Neuropeptide S pathway in PTSD and neuropsychiatric disorders: A review
Beijing Institute of Pharmacology and Toxicology, Beijing, China
Department of Pharmacology, Hangzhou Normal University, Hangzhou, Zhejiang, China
Department of Pharmacy, Shenyang Pharmaceutical University, Shenyang, Liaoning, China
Department of Hematology, Zhejiang Provincial People’s Hospital and People’s Hospital of Hangzhou Medical College, Hangzhou, China
*Correspondence to Xiang-min Tong: tongxiangmin@163.com and Fei Li: lf5335317@163.comAbstract
Post-traumatic stress disorder (PTSD) is a multidimensional illness that seldom occurs alone: roughly 80% of patients also meet criteria for anxiety, depression, chronic pain, substance-use, eating or cognitive disorders. Converging genetic, neurochemical and behavioral findings implicate the neuropeptide S (NPS) system—acting through its G-protein-coupled NPS receptor (NPSR)—as a common regulator of these diverse phenotypes. This narrative review surveys studies published 2000–2024 in PubMed, Embase and Web of Science that examine NPS/NPSR involvement in core PTSD features and typical comorbidities. The functional rs324981 A/T polymorphism, which boosts NPSR surface expression and signaling, consistently associates with greater PTSD risk and symptom severity. In rodent models, exogenous NPS reduces anxiety- and fear-like behaviors, speeds fear-memory extinction, stabilizes the hypothalamic–pituitary–adrenal axis, enhances dopaminergic tone and elevates hippocampal brain-derived neurotrophic factor (BDNF)—changes concordant with symptom relief. Additional work shows that NPS lessens pain affect, dampens alcohol and opioid intake, eases withdrawal-induced anxiety and lowers food consumption, hinting at a multimodal therapeutic profile. These effects converge on limbic and mid-brain circuits (amygdala, ventral tegmental area, locus coeruleus, paraventricular nucleus) and engage oxytocinergic, adenosinergic and endocannabinoid pathways. Translation remains limited by NPS’s rapid degradation, poor blood–brain-barrier penetration and scarcity of brain-penetrant NPSR ligands, but advances in intranasal delivery, lipid-acylated analogs, biased NPSR agonists and “humanized” NPSR-variant models offer promising solutions. Collectively, current pre-clinical and genetic evidence positions the NPS–NPSR axis as a versatile therapeutic target for both core PTSD symptoms and their disabling comorbidities, warranting rigorous translational studies to refine mechanism, optimize drug-like properties and test clinical efficacy.
Introduction
Post-traumatic stress disorder (PTSD), also referred to as delayed psychogenic reactions, is a psychological condition resulting from exposure to significant trauma or catastrophic events. This disorder is characterized by delayed onset and can lead to enduring mental health issues. PTSD has emerged as a prevalent mental health concern, with incidence rates of approximately 6%–9% in the general population [1, 2]. However, among individuals who have experienced severe trauma—such as combat veterans, refugees, victims of assault, and those facing pandemic-related stressors—the prevalence may rise to approximately 25%. During the COVID-19 pandemic, studies indicated that between 15.8% and 35.6% of the U.S. population reported symptoms of PTSD [3], while 10.7% to 23.5% of frontline healthcare workers developed the disorder [4, 5]. Classic symptoms of PTSD primarily include the re-experiencing trauma, avoidance behaviors, negative emotions and thoughts, and hyperarousal. It is important to recognize that individuals exposed to complex traumatic events are not only at risk for developing PTSD but often exhibit comorbid conditions such as depression [6], anxiety [7], insomnia [8], cognitive impairment [9], chronic pain [10], substance abuse [11], and eating disorders [12]. Epidemiological studies indicate that approximately 80% of individuals with PTSD meet the criteria for at least one additional psychiatric diagnosis, including depression and substance use disorders [13]. Consequently, the treatment of PTSD can be particularly challenging, especially in the context of concurrent comorbidities. In recent years, significant attention has focused on the regulatory role of the endogenous substance neuropeptide S (NPS) within the central nervous system [14]. NPS is a polypeptide composed of 20 amino acids, exhibiting a highly conserved primary structure across vertebrate species. Its name derives from the presence of serine as the amino-terminal residue in NPS across various organisms [15]. The NPS receptor (NPSR), formerly designated as GPR154, functions as a double-coupled receptor linked to Gs and Gq proteins. When NPS binds to NPSR, it triggers the intracellular accumulation of cyclic adenosine monophosphate (cAMP) and facilitates the release of intracellular Ca2+, thereby activating the downstream mitogen-activated protein kinase signaling pathway [16].
