Pathophysiological and therapeutic implications of neuropeptide S system in neurological disorders

Neuropeptide S (NPS) is a 20 amino acids-containing neuroactive molecule discovered by the reverse pharmacology method. NPS is detected in specific brain regions like the brainstem, amygdala, and hypothalamus, while its receptor (NPSR) is ubiquitously expressed in the central nervous system (CNS). Besides CNS, NPS and NPSR are also expressed in the peripheral nervous system. NPSR is a G-protein coupled receptor that primarily uses Gq and Gs signaling pathways to mediate the actions of NPS. In animal models of Parkinsonism and Alzheimer's disease, NPS exerts neuroprotective effects. NPS suppresses oxidative stress, anxiety, food intake, and pain, and promotes arousal. NPSR facilitates reward, reinforcement, and addiction-related behaviors. Genetic variation and single nucleotide polymorphism in NPSR are associated with depression, schizophrenia, rheumatoid arthritis, and asthma. NPS interacts with several neurotransmitters including glutamate, noradrenaline, serotonin, corticotropin-releasing factor, and gamma-aminobutyric acid. It also modulates the immune system via augmenting pro-inflammatory cytokines and plays an important role in the pathogenesis of rheumatoid arthritis and asthma. In the present review, we discussed the distribution profile of NPS and NPSR, signaling pathways, and their importance in the pathophysiology of various neurological disorders. We have also proposed the areas where further investigations on the NPS system are warranted.

Neuropeptide S Receptor 1 variant (I107N) regulates behavioral characteristics and NPS effect in mice in a sex-dependent manner

Accumulated data demonstrate that the A/T single-nucleotide polymorphism (SNP) rs324981 in the human neuropeptide S receptor 1 (NPSR1) gene, resulting in an amino acid change from asparagine (N) to isoleucine (I) at position 107, is associated with susceptibility to psychiatric disorders. Neuropeptide S (NPS) has also been implicated in modulating these disorders in rodent experiments. However, the effect of this SNP on NPSR1 activity remains unclear. To elucidate the pathophysiological and pharmacological implications of this SNP, we generated a mouse model carrying the human-specific AA variant in NPSR1. This model exhibited sex-specific behavioral differences mirroring human observations, including fear response, anxiety, and depression. Notably, intracerebroventricular administration of NPS (1 nmol) significantly promoted locomotor activity and alleviated looming-stimulated fear and anxiety-like behaviors in NPSR TT mice, but not in NPSR AA mice. NPS also reduced depression-like behavior in a sex and genotype-dependent manner in the forced swim test. Our study in NPSR variant mice enhances our understanding of phenotypic and pharmacological differences due to the NPSR1 SNP, providing an animal model for further investigation of physiological processes in humans carrying this SNP.

RTI-263, a biased neuropeptide S receptor agonist that retains an anxiolytic effect, attenuates cocaine-seeking behavior in rats

Neuropeptide S (NPS) is a neuromodulatory peptide that acts via a G protein-coupled receptor. Centrally administered NPS suppresses anxiety-like behaviors in rodents while producing a paradoxical increase in arousal. In addition, NPS increases drug-seeking behavior when administered during cue-induced reinstatement. Conversely, an NPS receptor (NPSR) antagonist, RTI-118, decreases cocaine-seeking behavior. A biased NPSR ligand, RTI-263, produces anxiolytic-like effects and has memory-enhancing effects similar to those of NPS but without the increase in arousal. In the present study, we show that RTI-263 decreased cocaine seeking by both male and female rats during cue-induced reinstatement. However, RTI-263 did not modulate the animals' behaviors during natural reward paradigms, such as palatable food intake, feeding during a fasting state, and cue-induced reinstatement of sucrose seeking. Therefore, NPSR biased agonists are a potential pharmacotherapy for substance use disorder because of the combined benefits of decreased drug seeking and the suppression of anxiety.

Neuropeptide S promotes maintenance of newly formed dendritic spines and performance improvement after motor learning in mice

Neuropeptide S (NPS), an endogenous neuropeptide consisting of 20 amino acids, selectively binds and activates G protein-coupled receptor named neuropeptide S receptor (NPSR) to regulate a variety of physiological functions. NPS/NPSR system has been shown to play a pivotal role in regulating learning and memory in rodents. However, it remains unclear that how NPS/NPSR system affects neuronal functions and synaptic plasticity after learning. We found that intracerebroventricular (i.c.v.) injection of NPS promoted performance improvement and reduced sleep duration after motor learning, which could be blocked by pre-treatment with intraperitoneal (i.p.) injection of NPSR antagonist SHA 68. Using intravital two-photon imaging, we examined the effect of NPS on the postsynaptic dendritic spines of layer V pyramidal neurons in the mouse primary motor cortex after motor learning. We found that i.c.v. injection of NPS strengthened learning-induce new spines and facilitated their survival over time. Furthermore, i.c.v. injection of NPS increased calcium activity of apical dendrites and dendritic spines of layer V pyramidal neurons in the mouse primary motor cortex during the running period. These findings suggest that activation of NPSR by NPS increases synaptic calcium activity and learning-related synapse maintenance, thereby contributing to performance improvement after motor learning.

Neuropeptide S and its receptor NPSR enhance the susceptibility of hosts to pseudorabies virus infection

The neuropeptide S (NPS) and its receptor (NPSR) represent a signaling system in the brain. Increased levels of NPS and NPSR have been observed in PK15 cells and murine brains in response to pseudorabies virus (PRV) infection, but it remains unclear whether elevated levels of NPS and NPSR are involved in the pathogenic process of PRV infection. In this study, the activities of both NPS and NPSR during PRV pathogenesis were explored in vitro and in vivo by reverse transcription polymerase chain reaction (RT-PCR), PCR, real-time quantitative RT-PCR (qRT-PCR), qPCR, TCID50, and Western blotting methods. NPSR-deficient cells were less susceptible to PRV infection, as evidenced by decreased viral production and PRV-glycoprotein E (gE) expression. In vitro studies showed that exogenous NPS promoted the expression of interleukin 6 (IL-6) mRNA but inhibited interferon β (IFN-β) mRNA expression in PK15 cells after PRV infection. In vivo studies showed that NPS-treated mice were highly susceptible to PRV infection, with decreased survival rates and body weights. In addition, NPS-treated mice showed elevated levels of IL-6 mRNA and STAT3 phosphorylation. However, the expression of IFN-β mRNA was greatly decreased after virus challenge. Contrasting results were obtained from the NPSR-ir-treated groups, which further highlighted the effects of NPS. This study revealed that NPS-treated hosts are more susceptible to PRV infection than controls. Moreover, excessive IL-6/STAT3 and defective IFN-β responses in NPS-treated mice may contribute to the pathogenesis of PRV.

Modulatory effect of long-term treatment with escitalopram and clonazepam on the expression of anxiety-related neuropeptides: neuromedin U, neuropeptide S and their receptors in the rat brain

BACKGROUND

Newly identified multifunctional peptidergic modulators of stress responses: neuromedin U (NMU) and neuropeptide S (NPS) are involved in the wide spectrum of brain functions. However, there are no reports dealing with potential molecular relationships between the action of diverse anxiolytic or antidepressant drugs and NMU and NPS signaling in the brain. The present work was therefore focused on local expression of the aforementioned stress-related neuropeptides in the rat brain after long-term treatment with escitalopram and clonazepam.

