Neuropeptide S-mediated control of fear expression and extinction: role of intercalated GABAergic neurons in the amygdala

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.

Diverse roles of pontine NPS-expressing neurons in sleep regulation

Neuropeptide S (NPS) was postulated to be a wake-promoting neuropeptide with unknown mechanism, and a mutation in its receptor (NPSR1) causes the short sleep duration trait in humans. We investigated the role of different NPS+ nuclei in sleep/wake regulation. Loss-of-function and chemogenetic studies revealed that NPS+ neurons in the parabrachial nucleus (PB) are wake-promoting, whereas peri-locus coeruleus (peri-LC) NPS+ neurons are not important for sleep/wake modulation. Further, we found that a NPS+ nucleus in the central gray of the pons (CGPn) strongly promotes sleep. Fiber photometry recordings showed that NPS+ neurons are wake-active in the CGPn and wake/REM-sleep active in the PB and peri-LC. Blocking NPS-NPSR1 signaling or knockdown of Nps supported the function of the NPS-NPSR1 pathway in sleep/wake regulation. Together, these results reveal that NPS and NPS+ neurons play dichotomous roles in sleep/wake regulation at both the molecular and circuit levels.

A cluster of neuropeptide S neurons regulates breathing and arousal

Neuropeptide S (NPS) is a highly conserved peptide found in all tetrapods that functions in the brain to promote heightened arousal; however, the subpopulations mediating these phenomena remain unknown. We generated mice expressing Cre recombinase from the Nps gene locus (NpsCre) and examined populations of NPS+ neurons in the lateral parabrachial area (LPBA), the peri-locus coeruleus (peri-LC) region of the pons, and the dorsomedial thalamus (DMT). We performed brain-wide mapping of input and output regions of NPS+ clusters and characterized expression patterns of the NPS receptor 1 (NPSR1). While the activity of all three NPS+ subpopulations tracked with vigilance state, only NPS+ neurons of the LPBA exhibited both increased activity prior to wakefulness and decreased activity during REM sleep, similar to the behavioral phenotype observed upon NPSR1 activation. Accordingly, we found that activation of the LPBA but not the peri-LC NPS+ neurons increased wake and reduced REM sleep. Furthermore, given the extended role of the LPBA in respiration and the link between behavioral arousal and breathing rate, we demonstrated that the LPBA but not the peri-LC NPS+ neuronal activation increased respiratory rate. Together, our data suggest that NPS+ neurons of the LPBA represent an unexplored subpopulation regulating breathing, and they are sufficient to recapitulate the sleep/wake phenotypes observed with broad NPS system activation.

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.

Selective breeding of rats for high (HAB) and low (LAB) anxiety-related behaviour: A unique model for comorbid depression and social dysfunctions

Animal models of selective breeding for extremes in emotionality are a strong experimental approach to model psychopathologies. They became indispensable in order to increase our understanding of neurobiological, genetic, epigenetic, hormonal, and environmental mechanisms contributing to anxiety disorders and their association with depressive symptoms or social deficits. In the present review, we extensively discuss Wistar rats selectively bred for high (HAB) and low (LAB) anxiety-related behaviour on the elevated plus-maze. After 30 years of breeding, we can confirm the prominent differences between HAB and LAB rats in trait anxiety, which are accompanied by consistent differences in depressive-like, social and cognitive behaviours. We can further confirm a single nucleotide polymorphism in the vasopressin promotor of HAB rats causative for neuropeptide overexpression, and show that low (or high) anxiety and fear levels are unlikely due to visual dysfunctions. Thus, HAB and LAB rats continue to exist as a reliable tool to study the multiple facets underlying the pathology of high trait anxiety and its comorbidity with depression-like behaviour and social dysfunctions.

Update on neurobiological mechanisms of fear: illuminating the direction of mechanism exploration and treatment development of trauma and fear-related disorders

Fear refers to an adaptive response in the face of danger, and the formed fear memory acts as a warning when the individual faces a dangerous situation again, which is of great significance to the survival of humans and animals. Excessive fear response caused by abnormal fear memory can lead to neuropsychiatric disorders. Fear memory has been studied for a long time, which is of a certain guiding effect on the treatment of fear-related disorders. With continuous technological innovations, the study of fear has gradually shifted from the level of brain regions to deeper neural (micro) circuits between brain regions and even within single brain regions, as well as molecular mechanisms. This article briefly outlines the basic knowledge of fear memory and reviews the neurobiological mechanisms of fear extinction and relapse, which aims to provide new insights for future basic research on fear emotions and new ideas for treating trauma and fear-related disorders.

Insights on benzodiazepines' potential in Alzheimer's disease

Alzheimer's disease (AD) is the most frequent type of dementia characterized by the deposition of amyloid beta (Aβ) plaque and tau-neurofibrillary tangles (TNTs) in the brain. AD is associated with the disturbances of various neurotransmitters including gamma-aminobutyric acid (GABA). Of note, GABA is reduced in AD, and restoration of GABA effect by benzodiazepines (BDZs) may improve AD outcomes. However, BDZs may adversely affect cognitive functions chiefly in elderly AD patients with sleep disorders. Besides, there is a controversy regarding the use of BDZs in AD. Consequently, the objective of the present review was to disclose the possible role of BDZs on the pathogenesis of AD that might be beneficial, neutral, or detrimental effects on AD. Prolonged use of intermediate-acting BDZ lorazepam exerts amnesic effects due to attenuation of synaptic plasticity and impairment of recognition memory. However, BDZs may have a protective effect against the development of AD by reducing tau phosphorylation, neuroinflammation, and progression of AD neuropathology. On the other side, other findings highlighted that extended use of BDZs was not associated with the development of AD. In conclusion, there are controversial points concerning the use of BDZs and the risk for the progression of AD. Thus, preclinical, and clinical studies are essential in this regard.