The NPSR gene contains an A/T single nucleotide polymorphism (SNP rs324981) located at the 7P14 locus on chromosome 7, which results in an amino acid substitution (Asn107Ile) [17]. This mutation enhances the cell-surface expression of NPSR, rendering NPSR Ile107 approximately ten times more potent than NPSR Asn107, without affecting binding affinity [18, 19]. Haxhibeqiri et al. [20] demonstrated that the risk of PTSD is significantly elevated in homozygous T allele carriers compared to homozygous A allele carriers within the Balkan war population. Furthermore, NPSR rs324981 influences stress levels [21], the incidence of anxiety disorders [22, 23], alcohol use disorders (AUDs) [24], and cognitive impairments [25], all of which are comorbid symptoms of PTSD. Moreover, accumulating research indicates that NPS has the potential to alleviate PTSD-like behaviors, exert anxiolytic effects [26], diminish fear-related responses [27], improve learning and memory deficits [28], and regulate substance use disorders [29–31] (see Table 1). This body of evidence suggests that the NPS–NPSR system may play a critical role not only in the regulation of PTSD but also in related neuropsychiatric disorders.
| Animal | Active doses and route of administration | Symptoms | Experiments | Effects | Ref |
|---|---|---|---|---|---|
| SD rats | NPS (1.0 nmol/0.5 µL, intra-BLA) | PTSD-like behaviors | Predator scent stress, elevated plus maze, cut-off behavioral criteria model, acoustic startle response, freezing behavior | Alleviate the PTSD-like behaviors, including anxiety, freezing response, and hyperarousal | [36] |
| C57BL/6J | NPS (10 µM/0.5µL, intra-LA) | PTSD-like behaviors | Immobilization stress, elevated plus maze, fear conditioning | Alleviate anxiety, reduce conditioned fear responses | [38] |
| Wistar rats | NPS (1 nmol, i.c.v.) | Aggressive and anxiety behaviors | Resident-intruder test, elevated plus maze | Alleviate anxiety, reduce aggressive behavior | [41] |
| Swiss mice, NPSR(+/+) and NPSR(−/−) with CD-1 strain | NPS (0.01–1 nmol, i.c.v.) | Aggressive behaviors | Resident/intruder test | Reduce aggressive behavior | [42] |
| Wistar rats | NPS (0.05 and 0.5 nmol/side, intra-VTA) | _ | Locomotion | Increase locomotor activity | [59] |
| SD rats | NPS (1 nmol, i.c.v.) | Sleep deprivation and anxiety | Paradoxical sleep deprivation, open field test, light-dark box | Reduce paradoxical sleep deprivation induced anxiety-like behavior | [79] |
| NPSR(+/+)/NPSR(−/−) mice with 129S6 genetic background | NPS (0.1 nmol, i.c.v.) | Anxiety | Locomotor | Increase locomotor activity in NPSR(+/+) mice but not in NPSR(−/−) mice | [90] |
| NPSR (+/+)/NPSR(−/−) with CD-1 genetic background | NPS (1 nmol, i.c.v.) | Anxiety | Elevated plus maze, open field test | Alleviate anxiety in NPSR(+/+) mice but not in NPSR(−/−) mice | [91] |
| SD rats | NPS (10 nmol, i.c.v.) | Pain | Hot plate, tail flick | Prolong the hot plate latency but not tail flick latency | [102] |
| Swiss mice | NPS (0.1 nmol, i.c.v.) | Pain | Formalin test | Reduced formalin-induced nociception | [103] |
| C57BL/6J | NPS (0.3 and 1 nmol, i.c.v.) | Pain | Hot-plate test | Prolong the hot plate latency | [104] |
| Alcohol-preferring and non-preferring rats | NPS (0.075, 0.3, and 1.2 nmol, i.c.v.) | Substances use disorder | Alcohol preferences, elevated plus-maze | Reduced alcohol consumption in the alcohol-preferring rat | [107] |
| Alcohol-preferring and nonpreferring rats | NPS (0.1, 0.5, 1.0, and 2.0 nmol, i.c.v.) | Substances use disorder | Alcohol self-administration | Reduced alcohol self-administration | [108] |
| Wistar rats | NPS (1.0, 2.0, 4.0 nmol, i.c.v.) | Substances use disorder | Alcohol self-administration | Increase ethanol seeking elicited by ethanol-associated cues | [109] |
| Kunming strain mice | NPS (1, 3, 6 and 10 nmol, i.c.v.) | Substances use disorder | Conditioned place preference | Reduce the morphine-induced CPP acquisition and expression | [111] |