METHODS

Studies were carried out on adult, male Sprague-Dawley rats that were divided into 3 groups: animals injected with saline (control) and experimental individuals treated with escitalopram (at single dose 5 mg/kg daily), and clonazepam (at single dose 0.5 mg/kg). All individuals were sacrificed under anaesthesia and the whole brain excised. Total mRNA was isolated from homogenized samples of amygdala, hippocampus, hypothalamus, thalamus, cerebellum and brainstem. Real time-PCR method was used for estimation of related NPS, NPS receptor (NPSR), NMU, NMU and receptor 2 (NMUR2) mRNA expression. The whole brains were also sliced for general immunohistochemical assessment of the neuropeptides expression.

RESULTS

Chronic administration of clonazepam resulted in an increase of NMU mRNA expression and formation of NMU-expressing fibers in the amygdala, while escitalopram produced a significant decrease in NPSR mRNA level in hypothalamus. Long-term escitalopram administration affects the local expression of examined neuropeptides mRNA in a varied manner depending on the brain structure.

CONCLUSIONS

Pharmacological effects of escitalopram may be connected with local at least partially NPSR-related alterations in the NPS/NMU/NMUR2 gene expression at the level selected rat brain regions. A novel alternative mode of SSRI action can be therefore cautiously proposed.

Escitalopram alters local expression of noncanonical stress-related neuropeptides in the rat brain via NPS receptor signaling

BACKGROUND

Neuropeptide S (NPS) is a multifunctional regulatory factor that exhibits a potent anxiolytic activity in animal models. However, there are no reports dealing with the potential molecular relationships between the anxiolytic activity of selective serotonin reuptake inhibitors (SSRIs) and NPS signaling, especially in the context of novel stress-related neuropeptides action. The present work therefore focused on gene expression of novel stress neuropeptides in the rat brain after acute treatment with escitalopram and in combination with neuropeptide S receptor (NPSR) blockade.

METHODS

Studies were carried out on adult, male Sprague-Dawley rats that were divided into five groups: animals injected with saline (control) and experimental rats treated with escitalopram (at single dose 10 mg/kg daily), escitalopram and SHA-68, a selective NPSR antagonist (at a single dose of 40 mg/kg), SHA-68 alone and corresponding vehicle (solvent SHA-68) control. To measure anxiety-like behavior and locomotor activity the open field test was performed. All individuals were killed under anaesthesia and the whole brain was excised. Total mRNA was isolated from homogenized samples of the amygdala, hippocampus, hypothalamus, thalamus, cerebellum, and brainstem. Real-time PCR was used for estimation of related NPS, NPSR, neuromedin U (NMU), NMU receptor 2 (NMUR2) and nesfatin-1 precursor nucleobindin-2 (NUCB2) gene expression.

RESULTS

Acute escitalopram administration affects the local expression of the examined neuropeptides mRNA in a varied manner depending on brain location. An increase in NPSR and NUCB2 mRNA expression in the hypothalamus and brainstem was abolished by SHA-68 coadministration, while NMU mRNA expression was upregulated after NPSR blockade in the hippocampus and cerebellum.

CONCLUSIONS

The pharmacological effects of escitalopram may be connected with local NPSR-related alterations in NPS/NMU/NMUR2 and nesfatin-1 gene expression at the level of selected rat brain regions. A novel alternative mode of SSRI action can be therefore cautiously proposed.

Human-Specific Neuropeptide S Receptor Variants Regulate Fear Extinction in the Basal Amygdala of Male and Female Mice Depending on Threat Salience

BACKGROUND

A nonsynonymous single nucleotide polymorphism in the neuropeptide S receptor 1 (NPSR1) gene (rs324981) results in isoleucine-to-asparagine substitution at amino acid 107. In humans, the ancestral variant (NPSR1 I107) is associated with increased anxiety sensitivity and risk of panic disorder, while the human-specific variant (NPSR1 N107) is considered protective against excessive anxiety. In rodents, neurobiological constituents of the NPS system have been analyzed in detail and their anxiolytic-like effects have been endorsed. However, their implication for anxiety and related disorders in humans remains unclear, as rodents carry only the ancestral NPSR1 I107 variant.

METHODS

We hypothesized that phenotypic correlates of NPSR1 variants manifest in fear-related circuits in the amygdala. We used CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats/Cas9)-mediated gene editing to generate a "humanized" mouse strain, in which individuals express either NPSR1 I107 or NPSR1 N107.

RESULTS

Stimulation of NPSR1 evoked excitatory responses in principal neurons of the anterior basal amygdala with significant differences in magnitude between genotypes, resulting in synaptic disinhibition of putative extinction neurons in the posterior basal amygdala in mice expressing the human-specific hypofunctional N107 but not the ancestral I107 variant. N107 mice displayed improved extinction of conditioned fear, which was phenocopied after pharmacological antagonism of NPSR1 in the anterior basal amygdala of I107 mice. Differences in fear extinction between male and female mice were related to an interaction of Npsr1 genotype and salience of fear training.

CONCLUSIONS

The NPS system regulates extinction circuits in the amygdala depending on the Npsr1 genotype, contributing to sex-specific differences in fear extinction and high anxiety sensitivity of individuals bearing the ancestral NPSR1 I107 variant.

Roles of Neuropeptide S in Anesthesia, Analgesia, and Sleep

Neuropeptide S (NPS) is an endogenous peptide that regulates various physiological functions, such as immune functions, anxiety-like behaviors, learning and memory, the sleep–wake rhythm, ingestion, energy balance, and drug addiction. These processes include the NPS receptor (NPSR1). The NPS–NPSR1 system is also significantly associated with the onset of disease, as well as these physiologic functions. For example, NPS is involved in bronchial asthma, anxiety and awakening disorders, and rheumatoid arthritis. In this review, among the various functions, we focus on the role of NPS in anesthesia-induced loss of consciousness; analgesia, mainly by anesthesia; and sleep–wakefulness. Progress in the field regarding the functions of endogenous peptides in the brain, including NPS, suggests that these three domains share common mechanisms. Further NPS research will help to elucidate in detail how these three domains interact with each other in their functions, and may contribute to improving the quality of medical care.

Hypothalamic stress systems in mood disorders

Stress system dysfunction is a typical characteristic of acute depression and other mood disorders. The exact pattern of factors predisposing for stress-related mental disorders is yet to be unraveled. However, corticosteroid receptor function plays an important role for appropriate or dysfunctional neuroendocrine responses to stress exposure and hence in resilience or risk for the development and course of both, depression and anxiety disorders. Solid neuroscience data strongly support that both neuropeptides, corticotropin-releasing hormone (CRH) and vasopressin (AVP), are central in coordinating humoral and behavioral adaptation to stress. Other neuropeptides, including oxytocin, neuropeptide S, neuropeptide Y, and orexin, are also considered important contributors. Attempts to turn neuropeptide biology into treatments for stress-related disorders need to consider that neuropeptide receptors are specific drug targets for certain patient populations rather than universal targets for all patients, like biogenic amine systems. That is why most negative clinical trials testing neuropeptide receptor antagonists have been in fact failed trials by design, because no companion tests were used to identify which patients with depression are most likely to benefit from a specific neuropeptide receptor-targeting drug treatment. Therefore, the most important future research task is discovery and development of appropriate companion tests that will allow the successful transfer of the precious treasure of neuropeptide system-targeting drugs into clinics.