Amygdala Intercalated Cells: Gate Keepers and Conveyors of Internal State to the Circuits of Emotion

Generating adaptive behavioral responses to emotionally salient stimuli requires evaluation of complex associations between multiple sensations, the surrounding context, and current internal state. Neural circuits within the amygdala parse this emotional information, undergo synaptic plasticity to reflect learned associations, and evoke appropriate responses through their projections to the brain regions orchestrating these behaviors. Information flow within the amygdala is regulated by the intercalated cells (ITCs), which are densely packed clusters of GABAergic neurons that encircle the basolateral amygdala (BLA) and provide contextually relevant feedforward inhibition of amygdala nuclei, including the central and BLA. Emerging studies have begun to delineate the unique contribution of each ITC cluster and establish ITCs as key loci of plasticity in emotional learning. In this review, we summarize the known connectivity and function of individual ITC clusters and explore how different neuromodulators conveying internal state act via ITC gates to shape emotionally motivated behavior. We propose that the behavioral state-dependent function of ITCs, their unique genetic profile, and rich expression of neuromodulator receptors make them potential therapeutic targets for disorders, such as anxiety, schizophrenia spectrum, and addiction.

The association between genetic variability in the NPS/NPSR1 system and chronic stress responses: A gene-environment-(quasi-) experiment

The neuropeptide S (NPS) and its receptor (NPSR1) have been implicated in stress regulation and stress-related disorders. The present study aimed at investigating the association between overall genetic variability in the NPS/NPSR1 system and psychological and cortisol stress regulation in everyday life. Our study was conceptualized as a gene-environment-(quasi-) experiment, a design that facilitates the detection of true GxE interactions. As environmental variable, we used the preparation for the first state examination for law students. In the prospective and longitudinal LawSTRESS project, students were examined at six sampling points over a 13-months period. While students who prepared for the exam and experienced long-lasting and significant stress, formed the stress group, law students experiencing usual study-related workload were assigned to the control group. As phenotypes we assessed changes over time in the cortisol awakening response (CAR; n = 176), perceived stress levels (n = 401), and anxiety symptoms (n = 397). The CAR was assessed at each sampling point immediately upon awakening and 30 as well as 45 min later. Perceived stress levels in daily life were measured by repeated ambulatory assessments and anxiety symptoms were repeatedly assessed with the anxiety subscale of the Hospital Anxiety and Depression Scale. With gene-set analyses we examined the joint association of 936 NPS/NPSR1 single nucleotide polymorphisms with the phenotypes to overcome well known limitations of candidate gene studies. As previously reported, we found a blunted CAR during the exam as well as significant increases in perceived stress levels and anxiety symptoms until the exam in the stress group, compared to the control group. The gene-set analysis did not confirm associations between genetic variability in the NPS/NPSR1 system and changes in perceived stress levels and anxiety symptoms. Regarding the CAR, we found a significant GxE interaction for the area under the curve with respect to the ground (p = .050) and a trend towards a significant effect for the area under the curve with respect to the increase (p = .054). When the analysis was restricted to the SG, associations for both CAR parameters were significant (ps < .050). This finding suggests that the association between genetic variability in the NPS/NPSR1 system and the CAR becomes visible under the environmental condition 'chronic stress exposure'. We conclude that the present study complements findings from animal models and that it provides novel evidence for a modulatory influence of the NPS/NPSR1 system on cortisol regulation in humans.

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.

A Role for Neuropeptide S in Alcohol and Cocaine Seeking

The neuropeptide S (NPS) is the endogenous ligand of the NPS receptor (NPSR). The NPSR is widely expressed in brain regions that process emotional and affective behavior. NPS possesses a unique physio-pharmacological profile, being anxiolytic and promoting arousal at the same time. Intracerebroventricular NPS decreased alcohol consumption in alcohol-preferring rats with no effect in non-preferring control animals. This outcome is most probably linked to the anxiolytic properties of NPS, since alcohol preference is often associated with high levels of basal anxiety and intense stress-reactivity. In addition, NPSR mRNA was overexpressed during ethanol withdrawal and the anxiolytic-like effects of NPS were increased in rodents with a history of alcohol dependence. In line with these preclinical findings, a polymorphism of the NPSR gene was associated with anxiety traits contributing to alcohol use disorders in humans. NPS also potentiated the reinstatement of cocaine and ethanol seeking induced by drug-paired environmental stimuli and the blockade of NPSR reduced reinstatement of cocaine-seeking. Altogether, the work conducted so far indicates the NPS/NPSR system as a potential target to develop new treatments for alcohol and cocaine abuse. An NPSR agonist would be indicated to help individuals to quit alcohol consumption and to alleviate withdrawal syndrome, while NPSR antagonists would be indicated to prevent relapse to alcohol- and cocaine-seeking behavior.

Neuropeptide S Encodes Stimulus Salience in the Paraventricular Thalamus

Evaluation of stimulus salience is critical for any higher organism, as it allows for prioritizing of vital information, preparation of responses, and formation of valuable memory. The paraventricular nucleus of the thalamus (PVT) has recently been identified as an integrator of stimulus salience but the neurochemical basis and afferent input regarding salience signaling have remained elusive. Here we report that neuropeptide S (NPS) signaling in the PVT is necessary for stimulus salience encoding, including aversive, neutral and reinforcing sensory input. Taking advantage of a striking deficit of both NPS receptor (NPSR1) and NPS precursor knockout mice in fear extinction or novel object memory formation, we demonstrate that intra-PVT injections of NPS can rescue the phenotype in NPS precursor knockout mice by increasing the salience of otherwise low-intensity stimuli, while intra-PVT injections of NPSR1 antagonist in wild type mice partially replicates the knockout phenotype. The PVT appears to provide stimulus salience encoding in a dose- and NPS-dependent manner. PVT NPSR1 neurons recruit the nucleus accumbens shell and structures in the prefrontal cortex and amygdala, which were previously linked to the brain salience network. Overall, these results demonstrate that stimulus salience encoding is critically associated with NPS activity in the PVT.

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.

Can Neuropeptide S Be an Indicator for Assessing Anxiety in Psychiatric Disorders?

Neuropeptide S (NPS) is a neuropeptide primarily produced within three brainstem regions including locus coeruleus, trigeminal nerve nucleus, and lateral parabrachial nucleus. NPS is involved in the central regulation of stress, fear, and cognitive integration. NPS is a mediator of behavior, seeking food, and the proliferation of new adipocytes in the setting of obesity. So far, current research of NPS is only limited to animal models; data regarding its functions in humans is still scarce. Animal studies showed that anxiety and appetite might be suppressed by the action of NPS. The discovery of this neuromodulator peptide is effective considering its strong anxiolytic action, which has the potential to be an interesting therapeutic option in treating neuropsychiatric disorders. In this article, we aimed to analyze the pharmaceutical properties of NPS as well as its influence on several neurophysiological aspects-modulation of behavior, association with obesity, as well as its potential application in rehabilitation and treatment of psychiatric disorders.

