The cerebellum is a structure in the suprasegmental nervous system classically known for its involvement in motor functions such as motor planning, coordination, and motor learning. However, with scientific advances, other functions of the cerebellum, such as cognitive, emotional, and autonomic processing, have been discovered. Currently, there is a body of evidence demonstrating the involvement of the cerebellum in nociception and pain processing. The aim of this review is to present the current literature on the anatomical, physiological, and functional aspects of the cerebellum in pain processing and suggest functional mechanisms of pain processing based on the cerebellum and its connections with other brain structures. To achieve this, searches were conducted in databases to identify relevant studies on the topic. Studies with relevant data and information were collected and summarized. Current literature demonstrates that the cerebellum receives nociceptive afferents from different pathways and exhibits activity in different regions including the vermis, hemispheres, and deep cerebellar nuclei in pain processing. Through its connections with different brain regions, it is possible that the cerebellum participates in the multidimensional processing of pain, which may make it a potential therapeutic target for pain treatment.

The complex nature of pain pathophysiology complicates the establishment of objective diagnostic criteria and targeted treatments. The heterogeneous manifestations of pain stemming from various primary diseases contribute to the complexity and diversity of underlying mechanisms, leading to challenges in treatment efficacy and undesirable side effects. Recent evidence suggests the presence of apoptotic cells at injury sites, the distal dorsal root ganglia (DRG), spinal cord, and certain brain regions, indicating a potential link between the ineffective clearance of dead cells and debris and pain persistence. This review highlights recent research findings indicating that efferocytosis plays a significant yet often overlooked role in lesion expansion while also representing a potentially reversible impairment that could be targeted therapeutically to mitigate chronic pain progression. We examine recent advances into how efferocytosis, a process by which phagocytes clear apoptotic cells without triggering inflammation, influences pain initiation and intensity in both human diseases and animal models. This review summarizes that efferocytosis contributes to pain progression from the perspective of defective and inefficient efferocytosis and its subsequent secondary necrocytosis, cascade inflammatory response, and the shift of phenotypic plasticity and metabolism. Additionally, we investigate the roles of newly discovered genetic alterations or modifications in biological signaling pathways in pain development and chronicity, providing insights into innovative treatment strategies that modulate efferocytosis, which are promising candidates and potential avenues for further research in pain management and prevention.

Neuropathic pain is a prevalent and debilitating condition experienced by the majority of individuals with spinal cord injury (SCI). The complex pathophysiology of neuropathic pain, involving continuous activation of microglia and astrocytes, reactive gliosis, and altered neuronal plasticity, poses significant challenges for effective treatment. This review focuses on the pivotal roles of microglia and astrocytes, the two major glial cell types in the central nervous system, in the development and maintenance of neuropathic pain after SCI. We highlight the extensive bidirectional interactions between these cells, mediated by the release of inflammatory mediators, neurotransmitters, and neurotrophic factors, which contribute to the amplification of pain signaling. Understanding the microglia-astrocyte crosstalk and its impact on neuronal function is crucial for developing novel therapeutic strategies targeting neuropathic pain. In addition, this review discusses the fundamental biology, post-injury pain roles, and therapeutic prospects of microglia and astrocytes in neuropathic pain after SCI and elucidates the specific signaling pathways involved. We also speculated that the extracellular matrix (ECM) can affect the glial cells as well. Furthermore, we also mentioned potential targeted therapies, challenges, and progress in clinical trials, as well as new biomarkers and therapeutic targets. Finally, other relevant cell interactions in neuropathic pain and the role of glial cells in other neuropathic pain conditions have been discussed. This review serves as a comprehensive resource for further investigations into the microglia-astrocyte interaction and the detailed mechanisms of neuropathic pain after SCI, with the aim of improving therapeutic efficacy.

Lysophosphatidylinositol (LPI) is an endogenous signaling molecule for the GPR55 receptor. Previous studies have shown that arachidonoyl-lysophosphatidylinositol (LPI-20:4) produced an increase in the inflammatory mediators NLPR3 (inflammasome-3 marker) and IL-1b in neurons from both rat dorsal root ganglion (DRG) and hippocampal cultures. Because LPI is comprised of a family of lipid structures that vary in fatty acyl composition, the current work examined neuroinflammatory responses to various LPI structures in DRG and hippocampal cultures as assessed by high-content fluorescent imaging. Major endogenous LPI fatty acyl structures consisting of 16:0, 18:0, 18:1, or 20:4 were compared for their effects on IL-1b, NLRP3, and GPR55 immunoreactive areas of neurites and cell bodies after a 6-h treatment. Among these four LPI structures, only LPI-20:4 treatment produced increases in immunoreactive areas for GPR55, NLRP3, and IL-1b in DRG and hippocampal neurites. In contrast, all other LPI structures tested produced a decrease in all of these inflammatory immunoreactive areas in both neurites and cell bodies. Additional studies with LPI-20:4 treatment indicated that IL-6, IL-18, and TNF-α were significantly increased in neurites of DRG and hippocampal cultures. However, oleoyl-lysophosphatidylinositol (LPI-18:1) treatment produced decreases in these three cytokines. Using the viability dye Alamar blue, LPI-20:4 was shown to produce concentration-dependent decreases, whereas all other endogenous LPI structures produced increases with this assay. These studies indicate that fatty acyl structure is the major determinant of LPI for neuroinflammatory responses in DRG and hippocampal cultures, with LPI-20:4 showing pro-inflammatory effects and all other endogenous LPIs tested exhibiting anti-inflammatory responses.