| C57BL/6 | NPS (1 nmol, i.c.v.) | Cognition deficit | Inhibitory avoidance, novel object recognition | Enhance memory retention, but not acquisition or recall | [120] |
| Kunming strain mice | NPS (1 nmol, i.c.v.) | Cognition deficit | Morris water maze | Facilitate spatial memory, mitigate spatial memory impairment | [121] |
| Adult male Wistar rats | NPS (1 nmol, i.c.v.)/Nasal NPS administration (40 nmol) | Cognition deficit | Elevated plus-maze, object discrimination, social discrimination | Reduce non-social anxiety, facilitate object discrimination but not social discrimination | [122] |
| C57BL/6 | Nasal NPS administration (10 µL of 1 mM solution) | Cognition deficit | T-Maze | Facilitate reversal learning without affecting the acquisition | [123] |
| Kunming strain mice | NPS (0.1 nmol, i.c.v.) | Food intake in fasted mice | Food intake in fasted mice | Inhibit food intake in fasted mice | [134] |
This review synthesizes evidence on the role of NPS–NPSR system in: (i) core PTSD symptoms, (ii) PTSD-associated neuropsychiatric syndromes, ultimately evaluating its potential as a multimodal therapeutic agent. We analyzed findings from studies published between 2000 and 2024, identified through systematic searches of PubMed, Embase, and Web of Science. The keywords employed included “PTSD,” “comorbidity,” “animal models,” “neuropeptide S,” “neuropeptide S receptor,” “single nucleotide polymorphism,” “anxiety,” “substance use disorder,” “pain,” “food intake,” “norepinephrine,” “dopamine,” and “hypothalamic–pituitary–adrenal axis” (HPA). We prioritized original research articles, reviews, and meta-analyses published in English, focusing on studies that investigate the role of NPS in modulating PTSD and related neuropsychiatric disorders. Studies that were irrelevant to the scope or had significant methodological limitations were excluded.
Role of NPS–NPSR system in PTSD
Anxiety, conditioned fear responses, fear memory disorders, and severe stress reactions are the primary characteristics of PTSD [32, 33]. An expanding body of literature underscores the role of the NPS system in regulating stress, mood, cognitive function, and anxiety. Multiple studies have highlighted the amygdala’s crucial involvement in PTSD [34]. Neuroimaging studies of patients with PTSD have revealed increased activation in the amygdala [35]. Exposure to predator-scent stress (PSS) induces PTSD-like behaviors in rats. Microinjection of NPS into the basolateral amygdala (BLA) has been demonstrated to alleviate anxiety, reduce the freezing response, and restore the diminished expression of brain-derived neurotrophic factor (BDNF) and neuropeptide Y Y1 receptor (NPY-Y1R) in the hippocampus in this model [36]. Ten days post-experience of acute immobilization stress, mice exhibited a significant increase in PTSD-like behaviors, characterized by heightened anxiety and fear responsiveness [37]. This increase could be mitigated by injecting NPS into the lateral amygdala (LA), while administration of NPSR antagonists exacerbated the symptoms [38]. Jiang et al. [39] reported a significant reduction in NPSR mRNA levels in the hypothalamus of mice subjected to a single prolonged stress (SPS) model, while NPS mRNA levels were significantly elevated compared to the control group. Additionally, the repeated social defeat stress (R-SDS) model serves as an effective animal model for studying PTSD [40]. Within this framework, i.c.v. infusion of NPS (1 nmol) was shown to reduce anxiety and aggressive behaviors in both low and high anxiety rats [41]. Moreover, in the resident-intruder test—another model for PTSD-like behavior [37]—resident mice lacking NPSR exhibited longer attack durations on intruder mice than wild-type (WT) counterparts. Administration of NPS (0.01 nmol–1 nmol, i.c.v.) significantly decreased the number of attacks and the total time spent attacking by resident mice [42]. These findings suggest that the NPS system plays a pivotal role in modulating behaviors associated with PTSD.
