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

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.

Footedness for scratching itchy eyes in rodents

The neural bases of itchy eye transmission remain unclear compared with those involved in body itch. Here, we show in rodents that the gastrin-releasing peptide receptor (GRPR) of the trigeminal sensory system is involved in the transmission of itchy eyes. Interestingly, we further demonstrate a difference in scratching behaviour between the left and right hindfeet in rodents; histamine instillation into the conjunctival sac of both eyes revealed right-foot biased laterality in the scratching movements. Unilateral histamine instillation specifically induced neural activation in the ipsilateral sensory pathway, with no significant difference between the activations following left- and right-eye instillations. Thus, the behavioural laterality is presumably due to right-foot preference in rodents. Genetically modified rats with specific depletion of Grpr-expressing neurons in the trigeminal sensory nucleus caudalis of the medulla oblongata exhibited fewer and shorter histamine-induced scratching movements than controls and eliminated the footedness. These results taken together indicate that the Grpr-expressing neurons are required for the transmission of itch sensation from the eyes, but that foot preference is generated centrally. These findings could open up a new field of research on the mechanisms of the laterality in vertebrates and also offer new potential therapeutic approaches to refractory pruritic eye disorders.

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.

Comparison of critical biomarkers in 2 erectile dysfunction models based on GEO and NOS-cGMP-PDE5 pathway

BACKGROUND

Erectile dysfunction is a disease commonly caused by diabetes mellitus (DMED) and cavernous nerve injury (CNIED). Bioinformatics analyses including differentially expressed genes (DEGs), enriched functions and pathways (EFPs), and protein-protein interaction (PPI) networks were carried out in DMED and CNIED rats in this study. The critical biomarkers that may intervene in nitric oxide synthase (NOS, predominantly nNOS, ancillary eNOS, and iNOS)-cyclic guanosine monophosphate (cGMP)-phosphodiesterase 5 enzyme (PDE5) pathway, an important mechanism in erectile dysfunction treatment, were then explored for potential clinical applications.

METHODS

GSE2457 and GSE31247 were downloaded. Their DEGs with a |logFC (fold change)| > 0 were screened out. Database for Annotation, Visualization and Integrated Discovery (DAVID) online database was used to analyze the EFPs in Gene Ontology enrichment and Kyoto Encyclopedia of Genes and Genomes networks based on down-regulated and up-regulated DEGs respectively. PPI analysis of 2 datasets was performed in Search Tool for the Retrieval of Interacting Genes/Proteins (STRING) and Cytoscape. Interactions with an average score greater than 0.9 were chosen as the cutoff for statistical significance.

RESULTS

From a total of 1710 DEGs in GSE2457, 772 were down-regulated and 938 were up-regulated, in contrast to the 836 DEGs in GSE31247, from which 508 were down-regulated and 328 were up-regulated. The 25 common EFPs such as aging and response to hormone were identified in both models. PPI results showed that the first 10 hub genes in DMED were all different from those in CNIED.

CONCLUSIONS

The intervention of iNOS with the hub gene complement component 3 in DMED and the aging process in both DMED and CNIED deserves attention.

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.

100 Hz Electroacupuncture Alleviated Chronic Itch and GRPR Expression Through Activation of Kappa Opioid Receptors in Spinal Dorsal Horn

Background

Clinical studies have shown that electroacupuncture (EA) alleviates chronic itch. Gastrin-releasing peptide receptor (GRPR) and dynorphin (DYN) in the spinal dorsal horn positively or negatively regulate itch, respectively. However, which frequency of EA is effective on relieving chronic itch and reducing the expression of GRPR, whether DYN-A in the spinal cord is involved in the underlying mechanism of the antipruritus effect of EA remains unknown.

Methods

The mixture of acetone and diethyl ether (1:1) [designated as AEW (acetone/diethyl ether and water) treatment] was used to induce the dry skin model of chronic itch. EA was applied to Quchi (LI11) and Hegu (LI4). Western blot was used to detect the expression of GRPR and DYN-A. Immunofluorescence was used to detect the expression of DYN-A.

Results

The AEW administration induced remarkable spontaneous scratching, enhanced the expression of GRPR, and reduced the expression of DYN-A. Compared with the sham EA, 2 Hz EA, or 15 Hz EA group, 100 Hz EA was the most effective frequency for relieving chronic itch, reducing the expression of GRPR, and increasing the expression of DYN-A in the cervical dorsal horn. Furthermore, intraperitoneal injection of kappa opioid receptors (KORs) antagonist nor-Binaltorphimine dihydrochloride (nor-BNI) significantly reversed the effect of 100 Hz EA on the inhibition of both itching behavior and GRPR expression.