The hypothalamic mechanism of neuropeptide S-induced satiety in Japanese quail (Coturnix japonica) involves the paraventricular nucleus and corticotropin-releasing factor

Neuropeptide S (NPS), a 20-amino acid neuropeptide, is produced in the brain and is associated with appetite suppression.Our group was the first to report this anorexigenic effect in birds using chicken as a model, although a hypothalamic molecular mechanism remains to be elucidated. Thus, we designed the present study using Japanese quail(Coturnix japonica).In Experiment 1, quail intracerebroventricularly injected with NPS reduced both food and water intake. In Experiment 2, food-restricted quail injected with NPS displayed a reduction in water intake.In Experiment 3, NPS-injected quail reduced their feeding and exploratory pecks.In Experiment 4, we quantified the number of cells expressing the early intermediate gene product c-Fos (as a marker of neuronal activation) in appetite associated hypothalamic nuclei and found that immunoreactivity was increased in the paraventricular nucleus (PVN). In Experiment 5, we utilized real-time PCR to screen for neuropeptide changes within the PVN of NPS-injected quail. Mesotocin and corticotropin-releasing factor (CRF) mRNAs increased in response to NPS injection. In Experiment 6, co-injection of astressin, a CRF receptor antagonist, was sufficient to block the food intake-suppressive effects of NPS, but in Experiment 7, co-injection of an oxytocin receptor antagonist was not sufficient to block the food intake-suppressive effects of NPS. Collectively, results support that NPS induces an anorexigenic response in Japanese quail that is mediated within the PVN and is associated with CRF.

Neuropeptide S-initiated sequential cascade mediated by OX1, NK1, mGlu5 and CB1 receptors: a pivotal role in stress-induced analgesia

Background

Stress-induced analgesia (SIA) is an evolutionarily conserved phenomenon during stress. Neuropeptide S (NPS), orexins, substance P, glutamate and endocannabinoids are known to be involved in stress and/or SIA, however their causal links remain unclear. Here, we reveal an unprecedented sequential cascade involving these mediators in the lateral hypothalamus (LH) and ventrolateral periaqueductal gray (vlPAG) using a restraint stress-induced SIA model.

Methods

Male C57BL/6 mice of 8–12 week-old were subjected to intra-cerebroventricular (i.c.v.) and/or intra-vlPAG (i.pag.) microinjection of NPS, orexin-A or substance P alone or in combination with selective antagonists of NPS receptors (NPSRs), OX₁ receptors (OX₁Rs), NK₁ receptors (NK₁Rs), mGlu₅ receptors (mGlu₅Rs) and CB₁ receptors (CB₁Rs), respectively. Antinociceptive effects of these mediators were evaluated via the hot-plate test. SIA in mice was induced by a 30-min restraint stress. NPS levels in the LH and substance P levels in vlPAG homogenates were compared in restrained and unrestrained mice.

Results

NPS (i.c.v., but not i.pag.) induced antinociception. This effect was prevented by i.c.v. blockade of NPSRs. Substance P (i.pag.) and orexin-A (i.pag.) also induced antinociception. Substance P (i.pag.)-induced antinociception was prevented by i.pag. Blockade of NK₁Rs, mGlu₅Rs or CB₁Rs. Orexin-A (i.pag.)-induced antinociception has been shown previously to be prevented by i.pag. blockade of OX₁Rs or CB₁Rs, and here was prevented by NK₁R or mGlu₅R antagonist (i.pag.). NPS (i.c.v.)-induced antinociception was prevented by i.pag. blockade of OX₁Rs, NK₁Rs, mGlu₅Rs or CB₁Rs. SIA has been previously shown to be prevented by i.pag. blockade of OX₁Rs or CB₁Rs. Here, we found that SIA was also prevented by i.c.v. blockade of NPSRs or i.pag. blockade of NK₁Rs or mGlu₅Rs. Restrained mice had higher levels of NPS in the LH and substance P in the vlPAG than unrestrained mice.

Conclusions

These results suggest that, during stress, NPS is released and activates LH orexin neurons via NPSRs, releasing orexins in the vlPAG. Orexins then activate OX₁Rs on substance P-containing neurons in the vlPAG to release substance P that subsequently. Activates NK₁Rs on glutamatergic neurons to release glutamate. Glutamate then activates perisynaptic mGlu₅Rs to initiate the endocannabinoid retrograde inhibition of GABAergic transmission in the vlPAG, leading to analgesia.

Dopamine D1 and D2 receptors mediate neuropeptide S-induced antinociception in the mouse formalin test

Neuropeptide S (NPS) is the endogenous ligand of a G-protein coupled receptor named NPS receptor. The NPS system controls several biological functions, including anxiety, wakefulness, locomotor activity, food intake, and pain transmission. A growing body of evidence supports facilitatory effects for NPS over dopaminergic neurotransmission. The present study was aimed to investigate the role of dopamine receptors signaling in the antinociceptive effects of NPS in the mouse formalin test. The following dopamine receptor antagonists were employed: SCH 23390 (selective dopamine D₁ antagonist, 0.05 mg/kg, ip), haloperidol (non-selective dopamine D₂-like receptor antagonist; 0.03 mg/kg, ip), and sulpiride (selective dopamine D₂-like receptor antagonist; 25 mg/kg, ip). Mice were pretreated with dopamine antagonists before the supraspinal administration of NPS (0.1 nmol, icv). Morphine (5 mg/kg, sc) and indomethacin (10 mg/kg, ip) were used as positive controls to set up the experimental conditions. Morphine-induced antinociceptive effects were observed during phases 1 and 2 of the test, while indomethacin was only active at phase 2. Central NPS significantly reduced formalin-induced nociception during both phases. The systemic administration of SCH 23390 slightly blocked the effects of NPS only during phase 2. Haloperidol prevented NPS-induced antinociceptive effects. Similar to haloperidol, sulpiride also counteracted the antinociceptive effects of NPS in both phases of the formalin test. In conclusion, the present findings suggest that the analgesic effects of NPS are linked with dopaminergic neurotransmission mainly through dopamine D₂-like receptor signaling.

Neuropeptide S Ameliorates Cognitive Impairment of APP/PS1 Transgenic Mice by Promoting Synaptic Plasticity and Reducing Aβ Deposition

Alzheimer’s disease (AD) is a devastating disease in the elderly with no known effective treatment. It is characterized by progressive deterioration of memory and cognition. Many new potential targets are being investigated to develop effective therapeutic strategies for AD. Neuropeptide S (NPS) is an endogenous peptide in the central nervous system, which has been shown to play a beneficial role in learning and memory. However, whether NPS can ameliorate cognitive deficits in AD remains unclear. In this study, we examined the effects of NPS treatment on the cognitive behaviors and pathological hallmarks in 8-month-old APPswe/PS1dE9 (APP/PS1) AD mice. We found that the APP/PS1 mice exhibited lower levels of NPS receptors (NPSRs) in the hippocampal area, and NPS administration increased c-Fos expression in the hippocampus and cortex, which suggests the NPS/NPSR system may contribute to the pathogenesis of AD. After an intracerebroventricular injection of NPS (1 nmol) for 2 weeks, we found NPS treatment ameliorated spatial memory deficits and promoted dendrite ramification and spine generation in hippocampal CA1 neurons, which was accompanied by the upregulation of postsynaptic density protein 95 (PSD95) and synapsin1. We also demonstrated that the injection of NPS decreased Aβ plaque deposits by decreasing the γ-secretase activity and the phosphorylation of APP at Thr668. Furthermore, application of NPS reversed the deficits in hippocampal late-phase long-term potentiation (LTP). These findings suggest NPS attenuated cognitive deficits by reducing pathological features in APP/PS1 mice, and NPS might be a potential therapeutic agent for AD.