The influence of early-life and adulthood stressors on brain neuropeptide-S system

Central administered neuropeptide-S (NPS) was shown to reduce stress response in rodents. This study aimed to investigate the alterations in NPS system upon chronic exposure to early-life and adulthood stressors. Newborn pups underwent maternal separation (MS) from postnatal day 1 to 14 comprised of daily 3-h separations. In the adulthood, 90-min of restraint stress was loaded to males as an acute stress (AS) model. For chronic homotypic stress (CHS), same stressor was applied for 5 consecutive days. The changes in the expression and the release of NPS were monitored by immunohistochemistry and microdialysis, respectively. Throughout the CHS, heart rate variability (HRV) was analyzed on a daily basis. The immunoreactivity for NPS receptor (NPSR) was detected in basolateral amygdala (BLA) and hypothalamic paraventricular nucleus (PVN) by immunofluorescence staining. The NPS expression in the brainstem was increased upon AS which was more prominent following CHS, whereas these responses were found to be blunted in MS counterparts. Similar to histological data, the stress-induced release of NPS in BLA was attenuated in MS rats. CHS-induced elevations in sympatho-vagal balance were alleviated in control rats; which was not observed in MS rats. The expression of NPSR in BLA and PVN was down-regulated in MS rats. The brain NPS/NPSR system appears to be susceptible to the early-life stressors and the subsequent chronic stress exposure in adulthood which results in altered autonomic outflow.

Centrally Administered Neuropeptide-S Alleviates Gastrointestinal Dysmotility Induced by Neonatal Maternal Separation

BACKGROUND

Neuropeptide-S (NPS) regulates autonomic outflow, stress response, and gastrointestinal (GI) motor functions. This study aimed to investigate the effects of NPS on GI dysmotility induced by neonatal maternal separation (MS).

METHODS

MS was conducted by isolating newborn pups from dams from postnatal day 1 to day 14. In adulthood, rats were also exposed to chronic homotypic stress (CHS). Visceral sensitivity was assessed by colorectal distension-induced abdominal contractions. Gastric emptying (GE) was measured following CHS, whereas fecal output was monitored daily. NPS or NPS receptor (NPSR) antagonist was centrally applied simultaneously with electrocardiography and gastric motility recording. Immunoreactivities for NPS, NPSR, corticotropin-releasing factor (CRF), choline acetyltransferase (ChAT), tyrosine hydroxylase (TH), and c-Fos were assessed by immunohistochemistry.

KEY RESULTS

NPS alleviated the MS-induced visceral hypersensitivity. Under basal conditions, central exogenous or endogenous NPS had no effect on GE and gastric motility. NPS restored CHS-induced gastric and colonic dysmotility in MS rats while increasing sympatho-vagal balance without affecting vagal outflow. NPSR expression was detected in CRF-producing cells of hypothalamic paraventricular nucleus, and central amygdala, but not in Barrington's nucleus. Moreover, NPSR was present in ChAT-expressing neurons in dorsal motor nucleus of the vagus (DMV), and nucleus ambiguus (NAmb) in addition to the TH-positive neurons in C1/A1, and locus coeruleus (LC). Neurons adjacent to the adrenergic cells in LC were found to produce NPS. NPS administration caused c-Fos expression in C1/A1 cells, while no immunoreactivity was detected in DMV or NAmb.

CONCLUSIONS

NPS/NPSR system might be a novel target for the treatment of stress-related GI dysmotility.

Neuropeptide-S affects cognitive impairment and depression-like behavior on MPTP induced experimental mouse model of Parkinson’s disease

Background/aim

The present study proposes to investigate the effect of neuropeptide–S (NPS) on cognitive functions and depression-like behavior of MPTP-induced experimental model of Parkinson’s disease (PD).

Materials and methods

Three-month-old C57BL/6 mice were randomly divided into three groups as; Control, Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and MPTP + NPS 0.1 nmol (received intraperitoneal injection of MPTP and intracerebroventricular injection of NPS, 0.1 nmol for seven days). The radial arm maze and pole tests were carried out, and the levels of tyrosine hydroxylase (TH) were determined using western blotting. A mass spectrometer was used to measure the levels of dopamine, glutamic acid, and glutamine.

Results

The T-turn and time to descend enhanced in MPTP group, while these parameters were decreased by NPS treatment. In the MPTP group, the number of working memory errors (WME) and reference memory errors (RME) increased, whereas NPS administration decreased both parameters. Sucrose preference decreased in the MPTP group while increasing in the NPS group. MPTP injection significantly reduced dopamine, glutamic acid, and glutamine levels. NPS treatment restored the MPTP-induced reduction in glutamine and glutamic acid levels.

Conclusion

NPS may be involved in the future treatment of cognitive impairments and depression-like behaviors in PD.

Role of the Neuropeptide S System in Emotionality, Stress Responsiveness and Addiction-Like Behaviours in Rodents: Relevance to Stress-Related Disorders

The neuropeptide S (NPS) and its receptor (NPSR1) have been extensively studied over the last two decades for their roles in locomotion, arousal/wakefulness and anxiety-related and fear-related behaviours in rodents. However, the possible implications of the NPS/NPSR1 system, especially those of the single nucleotide polymorphism (SNP) rs324981, in stress-related disorders and substance abuse in humans remain unclear. This is possibly due to the fact that preclinical and clinical research studies have remained separated, and a comprehensive description of the role of the NPS/NPSR1 system in stress-relevant and reward-relevant endpoints in humans and rodents is lacking. In this review, we describe the role of the NPS/NPSR1 system in emotionality, stress responsiveness and addiction-like behaviour in rodents. We also summarize the alterations in the NPS/NPSR1 system in individuals with stress-related disorders, as well as the impact of the SNP rs324981 on emotion, stress responses and neural activation in healthy individuals. Moreover, we discuss the therapeutic potential and possible caveats of targeting the NPS/NPSR1 system for the treatment of stress-related disorders. The primary goal of this review is to highlight the importance of studying some rodent behavioural readouts modulated by the NPS/NPSR1 system and relevant to stress-related disorders.