Possible mechanisms of NPS in PTSD
Norepinephrine (NE) plays a critical role in the body’s response to fear and anxiety. Symptoms of hyperawareness and irritability in patients with PTSD are associated with heightened NE activity [43]. Additionally, individuals with PTSD demonstrate increased cortisol and NE responses to stress [44, 45]. Clinically, the α1 receptor antagonist prazosin and the β receptor antagonist propranolol have shown potential in treating PTSD [43, 46]. Animal studies indicate that a single injection of isoproterenol, a nonselective β-adrenergic agonist, into the amygdala enhances the reconsolidation of fear memories, suggesting that elevated NE during fear memory processing may contribute to the persistence of traumatic memories [47]. NE is known to regulate the cAMP/PKA and CaMKII/PKC signaling pathways through the activation of β-adrenoceptors, which can result in PTSD-like memory impairments [47]. Giustino et al. [48] found that stress or activation of the locus coeruleus (LC)-NE pathway induces deficits in fear memory extinction. This effect is likely mediated by stress-induced increases in BLA activity, with intra-BLA administration of propranolol blocking the extinction deficits caused by LC-NE activation. Moreover, NE neurons in the LC have been found to express at least 19 neuropeptide transcripts [49]. NPS interacts with various neuromodulators, including NE [50]. Reports indicate that NPS inhibits NE release; specifically, Raiteri et al. [51] demonstrated that NPS selectively inhibits NE release through its action on noradrenergic nerve terminals within the frontal cortex. These findings suggest that NPS may reduce the activity of noradrenergic neurons by suppressing NE release, potentially aiding in the alleviation of fear memory reconsolidation and extinction. Dopamine (DA), the predominant catecholamine neurotransmitter in the brain, plays a crucial role in regulating various physiological processes, including reward, motivation, exercise, and emotion. Previous research indicates that dopaminergic dysfunction may directly contribute to impaired fear extinction, learning, and memory in patients with PTSD [52]. Animal studies have shown decreased DA levels in the medial prefrontal cortex (mPFC) and the BLA of rats following 18 days of exposure to traumatic stimuli in the SPS model [53]. Additionally, D2 receptors in the mPFC and BLA are implicated in fear extinction, as reduced receptor levels have been observed in rats during this process [54]. Notably, D1 receptor knockout mice do not exhibit fear memory in fear-conditioning experiments, suggesting the involvement of the dopaminergic system in fear learning and extinction [55]. Clinical studies have demonstrated that the DA receptor agonist kb220z significantly alleviates nightmare symptoms in PTSD patients [56]. Preclinical investigations have also revealed that DA receptor D2/D3 agonists, such as rotigotine and pramipexole, can diminish PTSD-like symptoms in experimental models [57]. NPS has been reported to enhance DA release, with i.c.v. administration of NPS leading to a dose-dependent increase in DA release in the rat mPFC [58]. Furthermore, microinjection of NPS into the ventral tegmental area (VTA) of rats has been shown to elevate locomotor activity and DA metabolites in the nucleus accumbens (NAc) [59]. Although the mechanisms of NPS in PTSD remain uninvestigated, these findings suggest that NPS may target the DA system to exert a potential anti-PTSD effect by increasing DA levels.