Sustained overexpression of neuropeptide S in the amygdala reduces anxiety-like behavior in rats

Neuropeptide S (NPS) has shown anxiolytic-like effects in rodents after acute administration, but its long-term effects remain unknown. Gene therapy enables the targeted delivery of DNA to cell nuclei, and recombinant adeno-associated viral (rAAV) vectors have been identified as suitable tools for stable overexpression. Thus, to explore the effects of long-term expression of NPS, the present study examined anxiety- and depressive-like effects after rAAV-mediated NPS overexpression in the rat amygdala. Compared to rats injected with an empty control vector (rAAV-Empty), rAAV-NPS treatment was associated with reduced anxiety-like behavior in the elevated plus maze and light-dark box, but did not affect depressive-like behavior in the forced swim test. Importantly, rAAV-NPS did not cause confounding effects on locomotion or bodyweight as opposed to currently used anxiolytic drugs. Immunohistochemical stainings revealed NPS-positive cells in the central and basolateral region of the amygdala in rAAV-NPS but not rAAV-Empty rats, indicating successful transduction. Our study provides novel evidence for sustained anxiolytic-like properties of NPS by transgenic overexpression. These data suggest that rAAV-NPS application deserves further attention as a potential treatment strategy for anxiety in humans.

Physiology, pharmacology, and pathophysiology of neuropeptide S receptor

Neuropeptide S receptor 1 (NPSR1), originally named G protein-coupled receptor 154 (GPR154), was deorphanized in 2002 with neuropeptide S identified as the endogenous ligand. NPSR1 is primarily expressed in bronchus, brain as well as immune cells. It regulates multiple physiological processes, including immunoregulation, locomotor activity, anxiety, arousal, learning and memory, and food intake and energy balance. SNPs of NPSR1 are significantly associated with several diseases, including asthma, anxiolytic and arousal disorders, and rheumatoid arthritis. This chapter will summarize studies on NPSR1, including its molecular structure, tissue distribution, physiology, pharmacology, and pathophysiology.

Small Molecule Neuropeptide S and Melanocortin 4 Receptor Ligands as Potential Treatments for Substance Use Disorders

There is a vital need for novel approaches and biological targets for drug discovery and development. Treatment strategies for substance use disorders (SUDs) to date have been mostly ineffective other than substitution-like therapeutics. Two such targets are the peptide G-protein-coupled receptors neuropeptide S (NPS) and melanocortin 4 (MC4). Preclinical evidence suggests that antagonists, inverse agonists, or negative allosteric modulators of these receptors might be novel therapeutics for SUDs. NPS is a relatively unexplored receptor with high potential for treating SUD. MC4 has a strong link to early-onset obesity, and emerging evidence suggests significant overlap between food-maintained and drug-maintained behaviors making MC4 an intriguing target for SUD. This chapter provides an overview of the literature in relation to the roles of NPS and MC4 in drug-seeking behaviors and then provides a medicinal chemistry-based survey of the small molecule ligands for each receptor.

Brain neuropeptide S: via GPCR activation to a powerful neuromodulator of socio-emotional behaviors

Neuropeptide S (NPS) has attracted the attention of the scientific community due to its potent anxiolytic-like and fear-attenuating effects studied in rodents. Therefore, NPS might represent a treatment option for neuropsychiatric disorders, such as anxiety disorders, even more so as single nucleotide polymorphisms in the human NPS receptor gene have been associated with increased anxiety traits that contribute to the pathogenesis of fear- and anxiety-related disorders. However, the signaling mechanisms underlying the behavioral effects of NPS and the interaction with other brain neuropeptides are still rather unknown. To illuminate how NPS modulates the expression of selected emotional and social behaviors, the present review focuses on neuroanatomical and electrophysiological studies, as well as intracellular signaling mechanisms following NPS receptor stimulation in rodents. We will also discuss interactions of the NPS system with two well-described neuropeptides, namely corticotropin-releasing factor and oxytocin, which may contribute to the fear- and anxiety-reducing effects.

Neuropeptide S in the basolateral amygdala mediates an adaptive behavioral stress response in a rat model of posttraumatic stress disorder by increasing the expression of BDNF and the neuropeptide YY1 receptor

Neuropeptide S (NPS) is a regulatory peptide that has anxiolytic and arousal-promoting effects in rodents. We used an animal model of posttraumatic stress disorder (PTSD) to assess long-term behavioral effects of a single dose of NPS, microinjected into the basolateral amygdala (BLA) 1h following exposure to predator-scent stress (PSS). To elucidate the molecular mechanism by which NPS attenuates behavioral stress responses, expression levels of neuropeptide Y (NPY), NPY-Y1 receptor (NPY-Y1R), and brain-derived neurotrophic factor (BDNF) were evaluated in the hippocampus. The behavioral and molecular effects of NPS receptor antagonist (NPS-RA), NPY-Y1R antagonist (NPY-Y1RA), or both administered centrally were evaluated in the same manner. Circulating corticosterone levels were measured at different time points following PSS-exposure. Immediate post-exposure treatment with NPS had a marked protective effect; BLA microinfusion of NPS completely abolished the extreme behavioral response to PSS, restored the decreased expression of BDNF and, unexpectedly, PY-Y1R, but didn't affect the decreased expression of NPY. BLA microinfusion of both NPY-Y1RA and NPS-RA together had an additive effect, which completely prevented the anxiolytic effects of NPS in rats exposed to PSS and disrupted the expression of NPY-Y1R in the hippocampus following NPS infusion. It may therefore be hypothesized that NPS acts, directly or indirectly, on both the NPY-Y1R and NPS receptors and that the cross-talk between NPS and NPY-Y1R may be necessary for the anxiolytic effects of NPS post-exposure. The NPS system might thus contribute to a potential endogenous mechanism underlying the shift towards adaptive behavioral response and thereby might be relevant as a pharmacological target for attenuating stress-related sequelae.

Peptide welding technology - A simple strategy for generating innovative ligands for G protein coupled receptors

Based on their high selectivity of action and low toxicity, naturally occurring peptides have great potential in terms of drug development. However, the pharmacokinetic properties of peptides, in particular their half life, are poor. Among different strategies developed for reducing susceptibility to peptidases, and thus increasing the duration of action of peptides, the generation of branched peptides has been described. However, the synthesis and purification of branched peptides are extremely complicated thus limiting their druggability. Here we present a novel and facile synthesis of tetrabranched peptides acting as GPCR ligands and their in vitro and vivo pharmacological characterization. Tetrabranched derivatives of nociceptin/orphanin FQ (N/OFQ), N/OFQ related peptides, opioid peptides, tachykinins, and neuropeptide S were generated with the strategy named peptide welding technology (PWT) and characterized by high yield and purity of the desired final product. In general, PWT derivatives displayed a pharmacological profile similar to that of the natural sequence in terms of affinity, pharmacological activity, potency, and selectivity of action in vitro. More importantly, in vivo studies demonstrated that PWT peptides are characterized by increased potency associated with long lasting duration of action. In conclusion, PWT derivatives of biologically active peptides can be viewed as innovative pharmacological tools for investigating those conditions and states in which selective and prolonged receptor stimulation promotes beneficial effects.