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.

Deletion of ErbB4 Disrupts Synaptic Transmission and Long-Term Potentiation of Thalamic Input to Amygdalar Medial Paracapsular Intercalated Cells

Identification of candidate risk genes and alteration in the expression of proteins involved in regulating inhibitory neuron function in various psychiatric disorders, support the notion that GABAergic neuron dysfunction plays an important role in disease etiology. Genetic variations in neuregulin and its receptor kinase ErbB4, expressed exclusively by GABAergic neurons in the CNS, have been linked with schizophrenia. In the amygdala, ErbB4 is highly expressed in GABAergic intercalated cell clusters (ITCs), which play a critical role in amygdala-dependent behaviors. It is however unknown whether ErbB4 deletion from ITCs affects their synaptic properties and function in amygdala circuitry. Here, we examined the impact of ErbB4 deletion on inhibitory and excitatory circuits recruiting medial paracapsular ITCs (mpITCs) using electrophysiological techniques. Ablation of ErbB4 in mpITCs suppressed NMDA receptor-mediated synaptic transmission at thalamo-mpITC synapses and enhanced thalamic driven GABAergic transmission onto mpITCs. Furthermore, long-term potentiation (LTP) at thalamo-mpITC synapses was compromised in ErbB4 mutant mice, indicating that ErbB4 activity is critical for LTP at these synapses. Together, our findings suggest that ErbB4 deletion from mpITCs disrupts excitation-inhibition balance and learning mechanisms in amygdala circuits.

Dissociative Effects of Neuropeptide S Receptor Deficiency and Nasal Neuropeptide S Administration on T-Maze Discrimination and Reversal Learning

Cognitive flexibility refers to the ability to modify learned behavior in response to changes in the environment. In laboratory rodents, cognitive flexibility can be assessed in reversal learning, i.e., the change of contingencies, for example in T-maze discrimination learning. The present study investigated the role of the neuropeptide S (NPS) system in cognitive flexibility. In the first experiment, mice deficient of NPS receptors (NPSR) were tested in T-maze discrimination and reversal learning. In the second experiment, C57BL/6J mice were tested in the T-maze after nasal administration of NPS. Finally, the effect of nasal NPS on locomotor activity was evaluated. NPSR deficiency positively affected the acquisition of T-maze discrimination but had no effects on reversal learning. Nasal NPS administration facilitated reversal learning and supported an allocentric learning strategy without affecting acquisition of the task or locomotor activity. Taken together, the present data show that the NPS system is able to modulate both acquisition of T-maze discrimination and its reversal learning. However, NPSR deficiency only improved discrimination learning, while nasal NPS administration only improved reversal learning, i.e., cognitive flexibility. These effects, which at first glance appear to be contradictory, could be due to the different roles of the NPS system in the brain regions that are important for learning and cognitive flexibility.

Safety learning during development: Implications for development of psychopathology

Fear and safety learning are necessary adaptive behaviors that develop over the course of maturation. While there is a large body of literature regarding the neurobiology of fear and safety learning in adults, less is known regarding safety learning during development. Given developmental changes in the brain, there are corresponding changes in safety learning that are quantifiable; these may serve to predict risk and point to treatment targets for fear and anxiety-related disorders in children and adolescents. For healthy, typically developing youth, the main developmental variation observed is reduced discrimination between threat and safety cues in children compared to adolescents and adults, while lower expression of extinction learning is exhibited in adolescents compared to adults. Such distinctions may be related to faster maturation of the amygdala relative to the prefrontal cortex, as well as incompletely developed functional circuits between the two. Fear and anxiety-related disorders, childhood maltreatment, and behavioral problems are all associated with alterations in safety learning for youth, and this dysfunction may proceed into adulthood with corresponding abnormalities in brain structure and function-including amygdala hypertrophy and hyperreactivity. As impaired inhibition of fear to safety may reflect abnormalities in the developing brain and subsequent psychopathology, impaired safety learning may be considered as both a predictor of risk and a treatment target. Longitudinal neuroimaging studies over the course of development, and studies that query change with interventions are needed in order to improve outcomes for individuals and reduce long-term impact of developmental psychopathology.

Neuropeptide S Receptor Stimulation Excites Principal Neurons in Murine Basolateral Amygdala through a Calcium-Dependent Decrease in Membrane Potassium Conductance

Background: The neuropeptide S system, consisting of the 20 amino acid neuropeptide NPS and its G-protein-coupled receptor (GPCR) neuropeptide S receptor 1 (NPSR1), has been studied intensively in rodents. Although there is a lot of data retrieved from behavioral studies using pharmacology or genetic interventions, little is known about intracellular signaling cascades in neurons endogenously expressing the NPSR1. Methods: To elucidate possible G-protein-dependent signaling and effector systems, we performed whole-cell patch-clamp recordings on principal neurons of the anterior basolateral amygdala of mice. We used pharmacological interventions to characterize the NPSR1-mediated current induced by NPS application. Results: Application of NPS reliably evokes inward-directed currents in amygdalar neurons recorded in brain slice preparations of male and female mice. The NPSR1-mediated current had a reversal potential near the potassium reversal potential (E_K) and was accompanied by an increase in membrane input resistance. GDP-β-S and BAPTA, but neither adenylyl cyclase inhibition nor 8-Br-cAMP, abolished the current. Intracellular tetraethylammonium or 4-aminopyridine reduced the NPS-evoked current. Conclusion: NPSR1 activation in amygdalar neurons inhibits voltage-gated potassium (K⁺) channels, most likely members of the delayed rectifier family. Intracellularly, G_αq signaling and calcium ions seem to be mandatory for the observed current and increased neuronal excitability.