The HPA axis is a neuroendocrine system that regulates the body’s response to stress [60]. Key neuroendocrine hormones involved in the HPA axis include corticotropin-releasing hormone, adrenocorticotropic hormone, and cortisol [61]. Research indicates a strong association between HPA axis dysregulation and PTSD [62]. Numerous studies have documented this dysregulation in individuals with PTSD, characterized by increased sensitivity of the HPA feedback system, reduced cortisol levels, and diminished urinary cortisol excretion. These alterations contribute to symptoms such as fatigue and mood disturbances [63]. Animal research indicates that on the 18th day post-exposure to stress in the rat post-stress susceptibility (PSS) model, there is a significant reduction in basal corticosterone pulse amplitude and a dampened corticosterone response to stressors. This suggests that impairment in the corticosterone response may serve as a susceptibility or risk factor for the development of PTSD [64]. Furthermore, the administration of corticosterone to rats one hour after trauma stimulation diminishes fear memory retrieval and facilitates the extinction of fear memories in PTSD models [65, 66]. Elevated in vivo release of NPS in the amygdala has been observed following local depolarization and emotional stress [67]. Administration of NPS activates the HPA axis, resulting in the release of corticotropin-releasing hormone, adrenocorticotropic hormone, and corticosterone [68]. This cascade of hormonal events may play a critical role in the modulation of stress and anxiety by NPS [68, 69]. These findings suggest that targeting the modulation of the HPA axis through NPS may represent a promising approach for PTSD treatment. BDNF is the most prevalent neurotrophic factor in the body. Upon binding to its specific receptor, Tropomyosin-related kinase receptor B (TrkB), BDNF plays a crucial role in modulating synaptic plasticity, neuronal survival, and apoptosis [70]. Disruptions in the BDNF-TrkB signaling pathway may significantly impact PTSD [71]. In the hippocampus, impaired conditional-fear learning and extinction have been linked to the absence of BDNF-TrkB signaling in key regions, including the ventromedial prefrontal cortex (PFC), anterior cingulate cortex, and NAc [72]. Clinical studies have demonstrated a substantial reduction in BDNF levels in the blood of PTSD patients compared to healthy individuals, indicating its potential as a diagnostic biomarker for PTSD [73]. In the SPS rat model, a significant reduction in cerebrospinal fluid BDNF levels has been observed [74]. Furthermore, the administration of BDNF (1 mmol, 10 mmol, 30 mmol, i.c.v.) in this model has been demonstrated to dose-dependently increase the time spent in the central area relative to the total time in the open field test [74]. Additionally, research indicates that BDNF expression is decreased following PSS exposure but is enhanced after NPS microinjection into the BLA [36], suggesting that NPS may regulate neuronal plasticity and other functions through the modulation of BDNF.
Conclusion
NPS–NPSR system plays a potential impact on PTSD and its associated disorder, including anxiety, fear, learning and memory, substances use disorder, eating disorders and pain (Table 1). These effects are mediated by various brain regions (Figure 1) and mechanisms (Figure 2). Based on current preclinical evidence from animal studies, NPSR may serve as a potential target for modulating PTSD responses, offering novel insights into the neural mechanisms underlying PTSD.
However, since the regulatory effects of NPS on neuropsychiatric disorders are exclusively derived from evidence in animal experiments, it remains uncertain whether NPS exerts regulatory effects on PTSD in humans. Therefore, it is necessary to employ animal models with higher validity that can reflect PTSD and its comorbidities to investigate the role of NPS. Concurrently, further research is required to elucidate the mechanisms underlying the actions of NPS and NPSR in PTSD and its comorbidities, such as the molecular and neural circuit mechanisms through which NPSR modulates DA, NE, and the HPA axis in PTSD models.
Limited tools have hindered understanding of the NPS pathway. In recent years, however, techniques such as fluorescent neuromodulator sensors, electrochemical sensors, and in vivo microdialysis coupled with mass spectrometry enable real-time monitoring of fluctuations in neuropeptide release presence. Similarly, tools like photoactivatable neuropeptides and genetically encoded biosensors derived from specific nanobodies provided precise spatial and temporal resolution of G protein-coupled receptor (GPCR) activation and inactivation [128], The development of these technologies is accelerating research progress into targeting the NPS–NPSR system for PTSD therapeutic applications.
In addition, regarding NPS, its clinical application is limited by poor metabolic stability and the inability to cross the blood–brain barrier (BBB). Researchers have explored alternative delivery methods, such as nasal administration instead of ventricular injection [137], and developed lipid acylation-modified NPS-palmitic acid self-assembled coupling formulations, which demonstrate effective penetration ability and potential pharmacological effects [138]. Thus, further efforts are warranted to develop optimized delivery systems for NPS. Furthermore, it is imperative to conduct further research targeting NPSR to develop NPSR agonists and antagonists capable of crossing the BBB. In recent years, researchers have rationally designed NPSR agonists exhibiting biased signaling properties. RTI-263, a biased NPSR agonist, demonstrates NPS-like anxiogenic-like effects and memory-enhancing effects in preclinical models. Crucially, and distinct from NPS, RTI-263 significantly attenuates cue-induced reinstatement of cocaine seeking in rats [139]. Thus, the functional benefits conferred by biased NPSR agonists provide a direction for targeting NPSR in the therapeutic development for PTSD.
Additionally, SNP rs324981 play a crucial role in the regulatory effects of the NPS–NPSR system. Therefore, utilizing an NPSR mutant “humanized” animal model is essential to explore the biological and pharmacological effects of NPS in PTSD [140, 141]. This approach could provide valuable insights for developing precise therapeutic strategies for PTSD based on the modulation of the NPS–NPSR system.