Neuropeptide S overcomes short term memory deficit induced by sleep restriction by increasing prefrontal cortex activity

Sleep restriction (SR) impairs short term memory (STM) that might be related to different processes. Neuropeptide S (NPS), an endogenous neuropeptide that improves short term memory, activates arousal and decreases anxiety is likely to counteract the SR-induced impairment of STM. The objective of the present study was to find common cerebral pathways in sleep restriction and NPS action in order to ultimately antagonize SR effect on memory. The STM was assessed using a spontaneous spatial alternation task in a T-maze. C57-Bl/6J male mice were distributed in 4 groups according to treatment (0.1nmol of NPS or vehicle intracerebroventricular injection) and to 20h-SR. Immediately after behavioural testing, regional c-fos immunohistochemistry was performed and used as a neural activation marker for spatial short term memory (prefrontal cortex, dorsal hippocampus) and emotional reactivity (basolateral amygdala and ventral hippocampus). Anxiety-like behaviour was assessed using elevated-plus maze task. Results showed that SR impaired short term memory performance and decreased neuronal activation in cingular cortex.NPS injection overcame SR-induced STM deficits and increased neuronal activation in infralimbic cortex. SR spared anxiety-like behavior in the elevated-plus maze. Neural activation in basolateral nucleus of amygdala and ventral hippocampus were not changed after SR.In conclusion, the present study shows that NPS overcomes SR-induced STM deficits by increasing prefrontal cortex activation independently of anxiety-like behaviour.

Central noradrenergic activity affects analgesic effect of Neuropeptide S

BACKGROUND

Neuropeptide S (NPS) is an endogenous neuropeptide controlling anxiolysis, wakefulness, and analgesia. NPS containing neurons exist near to the locus coeruleus (LC) involved in the descending anti-nociceptive system. NPS interacts with central noradrenergic neurons; thus brain noradrenergic signaling may be involved in NPS-induced analgesia. We tested NPS analgesia in noradrenergic neuron-lesioned rats using a selective LC noradrenergic neurotoxin, N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4).

METHODS

A total 66 male Sprague-Dawley rats weighing 350-450 g were used. Analgesic effects of NPS were evaluated using hot-plate and tail-flick test with or without DSP-4. The animal allocated into 3 groups; hot-plate with NPS alone intracerebroventricular (icv) (0.0, 1.0, 3.3, and 10.0 nmol), tail-flick NPS alone icv (0.0 and 10.0 nmol), and hot-plate with NPS and DSP-4 (0 or 50 mg/kg ip). In hot-plate with NPS and DSP-4 group, noradrenaline content in the cerebral cortex, pons, hypothalamus, were measured.

RESULTS

NPS 10 nmol icv prolonged hot plate (%MPE) but not tail flick latency at 30 and 40 min after administration. DSP-4 50 mg/kg decreased noradrenaline content in the all 3 regions. The NA depletion inhibited NPS analgesic effect in the hot plate test but not tail flick test. There was a significant correlation between hot plate latency (percentage of maximum possible effect: %MPE) with NPS 10 nmol and NA content in the cerebral cortex (p = 0.017, r ² = 0.346) which noradrenergic innervation arisen mainly from the LC. No other regions had the correlation.

CONCLUSIONS

NPS analgesia interacts with LC noradrenergic neuronal activity.

Neuropeptide S increases motor activity and thermogenesis in the rat through sympathetic activation

The central role of neuropeptide S (NPS), identified as the endogenous ligand for GPR154, now named neuropeptide S receptor (NPSR), has not yet been fully clarified. We examined the central role of NPS for body temperature, energy expenditure, locomotor activity and adrenal hormone secretion in rats. Intracerebroventricular (icv) injection of NPS increased body temperature in a dose-dependent manner. Energy consumption and locomotor activity were also significantly increased by icv injection of NPS. In addition, icv injection of NPS increased the peripheral blood concentration of adrenalin and corticosterone. Pretreatment with the β1- and β2-adrenergic receptor blocker timolol inhibited the NPS-induced increase of body temperature. The expression of both NPS mRNA in the brainstem and NPSR mRNA in the hypothalamus showed a nocturnal rhythm with a peak occurring during the first half of the dark period. To examine whether the endogenous NPS is involved in regulation of body temperature, NPSR antagonist SHA68 was administered one hour after darkness. SHA68 attenuated the nocturnal rise of body temperature. These results suggest that NPS contributes to the regulation of the sympathetic nervous system.

Identification of the first biased NPS receptor agonist that retains anxiolytic and memory promoting effects with reduced levels of locomotor stimulation

The neuropeptide S system has been implicated in a number of centrally mediated behaviors including memory consolidation, anxiolysis, and increased locomotor activity. Characterization of these behaviors has been primarily accomplished using the endogenous 20AA peptide (NPS) that demonstrates relatively equal potency for the calcium mobilization and cAMP second messenger pathways at human and rodent NPS receptors. This study is the first to demonstrate that truncations of the NPS peptide provides small fragments that retain significant potency only at one of two single polymorphism variants known to alter NPSR function (NPSR-107I), yet demonstrate a strong level of bias for the calcium mobilization pathway over the cAMP pathway. We have also determined that the length of the truncated peptide correlates with the degree of bias for the calcium mobilization pathway. A modified tetrapeptide analog (4) has greatly attenuated hyperlocomotor stimulation in vivo but retains activity in assays that correlate with memory consolidation and anxiolytic activity. Analog 4 also has a bias for the calcium mobilization pathway, at the human and mouse receptor. This suggests that future agonist ligands for the NPS receptor having a bias for calcium mobilization over cAMP production will function as non-stimulatory anxiolytics that augment memory formation.

Intra-amygdala microinfusion of neuropeptide S attenuates neuropathic pain and suppresses the response of spinal microglia and astrocytes after spinal nerve ligation in rats

The amygdala circuitry and neuropeptide S (NPS) have been shown to play an important role in the pain modulation. However, the alleviative effect of NPS in amygdala on neuropathic pain (NP) is not fully understood. Here, we demonstrate a possibility that the intra-amygdala microinfusion of NPS attenuates NP symptoms and suppresses the response of spinal microglia and astrocytes after spinal nerve injury. Spinal nerve ligation (SNL) in rats resulted in a striking decline in level of NPS and density of NPS-immunopositive cells in amygdala. SNL rats randomly received chronic bilateral microinjections of NPS (1, 10 and 100pmol/side) or saline into the amygdala via cannulas on days 3, 6, 9, 12, 15 and 18 post-surgery. Chronic treatment with NPS increased thermal withdrawal latency (TWL) and mechanical withdrawal threshold (MWT) on day 11-21 post-SNL. The simultaneous treatment with SHA68 as non-peptide NPS receptor antagonist decreased the TWL and MWT, and reversed the inhibitory effects of NPS in SNL rats. NPS also significantly attenuated immunoreactivities of ionized calcium-binding adapter molecule 1 and glial fibrillary acidic protein for microglia and astrocytes. Furthermore, the elevated levels of inflammatory mediators and expressions of nuclear factor κB p65 and CX3C chemokine receptor 1 due to SNL were significantly attenuated by NPS in amygdala. These effects of NPS were also counteracted by SHA 68. SHA 68 per se deteriorated the symptom of NP and the response of spinal microglia and astrocytes in SNL rats. Our study identified a protective role for NPS in amygdala against the development of NP, possibly attributing to its anti-inflammatory activity and inhibition of spinal microglia and astrocytes.

