient receptor potential (TRP)-like nonselective cation channels together with Ca²⁺- and Na⁺-activated K⁺ conductances (K_Ca; K_Na) contribute to unique slow afterhyperpolarizing potentials (sAHPs) that are generally not detectable in lateral thalamic or reticular thalamic nucleus neurons. The excitability of PVT neurons is also modulated by activation of neurotransmitter receptors associated with afferent pathways to PVT and other thalamic midline nuclei. We report on receptor-mediated actions of GABA, glutamate, monoamines and several neuropeptides: arginine vasopressin, gastrin-releasing peptide, thyrotropin releasing hormone and the orexins (hypocretins). This review represents an initial survey of intrinsic and transmitter-sensitive ionic conductances that are deemed to be unique to this population of midline thalamic neurons, information that is fundamental to an appreciation of the role these thalamic neurons may play in normal central nervous system (CNS) physiology and in CNS disorders that involve the dorsomedial thalamus.

Identification of CNS neurons innervating the levator ani and ventral bulbospongiosus muscles in male rats

INTRODUCTION

The pelvic striated muscles play an important role in mediating erections and ejaculation, and together these muscles compose a tightly coordinated neuromuscular system that is androgen sensitive and sexually dimorphic.

AIM

To identify spinal and brains neurons involved in the control of the levator ani (LA) and bulbospongiosus (BS) in the male adult and preadolescent rat.

METHODS

Rats were anesthetized, and the transsynaptic retrograde tracer pseudorabies virus (PRV) was injected into the LA muscle of adults or the ventral BS muscle in 30-day-old rats. After 3-5 days rats were sacrificed, and PRV-labeled neurons in the spinal cords and brains were identified using immunohistochemistry. The presence of gastrin-releasing peptide (GRP) in the lumbar spinal neurons was examined.

MAIN OUTCOMES MEASURES

The location and number of PRV-labeled neurons in the spinal cord and brain and GRP colocalization in the lumbar spinal cord.

RESULTS

PRV-labeled spinal interneurons were found distributed throughout T11-S1 of the spinal cord, subsequent to dorsal medial motoneuron infection. The majority of spinal interneurons were found in the lumbosacral spinal cord in the region of the dorsal gray commissure and parasympathetic preganglionic neurons. Preadolescent rats had more PRV-labeled spinal interneurons at L5-S1 where the motoneurons were located but relatively less spread rostrally in the spinal cord compared with adults. Lumbar spinothalmic neurons in medial gray of L3-L4 co-localized PRV and GRP. In the brain consistent labeling was seen in areas known to be involved in male sexual behavior including the ventrolateral medulla, hypothalamic paraventricular nucleus, and medial preoptic area.

CONCLUSION

Common spinal and brain pathways project to the LA and BS muscles in the rat suggesting that these muscles act together to coordinate male sexual reflexes. Differences may exist in the amount of synaptic connections/neuronal pathways in adolescents compared with adults.

Androgen regulates development of the sexually dimorphic gastrin-releasing peptide neuron system in the lumbar spinal cord: evidence from a mouse line lacking androgen receptor in the nervous system

Androgens including testosterone, organize the nervous system as well as masculine external and internal genitalia during the perinatal period. Androgen organization involves promotion of masculine body features, usually by acting through androgen receptors (ARs). We have recently demonstrated that the gastrin-releasing peptide (GRP) system in the lumbar spinal cord also mediates spinal centers promoting penile reflexes during male sexual behavior in rats. Testosterone may induce sexual differentiation of this spinal GRP system during development and maintain its activation in adulthood. In the present study, we examined the role of ARs in the nervous system regulating the development of the sexually dimorphic GRP system. For this purpose, we used a conditional mouse line selectively lacking the AR gene in the nervous system. AR floxed males carrying (mutants) or not (controls) the nestin-Cre transgene were castrated in adulthood and supplemented with physiological amounts of testosterone. Loss of AR expression in the nervous system resulted in a significant decrease in the number of GRP neurons compared to control littermates. Consequently, the intensity of GRP axonal projections onto the lower lumbar and upper sacral spinal cord was greater in control males than in mutant males. These results suggest that ARs expressed in the nervous system play a significant role in the development of the GRP system in the male lumbar spinal cord. The AR-deletion mutation may attenuate sexual behavior and activity of mutant males via spinal GRP system-mediated neural mechanisms.