Self-assembling modified neuropeptide S enhances nose-to-brain penetration and exerts a prolonged anxiolytic-like effect

Anxiety disorders are the most common mental diseases and can greatly disrupt everyday life. Although there has been substantial research on anxiety disorders, novel therapeutics are needed. Neuropeptide S (NPS) is a potential therapeutic candidate owing to its strong anxiolytic activity; however, some disadvantages, such as its poor metabolic stability and inability to cross the blood-brain barrier (BBB), limit its use in the clinic. Herein, inspired by nose-to-brain drug delivery strategies, an endogenous 20-amino-acid-long mNPS peptide was modified by incorporating palmitic acid into its functional Lys¹² side chain (M-3), which was expected to facilitate nose-to-brain penetration and exert a prolonged anxiolytic-like effect compared to mNPS. We found that M-3 assembled into nanofibers that retained the bioactivity of NPS and exhibited obvious improvements in metabolic stability. Notably, as expected, self-assembled M-3 was able to penetrate into the brain and exert anxiolytic effects. The elevated plus-maze (EPM) results further revealed that M-3 could produce prolonged anxiolytic-like effects in mice. In vivo imaging studies revealed that self-assembled M-3 could be efficiently transported from the nasal cavity to the brain. Furthermore, when intranasally administered, this molecule exhibited a significantly prolonged anxiolytic-like effect, which further illustrated that this molecule has a potent nose-to-brain penetration in vivo. Overall, this self-assembled nanofiber showed potent nose-to-brain penetration ability and prolonged bioactivity.

Pharmacology, Physiology and Genetics of the Neuropeptide S System

The Neuropeptide S (NPS) system is a rather ‘young’ transmitter system that was discovered and functionally described less than 20 years ago. This review highlights the progress that has been made in elucidating its pharmacology, anatomical distribution, and functional involvement in a variety of physiological effects, including behavior and immune functions. Early on, genetic variations of the human NPS receptor (NPSR1) have attracted attention and we summarize current hypotheses of genetic linkage with disease and human behaviors. Finally, we review the therapeutic potential of future drugs modulating NPS signaling. This review serves as an introduction to the broad collection of original research papers and reviews from experts in the field that are presented in this Special Issue.

Biological Markers in Anxiety Disorders

Anxiety disorders are one of the most commonly reported disorders in psychiatry, causing a high medical and socio-economic burden. Recently, there has been a soaring interest in the biological basis of anxiety disorders, which is reflected in an increasing number of articles related to the topic. Due to the ambiguity of the diagnosis and a large number of underdiagnosed patients, researchers are looking for laboratory tests that could facilitate the diagnosis of anxiety disorders in clinical practice and would allow for the earliest possible implementation of appropriate treatment. Such potential biomarkers may also be useable in monitoring the efficacy of pharmacological therapy for anxiety disorders. Therefore this article reviews the literature of potential biomarkers such as components of saliva, peripheral blood, cerebrospinal fluid (CSF), and neuroimaging studies. There are promising publications in the literature that can be useful. The most valuable and promising markers of saliva are cortisol, lysozyme, and α-amylase (sAA). In the blood, in turn, we can distinguish serotonin, brain-derived serum neurotrophic factor (BDNF), cortisol, and microRNA. Structural changes in the amygdala and hippocampus are promising neuroimaging markers, while in CSF, potential markers include oxytocin and 5-Hydroxyindoleacetic acid (5-HIAA). Unfortunately, research in the field of biomarkers is hampered by insufficient knowledge about the etiopathogenesis of anxiety disorders, the significant heterogeneity of anxiety disorders, frequent comorbidities, and low specificity of biomarkers. The development of appropriate biomarker panels and their assessment using new approaches may have the prospective to overcome the above-mentioned obstacles.

Neandertal introgression and accumulation of hypomorphic mutations in the neuropeptide S (NPS) system promote attenuated functionality

The neuropeptide S (NPS) system plays an important role in fear and fear memory processing but has also been associated with allergic and inflammatory diseases. Genes for NPS and its receptor NPSR1 are found in all tetrapods. Compared to non-human primates, several non-synonymous single-nucleotide polymorphisms (SNPs) occur in both human genes that collectively result in functional attenuation, suggesting adaptive mechanisms in a human context. To investigate historic and geographic origins of these hypomorphic mutations and explore genetic signs of selection, we analyzed ancient genomes and worldwide genotype frequencies of four prototypic SNPs in the NPS system. Neandertal and Denisovan genomes contain exclusively ancestral alleles for NPSR1 while all derived alleles occur in ancient genomes of anatomically modern humans, indicating that they arose in modern Homo sapiens. Worldwide genotype frequencies for three hypomorphic NPSR1 SNPs show significant regional homogeneity but follow a gradient towards increasing derived allele frequencies that supports an out-of-Africa scenario. Increased density of high-frequency polymorphisms around the three NPSR1 loci suggests weak or possibly balancing selection. A hypomorphic mutation in the NPS precursor, however, was detected at high frequency in Eurasian Neandertal genomes and shows genetic signatures indicating that it was introgressed into the human gene pool, particularly in Southern Europe, by interbreeding with Neandertals. We discuss potential evolutionary scenarios including behavior and immune-based natural selection.

Dopamine in Fear Extinction

The ability to extinguish fear memories when threats are no longer present is critical for adaptive behavior. Fear extinction represents a new learning process that eventually leads to the formation of extinction memories. Understanding the neural basis of fear extinction has considerable clinical significance as deficits in extinction learning are the hallmark of human anxiety disorders. In recent years, the dopamine (DA) system has emerged as one of the key regulators of fear extinction. In this review article, we highlight recent advances that have demonstrated the crucial role DA plays in mediating different phases of fear extinction. Emerging concepts and outstanding questions for future research are also discussed.

The µ-opioid system in midline thalamic nuclei modulates defence strategies towards a conditioned fear stimulus in male mice

BACKGROUND

Nuclei located in the dorsal midline thalamus, such as the paraventricular nucleus of the thalamus (PVT), are crucial to modulate fear and aversive behaviour. In addition, the PVT shows a dense expression of µ-opioid receptors (MORs) and could mediate the anxiolytic effects of opioids.

METHODS

We analysed the contribution of MORs in the dorsal midline thalamus (i.e. the PVT) to the performance of mice in a classical fear conditioning paradigm. We locally injected a specific agonist (DAMGO), an antagonist (CTAP) of MOR or saline as a control into the dorsal midline thalamus of male mice, prior to fear extinction training. We assessed freezing as a typical measure of fear and extended our analysis by evaluation of aversive, non-aversive and neutral behavioural features using compositional data analysis.