Neuropeptide S reduces fear and avoidance of con-specifics induced by social fear conditioning and social defeat, respectively

Neuropeptide S (NPS) has anxiolytic effects and facilitates extinction of cued fear in rodents. Here, we investigated whether NPS reverses social fear and social avoidance induced by social fear conditioning (SFC) and acute social defeat (SD), respectively, in male CD1 mice. Our results revealed that intracerebroventricular NPS (icv; 10 and 50 nmol/2 μl) reversed fear of unknown con-specifics induced by SFC and dose-dependently reduced avoidance of known aggressive con-specifics induced by SD. While 50 nmol of NPS completely reversed social avoidance and reinstated social preference, 10 nmol of NPS reduced social avoidance, but did not completely reinstate social preference in socially-defeated mice. Further, a lower dose (1 nmol/2 μl) of NPS facilitated the within-session extinction of cued fear, while a higher dose (10 nmol/2 μl) reduced the expression of cued fear. We could also confirm the anxiolytic effects of NPS (1, 10 and 50 nmol/2 μl) on the elevated plus-maze (EPM), which were not accompanied by alterations in locomotor activity either on the EPM or in the home cage. Finally, we could show that icv infusion of the NPS receptor 1 antagonist D-Cys((t)Bu)(5)-NPS (10 nmol/2 μl) did not alter SFC-induced social fear, general anxiety and locomotor activity. Taken together, our study extends the potent anxiolytic profile of NPS to a social context by demonstrating the reduction of social fear and social avoidance, thus providing the framework for studies investigating the involvement of the NPS system in the regulation of different types of social behaviour.

Activation of Hypocretin-1/Orexin-A Neurons Projecting to the Bed Nucleus of the Stria Terminalis and Paraventricular Nucleus Is Critical for Reinstatement of Alcohol Seeking by Neuropeptide S

BACKGROUND

Environmental conditioning is a major trigger for relapse in abstinent addicts. We showed that activation of the neuropeptide S (NPS) system exacerbates reinstatement vulnerability to cocaine and alcohol via stimulation of the hypocretin-1/orexin-A (Hcrt-1/Ox-A) system.

METHODS

Combining pharmacologic manipulations with immunohistochemistry techniques, we sought to determine how NPS and Hcrt-1/Ox-A systems interact to modulate reinstatement of alcohol seeking in rats.

RESULTS

Intrahypothalamic injection of NPS facilitated discriminative cue-induced reinstatement of alcohol seeking. This effect was blocked by the selective Hcrt-1/Ox-A antagonist SB334867 microinjected into the hypothalamic paraventricular nucleus (PVN) or into the bed nucleus of the stria terminalis (BNST) but not into the ventral tegmental area or the locus coeruleus. Combining double labeling and confocal microscopy analyses, we found that NPS-containing axons are in close apposition to hypothalamic Hcrt-1/Ox-A positive neurons, a significant proportion of which express NPS receptors, suggesting a direct interaction between the two systems. Retrograde tracing experiments showed that intra-PVN or intra-BNST red fluorobead unilateral injection labeled bilaterally Hcrt-1/Ox-A somata, suggesting that NPS could recruit two distinct neuronal pathways. Confirming this assumption, intra-BNST or PVN Hcrt-1/Ox-A injection enhanced alcohol seeking similarly to hypothalamic NPS injection but to a lesser degree.

CONCLUSIONS

Results suggest that the Hcrt-1/Ox-A neurocircuitry mediating the facilitation of cue-induced reinstatement by NPS involves structures critically involved in stress regulation such as the PVN and the BNST. These findings open to the tempting hypothesis of a role of the NPS system in modulating the interactions between stress and environmental conditioning factors in drug relapse.

Emerging targets for addiction neuropharmacology: From mechanisms to therapeutics

Drug abuse represents a considerable burden of disease and has enormous economic impacts on societies. Over the years, few medications have been developed for clinical use. Their utilization is endowed with several limitations, including partial efficacy or significant side effects. On the other hand, the successful advancement of these compounds provides an important proof of concept for the feasibility of drug development programs in addiction. In recent years, a wealth of information has been generated on the psychological mechanisms, genetic or epigenetic predisposing factors, and neurobiological adaptations induced by drug consumption that interact with each other to contribute to disease progression. It is now clear that addiction develops through phases, from initial recreational use to excessive consumption and compulsive drug seeking, with a shift from positive to negative reinforcement driving motivated behaviors. A greater understanding of these mechanisms has opened new vistas in drug development programs. Researchers' attention has been shifted from investigation of classical targets associated with reward to biological substrates responsible for negative reinforcement, impulse loss of control, and maladaptive mechanisms resulting from protracted drug use. From this research, several new biological targets for the development of innovative therapies have started to emerge. This chapter offers an overview of targets currently under scrutiny for the development of new medications for addiction. This work is not exhaustive but rather it provides a few examples of how this research has advanced in recent years by virtue of studies carried out in our laboratory.

Neuroleptics Affect Neuropeptide S and NPSR mRNA Levels in the Rat Brain

Neuropeptide S (NPS) has a multidirectional regulatory activity, especially when considered as a potent endogenous anxiolytic factor. Accumulating data suggests that neuroleptics affect peptidergic signaling in various brain structures. However, there is no information regarding the influence of treatment with antipsychotics on brain NPS expression. In the current study, we assessed the NPS and NPS receptor (NPSR) mRNA levels in the brains of rats shortly and chronically treated with chlorpromazine and olanzapine using quantitative real-time PCR. Both single-dose and long-term (4 months) olanzapine treatment led to the upregulation of NPS expression in the rat hypothalamus. It supports the hypothesis that NPS is involved in the dopamine-dependent anxiolytic actions of selected neuroleptics and possibly also in the pathophysiology of mental disorders. On the other hand, NPSR expression decreased after single-dose and chronic chlorpromazine administration in the hypothalamus, as well as after chronic olanzapine and chlorpromazine administration in the striatum and hippocampus. These results cast a new light on the pharmacology of antipsychotics and contribute to a better understanding of the mechanisms responsible for their action. Furthermore, our findings underline the complex nature of potential interactions between dopamine receptors and brain peptidergic pathways, which has potential clinical applications.