Conclusion

EA at 100 Hz is the most effective frequency that inhibits chronic itch and GRPR expression through activation of KORs in the spinal dorsal horn, which can effectively guide the clinical treatment and improve the antipruritic effect of acupuncture.

Anti-inflammatory Effects of a Small Molecule Gastrin-Releasing Peptide Receptor Antagonist on Adjuvant-Induced Rheumatoid Arthritis in Rats

The anti-inflammatory effects of (R)-2-(1H-Imidazol-1-yl) ethyl-3-(1H-indol-3-yl)-2-(2-p-tolylacetamido)propanamide (RH-1402), a previous designed small molecule Gastrin releasing peptide (GRP) antagonist were evaluated in adjuvant-induced arthritic model of rats, and the inhibitory effect on neutrophil migration induced by GRP was determined by a transwell system experiment in vitro. The arthritis was induced by injection of Complete Freund's Adjuvant (CFA) containing 10 mg/mL of heat killed mycobacterium into the left hind footpad. Experimental rats were randomly divided into 6 groups, including control, placebo, positive control group, RH-1402 of low/middle/high dose group. Disease incidence and severity was evaluated through scoring of the paw edema and histologic features of joint synovial. Blood of all experimental rats was collected for interleukin 1β (IL-1β) and tumor necrosis factor α (TNF-α) cytokine levels. A transwell system was used to investigate whether RH-1402 would inhibit neutrophils migrating up a gradient of GRP in vitro. RH-1402 (5 and 10 mg/kg) significantly decreased adjuvant induced increased arthritis index during the administration period (days 14-20). Significant inhibition of joint synovial histological features can be found in the RH-1402 treated group, including alleviated Hyperplasia, Inflammatory of infiltration and activation of pannus formation. It also suppressed TNF-α and IL-1β level. Five and 10 mg/kg of RH-1402 significantly inhibited the effect of GRP on neutrophil migration with a dose dependent relationship. These findings indicate that RH-1402 have potential protective anti-inflammatory effects on experimental models of arthritis.

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).

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.

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.

Insights into bombesin receptors and ligands: Highlighting recent advances

This following article is written for Prof. Abba Kastin's Festschrift, to add to the tribute to his important role in the advancement of the role of peptides in physiological, as well as pathophysiological processes. There have been many advances during the 35 years of his prominent role in the Peptide field, not only as editor of the journal Peptides, but also as a scientific investigator and editor of two volumes of the Handbook of Biological Active Peptides [146,147]. Similar to the advances with many different peptides, during this 35 year period, there have been much progress made in the understanding of the pharmacology, cell biology and the role of (bombesin) Bn receptors and their ligands in various disease states, since the original isolation of bombesin from skin of the European frog Bombina bombina in 1970 [76]. This paper will briefly review some of these advances over the time period of Prof. Kastin 35 years in the peptide field concentrating on the advances since 2007 when many of the results from earlier studies were summarized [128,129]. It is appropriate to do this because there have been 280 articles published in Peptides during this time on bombesin-related peptides and it accounts for almost 5% of all publications. Furthermore, 22 Bn publications we have been involved in have been published in either Peptides [14,39,55,58,81,92,93,119,152,216,225,226,231,280,302,309,355,361,362] or in Prof. Kastin's Handbook of Biological Active Peptides [137,138,331].

Effective synaptome analysis of itch-mediating neurons in the spinal cord: A novel immunohistochemical methodology using high-voltage electron microscopy

Transmission electron microscopy (TEM) is used for three-dimensional (3-D) analysis of synaptic connections in neuroscience research. However, 3-D reconstruction of the synapses using serial ultrathin sections is a powerful but tedious approach requiring advanced technical skills. High-voltage electron microscopy (HVEM) allows examination of thicker sections of biological specimens due to the increased penetration of the more accelerated electrons, which is useful to analyze the 3-D structure of biological specimens. However, it is still difficult to visualize the neural networks and synaptic connections in 3-D using HVEM because of insufficient and non uniform heavy metal staining in the membranous structures in semi-thin sections. Here, we present the successful chemical 3-D neuroanatomy of the rat spinal dorsal horn at the ultrastructural level as a first step for effective synaptome analysis by applying a high-contrast en bloc staining method to immune-HVEM tomography. Our new approach made it possible to examine many itch-mediating synaptic connections and neural networks in the spinal cord simultaneously using HVEM tomography. This novel 3-D electron microscopy is very useful for the analysis of synaptic structure and the chemical neuroanatomy at the 3-D ultrastructural level.