RESULTS

Pharmacological blockade of MORs through CTAP in the dorsal midline thalamus induced a fear memory extinction deficit, as evidenced by maintained freezing during extinction sessions. Stimulation of MORs by DAMGO resulted in an overall increase in locomotor activity, associated with decreased freezing during recall of extinction. Compositional data analysis confirmed the freezing-related pharmacological effects and revealed specific differences in basic behavioural states. CTAP-treated mice remained in an aversive state, whereas DAMGO-treated mice displayed predominantly neutral behaviour.

CONCLUSIONS

Fear extinction requires the integrity of the µ-opioid system in the dorsal midline thalamus. Pharmacological stimulation of MOR and associated facilitation of fear extinction recall suggest a potential therapeutic avenue for stress-related or anxiety disorders.

Neuropeptide S promotes wakefulness through the inhibition of sleep-promoting ventrolateral preoptic nucleus neurons

STUDY OBJECTIVES

The regulation of sleep-wake cycles is crucial for the brain's health and cognitive skills. Among the various substances known to control behavioral states, intraventricular injection of neuropeptide S (NPS) has already been shown to promote wakefulness. However, the NPS signaling pathway remains elusive. In this study, we characterized the effects of NPS in the ventrolateral preoptic nucleus (VLPO) of the hypothalamus, one of the major brain structures regulating non-rapid eye movement (NREM) sleep.

METHODS

We combined polysomnographic recordings, vascular reactivity, and patch-clamp recordings in mice VLPO to determine the NPS mode of action.

RESULTS

We demonstrated that a local infusion of NPS bilaterally into the anterior hypothalamus (which includes the VLPO) significantly increases awakening and specifically decreases NREM sleep. Furthermore, we established that NPS application on acute brain slices induces strong and reversible tetrodotoxin (TTX)-sensitive constriction of blood vessels in the VLPO. This effect strongly suggests that the local neuronal network is downregulated in the presence of NPS. At the cellular level, we revealed by electrophysiological recordings and in situ hybridization that NPSR mRNAs are only expressed by non-Gal local GABAergic neurons, which are depolarized by the application of NPS. Simultaneously, we showed that NPS hyperpolarizes sleep-promoting neurons, which is associated with an increased frequency in their spontaneous IPSC inputs.

CONCLUSION

Altogether, our data reveal that NPS controls local neuronal activity in the VLPO. Following the depolarization of local GABAergic neurons, NPS indirectly provokes feed-forward inhibition onto sleep-promoting neurons, which translates into a decrease in NREM sleep to favor arousal.

Amygdala, neuropeptides, and chronic pain-related affective behaviors

Neuropeptides play important modulatory roles throughout the nervous system, functioning as direct effectors or as interacting partners with other neuropeptide and neurotransmitter systems. Limbic brain areas involved in learning, memory and emotions are particularly rich in neuropeptides. This review will focus on the amygdala, a limbic region that plays a key role in emotional-affective behaviors and pain modulation. The amygdala is comprised of different nuclei; the basolateral (BLA) and central (CeA) nuclei and in between, the intercalated cells (ITC), have been linked to pain-related functions. A wide range of neuropeptides are found in the amygdala, particularly in the CeA, but this review will discuss those neuropeptides that have been explored for their role in pain modulation. Calcitonin gene-related peptide (CGRP) is a key peptide in the afferent nociceptive pathway from the parabrachial area and mediates excitatory drive of CeA neurons. CeA neurons containing corticotropin releasing factor (CRF) and/or somatostatin (SOM) are a source of long-range projections and serve major output functions, but CRF also acts locally to excite neurons in the CeA and BLA. Neuropeptide S (NPS) is associated with inhibitory ITC neurons that gate amygdala output. Oxytocin and vasopressin exert opposite (inhibitory and excitatory, respectively) effects on amygdala output. The opioid system of mu, delta and kappa receptors (MOR, DOR, KOR) and their peptide ligands (β-endorphin, enkephalin, dynorphin) have complex and partially opposing effects on amygdala function. Neuropeptides therefore serve as valuable targets to regulate amygdala function in pain conditions. This article is part of the special issue on Neuropeptides.

Corticosterone Treatment and Incubation Time After Contextual Fear Conditioning Synergistically Induce Fear Memory Generalization in Neuropeptide S Receptor-Deficient Mice

Fear memory generalization is a learning mechanism that promotes flexible fear responses to novel situations. While fear generalization has adaptive value, overgeneralization of fear memory is a characteristic feature of the pathology of anxiety disorders. The neuropeptide S (NPS) receptor (NPSR) has been shown to be associated with anxiety disorders and has recently been identified as a promising target for treating anxiety disorders. Moreover, stress hormones play a role in regulating both physiological and pathological fear memories and might therefore also be involved in anxiety disorders. However, little is known about the interplay between stress hormone and the NPS system in the development of overgeneralized fear. Here, we hypothesize that NPSR-deficient mice with high corticosterone (CORT) levels during the fear memories consolidation are more prone to develop generalized fear. To address this hypothesis, NPSR-deficient mice were submitted to a contextual fear conditioning procedure. Immediately after conditioning, mice received CORT injections (2.5 or 5 mg/kg). One day and 1 month later, the mice were tested for the specificity and strength of their fear memory, their anxiety level, and their startle response. Moreover, CORT blood levels were monitored throughout the experiment. Using this protocol, a specific contextual fear memory was observed in all experimental groups, despite the 5-mg/kg CORT-treated NPSR-deficient mice. This group of mice showed a generalization of contextual fear memory and a decreased startle response, and the females of this group had significantly less body weight gain. These findings indicate that interplay between CORT and the NPS system during the consolidation of fear memories is critical for the generalization of contextual fear.

Animal models of post-traumatic stress disorder and novel treatment targets

Understanding the neurobiological basis of post-traumatic stress disorder (PTSD) is fundamental to accurately diagnose this neuropathology and offer appropriate treatment options to patients. The lack of pharmacological effects, too often observed with the most currently used drugs, the selective serotonin reuptake inhibitors (SSRIs), makes even more urgent the discovery of new pharmacological approaches. Reliable animal models of PTSD are difficult to establish because of the present limited understanding of the PTSD heterogeneity and of the influence of various environmental factors that trigger the disorder in humans. We summarize knowledge on the most frequently investigated animal models of PTSD, focusing on both their behavioral and neurobiological features. Most of them can reproduce not only behavioral endophenotypes, including anxiety-like behaviors or fear-related avoidance, but also neurobiological alterations, such as glucocorticoid receptor hypersensitivity or amygdala hyperactivity. Among the various models analyzed, we focus on the social isolation mouse model, which reproduces some deficits observed in humans with PTSD, such as abnormal neurosteroid biosynthesis, changes in GABAA receptor subunit expression and lack of pharmacological response to benzodiazepines. Neurosteroid biosynthesis and its interaction with the endocannabinoid system are altered in PTSD and are promising neuronal targets to discover novel PTSD agents. In this regard, we discuss pharmacological interventions and we highlight exciting new developments in the fields of research for novel reliable PTSD biomarkers that may enable precise diagnosis of the disorder and more successful pharmacological treatments for PTSD patients.