Neuropeptide S reduces mouse aggressiveness in the resident/intruder test through selective activation of the neuropeptide S receptor

Neuropeptide S (NPS) regulates various biological functions by selectively activating the NPS receptor (NPSR). In particular NPS evokes robust anxiolytic-like effects in rodents together with a stimulant and arousal promoting action. The aim of the study was to investigate the effects of NPS on the aggressiveness of mice subjected to the resident/intruder test. Moreover the putative role played by the endogenous NPS/NPSR system in regulating mice aggressiveness was investigating using mice lacking the NPSR receptor (NPSR(-/-)) and the NPSR selective antagonists [(t)Bu-D-Gly(5)]NPS and SHA 68. NPS (0.01-1 nmol, icv) reduced, in a dose dependent manner, both the time that resident mice spent attacking the intruder mice and their number of attacks, producing pharmacological effects similar to those elicited by the standard anti-aggressive drug valproate (300 mg/kg, ip). This NPS effect was evident in NPSR wild type (NPSR(+/+)) mice but completely disappeared in NPSR(-/-) mice. Moreover, NPSR(-/-) mice displayed a significantly higher time spent attacking than NPSR(+/+) mice. [(t)Bu-D-Gly(5)]NPS (10 nmol, icv) did not change the behavior of mice in the resident/intruder test but completely counteracted NPS effects. SHA 68 (50 mg/kg, ip) was inactive per se and against NPS. In conclusion, this study demonstrated that NPS produces anti-aggressive effects in mice through the selective activation of NPSR and that the endogenous NPS/NPSR system can exert a role in the control of aggressiveness levels under the present experimental conditions.

Modulation of prefrontal functioning in attention systems by NPSR1 gene variation. Neuroimage. 2015;114:199-206. [PMID: 25842293 DOI: 10.1016/j.neuroimage.2015.03.064]

Evidence has accumulated for a dysfunction of arousal and executive attention in anxiety. The neuropeptide S (NPS) system has been shown to play a pivotal role in the mediation of arousal and to be associated with anxiety/panic disorder. The present study aims at investigating the impact of functional neuropeptide S receptor (NPSR1) gene variation on neural attention patterns applying an imaging genetics approach. In an event-related functional magnetic resonance imaging (fMRI) setting, 47 healthy subjects (f=23) evenly pre-stratified for NPSR1 rs324981 A/T genotype were investigated for brain activation patterns while performing the Attention Network Task (ANT), simultaneously probing alerting and executive control functions. Anxiety sensitivity was ascertained by the Anxiety Sensitivity Index (ASI). In the alerting condition, NPSR1 TT homozygotes showed higher activations in the right prefrontal cortex and the locus coeruleus region as compared to A allele carriers. In the executive control condition, TT homozygotes displayed increased activations in fronto-parietal regions. Genotype-driven activation differences in the prefrontal cortex correlated with anxiety sensitivity, in both the alerting and the executive control system. The present results for the first time suggest NPSR1 gene variation to be associated with alterations of prefrontal functioning in the attentional functions alerting and executive control partly modulated by anxiety sensitivity. These findings may aid in unraveling the neurobiological underpinnings of distorted arousal and attention in anxiety and thereby possibly in the biomarker-guided development of preventive/therapeutic strategies targeting attention processes in anxiety disorders.

Evolutionary history of the neuropeptide S receptor/neuropeptide S system

The neuropeptide S receptor (NPSR) belongs to the G protein-coupled receptor (GPCR) superfamily and is activated by the neuropeptide S (NPS). Although recently discovered, the vertebrate NPSR-NPS system has been established as an important signaling system in the central nervous system and is involved in physiological processes such as locomotor activity, wakefulness, asthma pathogenesis, anxiety and food intake. The availability of a large number of genome sequences from multiple bilaterian lineages has provided an opportunity to establish the evolutionary history of the system. This review describes the origin and the molecular evolution of the NPSR-NPS system using data derived primarily from comparative genomic analyses. These analyses indicate that the NPSR-NPS system and the vasopressin-like receptor-vasopressin/oxytocin peptide (VPR-VP/OT) system originated from a single system in an ancestral bilaterian. Multiple duplications of this ancestral system gave rise to the bilaterian VPR-VP/OT system and to the protostomian cardioacceleratory peptide receptor-cardioacceleratory peptide (CCAPR-CCAP) system and to the NPSR-NPS system in the deuterostomes. Gene structure features of the receptors were consistent with the orthology annotations derived from phylogenetic analyses. The orthology of the peptide precursors closely paralleled that of the receptors suggesting an ancient coevolution of the receptor-peptide pair. An important challenge for the coevolution hypothesis will be to establish the molecular and structural basis of the divergence between orthologous receptor-ligand pairs in this system.

Effects of the neuropeptide S receptor antagonist RTI-118 on abuse-related facilitation of intracranial self-stimulation produced by cocaine and methylenedioxypyrovalerone (MDPV) in rats

Neuropeptide S (NPS) is a neurotransmitter that activates the NPS receptor to modulate biological functions including anxiety-like behaviors, feeding, and drug reinforcement. RTI-118 is a novel NPS receptor antagonist that decreased cocaine self-administration in rats at doses that had little or no effect on food-maintained responding. To build on these previous findings, this study examined effects of RTI-118 on cocaine-induced facilitation of intracranial self-stimulation (ICSS) in rats. To provide a context for data interpretation, effects of RTI-118 were compared to effects of the kappa opioid receptor agonist U69,593, because the kappa opioid receptor is another peptide neurotransmitter receptor reported to modulate abuse-related cocaine effects. RTI-118 effects were also examined on ICSS facilitation produced by methylenedioxypyrovalerone (MDPV), a novel designer drug of abuse with some cocaine-like effects. Male Sprague-Dawley rats (n=12) with electrodes targeting the medial forebrain bundle responded under a fixed-ratio 1 schedule for range of brain stimulation frequencies. Under control conditions, brain stimulation maintained a frequency-dependent increase in ICSS rates. Cocaine (1.0-10mg/kg) and MDPV (3.2mg/kg) facilitated ICSS. RTI-118 (3.2-32mg/kg) alone produced little effect on ICSS but dose dependently blocked cocaine-induced ICSS facilitation. U69,593 (0.25-0.5mg/kg) also attenuated cocaine effects, but blockade of cocaine effects was incomplete even at a U69,593 dose that alone depressed ICSS. RTI-118 (32mg/kg) failed to block MDPV-induced ICSS facilitation. These results support further consideration of NPS receptor antagonists as candidate treatments for cocaine abuse and provide evidence for differential effects of a candidate treatment on abuse-related effects of cocaine and MDPV.

Central adenosine A1 and A2A receptors mediate the antinociceptive effects of neuropeptide S in the mouse formalin test

AIMS

The present study aimed to investigate the intraplantar (ipl) and central (icv) effects of neuropeptide S (NPS) in the formalin test and to evaluate the role of adenosine receptors, mainly A1 and A2A, in mediating such effects.

MAIN METHODS

The ipl injection of formalin was used to assess the nociceptive activity. Moreover, by pretreating mice with non-selective and selective antagonists of adenosine receptors, the effects of icv NPS on formalin-induced ongoing nociception were assessed.

KEY FINDINGS

Morphine-induced antinociceptive effects were observed during phases 1 and 2 of the test, while indomethacin was active only at the later nociceptive phase. The ipl injection of NPS (alone or combined with formalin) did not modify the nociceptive response. However, icv NPS significantly reduced formalin-induced nociception during both phases. Caffeine (3 mg/kg, ip), a non-selective adenosine receptor antagonist, prevented NPS-induced antinociceptive effects. Similar to caffeine, icv ZM241385 (0.01 nmol), an A2A receptor antagonist, prevented the antinociceptive effects of NPS. Moreover, icv DPCPX (0.001 nmol), an A1 receptor antagonist, blocked the effects of NPS only during phase 1.

SIGNIFICANCE

The above findings suggest that: (i) NPS evokes central antinociceptive effects by activating both A1 and A2A receptors during phase 1, but (ii) only the adenosine A2A receptor during phase 2 of the formalin test.

Endogenous neuropeptide S tone influences sleep-wake rhythm in rats

Neuropeptide S (NPS) is an endogenous peptide that exerts wakefulness promoting, analgesic, and anxiolytic effects when administered exogenously. However, it remains to be determined if endogenous NPS tone is involved in the control of the diurnal sleep-wake cycle, or spontanous behavior. In this study, we examined the effects of the NPS receptor antagonist [D-Cys((t)Bu)(5)]NPS (2 and 20 nmol, icv) on physiological sleep and spontaneous locomotor behavior. The higher dose of [D-Cys((t)Bu)(5)]NPS decreased the amount of time spent in wakefulness [control 782.5 ± 25.5 min, treatment 751.7 ± 28.1 min; p<0.05] and increased the time spent in NREMS [control 572.6 ± 17.2 min, treatment 600.2 ± 26.1 min; p<0.05]. There was no statistically significant difference in time spent in REMS. There were no behavioral changes including abnormal gross motor behavior in response to [D-Cys((t)Bu)(5)]NPS administration. Collectively these data suggest an involvement of the endogenous NPS/NPS receptor system in physiological sleep architecture.

Persistent nociception induces anxiety-like behavior in rodents: role of endogenous neuropeptide S

Anxiety disorder is a comorbid condition of chronic pain. Analgesics and anxiolytics, subject to addiction and abuse, are currently used to manage pain and anxiety symptoms. However, the cellular mechanism underlying chronic pain and anxiety interaction remains to be elucidated. We report that persistent nociception following peripheral nerve injury induced anxiety-like behavior in rodents. Brain expression and release of neuropeptide S (NPS), a proposed endogenous anxiolytic peptide, was diminished in rodents with coexisting nociceptive and anxiety-like behaviors. Intracerebroventricular administration of exogenous NPS concurrently improved both nociceptive and anxiety-like behaviors. At the cellular level, NPS enhanced intra-amygdaloidal inhibitory transmission by increasing presynaptic gamma-aminobutyric acid (GABA) release from interneurons. These findings indicate that the interaction between nociceptive and anxiety-like behaviors in rodents may be regulated by the altered NPS-mediated intra-amygdaloidal GABAergic inhibition. The data suggest that enhancing the brain NPS function may be a new strategy to manage comorbid pain and anxiety.

Neuropeptide S counteracts 6-OHDA-induced motor deficits in mice

Neuropeptide S (NPS) is a 20-aminoacid peptide that selectively activates a G-protein coupled receptor named NPSR. Preclinical studies have shown that NPSR activation promotes anxiolysis, hyperlocomotion, arousal and weakfullness. Previous findings suggest that dopamine neurotransmission plays a role in the actions of NPS. Based on the close relationship between dopamine and Parkinson disease (PD) and on the evidence that NPSR are expressed on brain dopaminergic nuclei, the present study investigated the effects of NPS in motor deficits induced by intracerebroventricular (icv) administration of the dopaminergic neurotoxin 6-OHDA in the mouse rotarod test. 6-OHDA injection evoked motor deficits and significantly reduced tyrosine hidroxylase (TH)-positive cells in the substantia nigra (SN) and ventral tegmental area. However, a positive correlation was found only between the motor performance of 6-OHDA-injected mice and the number of TH-positive cells in SN. The systemic administration of l-DOPA+benserazide (25+6.25 mg/kg) counteracted 6-OHDA-induced motor deficits in mice. Similar to L-DOPA, the icv injection of NPS (0.1 and 1 nmol) reversed motor deficits evoked by 6-OHDA. In conclusion, NPS attenuated 6-OHDA-induced motor impairments in mice assessed in the rota-rod test. We discussed the beneficial actions of NPS based on a putative facilitation of dopaminergic neurotransmission in the brain. Finally, these findings candidate NPSR agonists as a potential innovative treatment for PD.

A functional NPSR1 gene variant and environment shape personality and impulsive action: a longitudinal study

Neuropeptide S and its receptor NPSR1 are involved in the regulation of arousal, attention and anxiety. We examined whether the NPSR1 gene functional polymorphism Asn¹⁰⁷Ile (rs324981, A>T) influences personality, impulsivity, and attention-deficit/hyperactivity disorder (ADHD)-related symptoms in a population-representative sample, and whether any eventual associations depend on age, sex, family relations and stressful life events (SLE). We used self-reports or teachers' ratings for both the younger (n=593) and older (n=583) cohort of the longitudinal Estonian Children Personality, Behaviour and Health Study. Males with the TT genotype displayed more ADHD-related symptoms. Adaptive impulsivity and Extraversion increased the most from age 18 to 25. While highest increases were observed in AA men, TT women exhibited the largest decreases. For participants with the AA genotype, Warmth in family was inversely associated with Neuroticism, and positively associated with Extraversion and Adaptive impulsivity. High exposure to SLE increased impulsivity and ADHD scores in TT genotype subjects. We conclude that the NPSR1 A/T polymorphism is associated with impulsivity, ADHD symptoms and personality, mirroring the activity- and anxiety-mediating role of NPSR1. Heterozygous individuals were the least sensitive to environmental factors, whereas subjects with the AA genotype and TT genotype reacted to different types of environmental adversities.

In vitro and in vivo pharmacological characterization of the novel neuropeptide S receptor ligands QA1 and PI1

The pharmacological activity of the novel neuropeptide S (NPS) receptor (NPSR) ligands QA1 and PI1 was investigated. In vitro QA1 and PI1 were tested in calcium mobilization studies performed in HEK293 cells expressing the recombinant mouse (HEK293mNPSR) and human (HEK293hNPSRIle107 and HEK293hNPSRAsn107) NPSR receptors. In vivo the compounds were studied in mouse righting reflex (RR) and locomotor activity (LA) tests. NPS caused a concentration dependent mobilization of intracellular calcium in the three cell lines with high potency (pEC50 8.73-9.14). In inhibition response curve and Schild protocol experiments the effects of NPS were antagonized by QA1 and PI1. QA1 displayed high potency (pKB 9.60-9.82) behaving as a insurmountable antagonist. However in coinjection experiments QA1 produced a rightward swift of the concentration response curve to NPS without modifying its maximal effects; this suggests that QA1 is actually a slow dissociating competitive antagonist. PI1 displayed a competitive type of antagonism and lower values of potencies (pA2 7.74-8.45). In vivo in mice NPS (0.1 nmol, i.c.v.) elicited arousal promoting action in the RR assay and stimulant effects in the LA test. QA1 (30 mgkg(-1)) was able to partially counteract the arousal promoting NPS effects, while PI1 was inactive in the RR test. In the LA test QA1 and PI1 only poorly blocked the NPS stimulant action. The present data demonstrated that QA1 and PI1 act as potent NPSR antagonists in vitro, however their usefulness for in vivo investigations in mice seems limited probably by pharmacokinetic reasons.