Association of NPSR1 gene variation and neural activity in patients with panic disorder and agoraphobia and healthy controls

•

Higher amygdala activation in T risk allele carriers during the perception of agoraphobia-specific stimuli

•

Amygdala activation correlated negatively trendwise with the trait neuroticism in healthy controls carrying A/A genotype

•

A diagnosis x genotype interaction as a trend in the inferior orbitofrontal cortex during the perception of agoraphobia-specific stimuli

Introduction

The neurobiological mechanisms behind panic disorder with agoraphobia (PD/AG) are not completely explored. The functional A/T single nucleotide polymorphism (SNP) rs324981 in the neuropeptide S receptor gene (NPSR1) has repeatedly been associated with panic disorder and might partly drive function respectively dysfunction of the neural “fear network”. We aimed to investigate whether the NPSR1 T risk allele was associated with malfunctioning in a fronto-limbic network during the anticipation and perception of agoraphobia-specific stimuli.

Method

121 patients with PD/AG and 77 healthy controls (HC) underwent functional magnetic resonance imaging (fMRI) using the disorder specific “Westphal-Paradigm”. It consists of neutral and agoraphobia-specific pictures, half of the pictures were cued to induce anticipatory anxiety.

Results

Risk allele carriers showed significantly higher amygdala activation during the perception of agoraphobia-specific stimuli than A/A homozygotes. A linear group x genotype interaction during the perception of agoraphobia-specific stimuli showed a strong trend towards significance. Patients with the one or two T alleles displayed the highest and HC with the A/A genotype the lowest activation in the inferior orbitofrontal cortex (iOFC).

Discussion

The study demonstrates an association of the NPSR1rs324981 genotype and the perception of agoraphobia-specific stimuli. These results support the assumption of a fronto-limbic dysfunction as an intermediate phenotype of PD/AG.

Making translation work: Harmonizing cross-species methodology in the behavioural neuroscience of Pavlovian fear conditioning

Translational neuroscience bridges insights from specific mechanisms in rodents to complex functions in humans and is key to advance our general understanding of central nervous function. A prime example of translational research is the study of cross-species mechanisms that underlie responding to learned threats, by employing Pavlovian fear conditioning protocols in rodents and humans. Hitherto, evidence for (and critique of) these cross-species comparisons in fear conditioning research was based on theoretical viewpoints. Here, we provide a perspective to substantiate these theoretical concepts with empirical considerations of cross-species methodology. This meta-research perspective is expected to foster cross-species comparability and reproducibility to ultimately facilitate successful transfer of results from basic science into clinical applications.

Animal Models of PTSD: The Socially Isolated Mouse and the Biomarker Role of Allopregnanolone

Post-traumatic stress disorder (PTSD) is a debilitating undertreated condition that affects 8%-13% of the general population and 20%-30% of military personnel. Currently, there are no specific medications that reduce PTSD symptoms or biomarkers that facilitate diagnosis, inform treatment selection or allow monitoring drug efficacy. PTSD animal models rely on stress-induced behavioral deficits that only partially reproduce PTSD neurobiology. PTSD heterogeneity, including comorbidity and symptoms overlap with other mental disorders, makes this attempt even more complicated. Allopregnanolone, a neurosteroid that positively, potently and allosterically modulates GABAA receptors and, by this mechanism, regulates emotional behaviors, is mainly synthesized in brain corticolimbic glutamatergic neurons. In PTSD patients, allopregnanolone down-regulation correlates with increased PTSD re-experiencing and comorbid depressive symptoms, CAPS-IV scores and Simms dysphoria cluster scores. In PTSD rodent models, including the socially isolated mouse, decrease in corticolimbic allopregnanolone biosynthesis is associated with enhanced contextual fear memory and impaired fear extinction. Allopregnanolone, its analogs or agents that stimulate its synthesis offer treatment approaches for facilitating fear extinction and, in general, for neuropsychopathologies characterized by a neurosteroid biosynthesis downregulation. The socially isolated mouse model reproduces several other deficits previously observed in PTSD patients, including altered GABAA receptor subunit subtypes and lack of benzodiazepines pharmacological efficacy. Transdiagnostic behavioral features, including expression of anxiety-like behavior, increased aggression, a behavioral component to reproduce behavioral traits of suicidal behavior in humans, as well as alcohol consumption are heightened in socially isolated rodents. Potentials for assessing novel biomarkers to predict, diagnose, and treat PTSD more efficiently are discussed in view of developing a precision medicine for improved PTSD pharmacological treatments.

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.

Mechanisms of fear learning and extinction: synaptic plasticity-fear memory connection

RATIONALE

The ability to memorize threat-associated cues and subsequently react to them, exhibiting escape or avoidance responses, is an essential, often life-saving behavioral mechanism that can be experimentally studied using the fear (threat) conditioning training paradigm. Presently, there is substantial evidence supporting the Synaptic Plasticity-Memory (SPM) hypothesis in relation to the mechanisms underlying the acquisition, retention, and extinction of conditioned fear memory.

OBJECTIVES

The purpose of this review article is to summarize findings supporting the SPM hypothesis in the context of conditioned fear control, applying the set of criteria and tests which were proposed as necessary to causally link lasting changes in synaptic transmission in corresponding neural circuits to fear memory acquisition and extinction with an emphasis on their pharmacological diversity.

RESULTS

The mechanisms of synaptic plasticity in fear circuits exhibit complex pharmacological profiles and satisfy all four SPM criteria-detectability, anterograde alteration, retrograde alteration, and mimicry.

CONCLUSION

The reviewed findings, accumulated over the last two decades, provide support for both necessity and sufficiency of synaptic plasticity in fear circuits for fear memory acquisition and retention, and, in part, for fear extinction, with the latter requiring additional experimental work.

Cortico-limbic pain mechanisms

Pain has a strong emotional component and is defined by its unpleasantness. Chronic pain represents a complex disorder with anxio-depressive symptoms and cognitive deficits. Underlying mechanisms are still not well understood but an important role for interactions between prefrontal cortical areas and subcortical limbic structures has emerged. Evidence from preclinical studies in the rodent brain suggests that neuroplastic changes in prefrontal (anterior cingulate, prelimbic and infralimbic) cortical and subcortical (amygdala and nucleus accumbens) brain areas and their interactions (corticolimbic circuitry) contribute to the complexity and persistence of pain and may be predetermining factors as has been proposed in recent human neuroimaging studies.

Association of NPSR1 rs324981 polymorphism and treatment response to antidepressants in Chinese Han population with generalized anxiety disorder

In previous studies, neuropeptide S (NPS) and its cognate receptor (NPSR) have been involved in the pathogenesis of anxiety disorders in previous studies. Here, we aimed to investigate the association of NPSR1 polymorphism with generalized anxiety disorder (GAD) and its treatment response in Chinese Han population. Three hundred and thirty seven patients and one hundred and seventy seven healthy controls were involved in our study for 8 weeks. Further, Hamilton Anxiety Scale (HAMA) was used to assess anxiety symptom at baseline and the 1st, 2nd, 4th, 8th week. And all participants were genotyped for NPSR1 (rs324981) variants by polymerase chain reaction. Using Repeated-measures analysis, it showed significant reduction on HAMA scores in patients treated with escitalopram (F = 1.03, P = 0.362) and venlafaxine (F = 0.27, P = 0.763) respectively through 8 weeks treatment. Additionally, patients with AA and TT homozygous genotypes treated with venlafaxine XR had a higher reduction of HAMA scores compared to AT heterozygotic carriers (F = 4.18, P = 0.004), while no significant differences were found in patients treated with escitalopram (F = 1.05, P = 0.383). Thus, our study provides preliminary evidence that NPSR1 AA and TT homozygous genotypes have better treatment responses to venlafaxine XR in Chinese GAD patients, but not to escitalopram. Further studies are needed to verify the observation.

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.

Brain region-dependent gene networks associated with selective breeding for increased voluntary wheel-running behavior

Mouse lines selectively bred for high voluntary wheel-running behavior are helpful models for uncovering gene networks associated with increased motivation for physical activity and other reward-dependent behaviors. The fact that multiple brain regions are hypothesized to contribute to distinct behavior components necessitates the simultaneous study of these regions. The goals of this study were to identify brain-region dependent and independent gene expression patterns, regulators, and networks associated with increased voluntary wheel-running behavior. The cerebellum and striatum from a high voluntary running line and a non-selected control line were compared. Neuropeptide genes annotated to reward-dependent processes including neuropeptide S receptor 1 (Npsr1), neuropeptide Y (Npy), and proprotein convertase subtilisin/kexin type 9 (Pcsk9), and genes implicated in motor coordination including vitamin D receptor (Vdr) and keratin, type I cytoskeletal 25 (Krt25) were among the genes exhibiting activity line-by-region interaction effects. Genes annotated to the Parkinson pathway presented consistent line patterns, albeit at different orders of magnitude between brain regions, suggesting some parallel events in response to selection for high voluntary activity. The comparison of gene networks between brain regions highlighted genes including transcription factor AP-2-delta (Tfap2d), distal-less homeobox 5 gene (Dlx5) and sine oculis homeobox homolog 3 (Six3) that exhibited line differential expression in one brain region and are associated with reward-dependent behaviors. Transcription factors including En2, Stat6 and Eomes predominated among regulators of genes that differed in expression between lines. Results from the simultaneous study of striatum and cerebellum confirm the necessity to study molecular mechanisms associated with voluntary activity and reward-dependent behaviors in consideration of brain region dependencies.

Novel transmitters in brain stem vagal neurocircuitry: new players on the pitch

The last few decades have seen a major increase in the number of neurotransmitters and neuropeptides recognized as playing a role in brain stem neurocircuits, including those involved in homeostatic functions such as stress responsiveness, gastrointestinal motility, feeding, and/or arousal/wakefulness. This minireview will focus on the known physiological role of three of these novel neuropeptides, i.e., apelin, nesfatin-1, and neuropeptide-S, with a special emphasis on their hypothetical roles in vagal signaling related to gastrointestinal motor functions.

Plasma Neuropeptide-S Levels in Populations Diagnosed with Generalized Anxiety Disorder: A Controlled Study

Introduction

Neuropeptide S (NPS) is a novel neuropeptide reported to be involved in fear-and stress-related conditions and their corresponding neuroendocrine processes. The aim of this study was to compare the plasma NPS levels in patients suffering from generalized anxiety disorder (GAD) and those of healthy controls.

Methods

A total of 40 subjects diagnosed with GAD and 40 healthy controls were recruited in the study. The Hamilton Anxiety Scale (HAM-A), Generalized Anxiety Disorder-7 (GAD-7), and Hamilton Depression Scale (HAM-D) were administered to all participants to determine the severity of participants' anxiety and concomitant depressive symptoms. The plasma NPS levels were measured from the fasting venous blood samples obtained from each participant.

Results

The median plasma NPS level was found to be significantly higher in the GAD group in comparison to the control group (28.8 pg/mL as against 19.1 pg/mL, p=0.01). A significant positive correlation was observed between the plasma NPS levels and HAM-A scores (rs=0.23, p=0.04) as well as the GAD-7 scores (rs=0.28, p=0.01). The p-value obtained from the correlation analysis between the plasma NPS levels and HAM-D scores was 0.052. A receiver operating characteristic (ROC) analysis revealed that the plasma NPS levels could enable the identification of GAD with 67.5% sensitivity and 62.5% specificity, when the cut-off value was determined as 25.06 pg/mL.

Conclusions

Our results support the view that plasma NPS levels, which has demonstrated anxiolytic effects on the central nervous system, is related to the severity of anxiety in GAD and could be considered as a candidate marker for the identification of GAD.