Chronic pancreatitis (CP) is a fibroinflammatory disease, with pain as its most prominent symptom. This article provides a comprehensive review of the pathophysiology, assessment methodologies, and management strategies pertaining to pain in CP. Pathophysiological mechanisms include inflammatory and neuropathic components, including peripheral and central sensitization. Pain assessment can include unidimensional and multidimensional pain assessment scales, neurophysiological assessments, and advanced imaging techniques. Management strategies include a spectrum from lifestyle modifications, pharmacologic interventions, and interventional procedures to neuromodulatory techniques and other experimental treatments.

Chronic neuropathic pain is a debilitating neuroplastic disorder that notably impacts the quality of life of millions of people worldwide. This complex condition, encompassing various manifestations, such as sciatica, diabetic neuropathy and postherpetic neuralgia, arises from nerve damage or malfunctions in pain processing pathways and involves various biological, physiological and psychological processes. Maladaptive neuroplasticity, known as central sensitization, plays a critical role in the persistence of chronic neuropathic pain. Current treatments for neuropathic pain include pharmacological interventions (for example, antidepressants and anticonvulsants), invasive procedures (for example, deep brain stimulation) and physical therapies. However, these approaches often have limitations and potential side effects. In light of these challenges, interest in noninvasive neuromodulation techniques as alternatives or complementary treatments for neuropathic pain is increasing. These methods aim to induce analgesia while reversing maladaptive plastic changes, offering potential advantages over conventional pharmacological practices and invasive methods. Recent technological advancements have spurred the exploration of noninvasive neuromodulation therapies, such as repetitive transcranial magnetic stimulation, transcranial direct current stimulation and transcranial ultrasound stimulation, as well as innovative transformations of invasive techniques into noninvasive methods at both the preclinical and clinical levels. Here this review aims to critically examine the mechanisms of maladaptive neuroplasticity in chronic neuropathic pain and evaluate the efficacy of noninvasive neuromodulation techniques in pain relief. By focusing on optimizing these techniques, we can better assess their short-term and long-term effects, refine treatment variables and ultimately improve the quality of neuropathic pain management.

Recurrent acute pancreatitis (RAP) poses significant clinical challenges, with 32.3% developing to chronic pancreatitis within 5 years. The underlying microbial factors contributing to RAP remain poorly understood. This study aims to identify blood microbial signatures associated with RAP and explore the potential microbial predictors for RAP.

In this prospective cohort, 90 acute pancreatitis patients are classified into non-recurrent acute pancreatitis (NRAP, n=68) and RAP (n=22) groups based on the number of pancreatitis episodes. Microbial composition of blood samples is analyzed using 5-region (5R) 16S rRNA gene sequencing. Key microbial taxa and functional predictions are made. A random forest model is used to assess the predictive value of microbial features for RAP. The impact of Staphylococcus hominis (S. hominis) on RAP is further evaluated in an experimental mouse model.

Linear discriminant analysis effect size (LEfSe) analysis highlights significant microbial differences, with Paracoccus aminovorans, Corynebacterium glucuronolyticum and S. hominis being prominent in RAP. Functional predictions indicate enrichment of metabolic pathways in the RAP group. Random forest analysis identifies key microbial taxa with an AUC value of 0.759 for predicting RAP. Experimental validation shows that S. hominis exacerbates pancreatic inflammation in mice.

This study identifies distinct clinical and microbial features associated with RAP, emphasizing the role of specific bacterial taxa in pancreatitis recurrence. The findings suggest that microbial profiling could enhance the diagnosis and management of RAP, paving the way for personalized therapeutic approaches.

Chronic pain affects over 20% of the global population and contributes to the vast burden of psychiatric illness. While effective treatments for chronic pain remain limited, both alcohol and cannabis have been used for centuries to manage pain and closely associated negative affective symptoms. However, persistent misuse of alcohol and/or cannabis in such a negative reinforcement fashion is hypothesized to increase the risk of severity of substance use disorders (SUDs). The current review describes neurobiological evidence for the analgesic efficacy of alcohol and primary cannabis constituents and how use or co-use of these substances may influence SUD risk.

Parvalbumin-positive (PV+) interneurons (basket and chandelier cells) regulate the firing rate of pyramidal neurons in the cerebral cortex and play a key role in the generation of network oscillations in the cerebral cortex. A growing body of evidence suggest that cortical PV+ interneurons become overactive in chronic pain and contribute to nociceptive sensitization by inhibiting a top-down analgesic pathway. Here, we provide further support to this hypothesis showing that intracortical infusion of the GABAA receptor antagonist, bicuculline, caused analgesia in a mouse model of chronic inflammatory pain, although it reduced pain thresholds in healthy mice. We propose that mGlu5 metabotropic glutamate receptors and perineuronal nets (PNNs) shape the activity of PV+ interneurons in chronic pain, generating a form of maladaptive plasticity that enhances behavioural pain responses. mGlu5 receptors might be locally targeted by drugs activated by light delivered in cortical regions of the pain matrix, whereas the density of PNNs enwrapping PV+ interneurons might be reduced by local activation of PNN-degrading enzyme, such as type-9 matrix metalloproteinase. These strategies, which may require invasive treatments, might be beneficial in the management of severe pain which is refractory to conventional pharmacological and non-pharmacological interventions.

Chronic pain is a prevalent condition in companion animals and poses significant welfare challenges. To address these concerns effectively, veterinary clinicians must have a comprehensive understanding of the neuroanatomy of nociception and the intricate processes underlying pain perception. This knowledge is essential for planning and implementing targeted treatment strategies. However, much of the existing information on pain mechanisms is derived from studies on rodents or humans, highlighting the need for further translational research to bridge this gap for veterinary applications. This review aims to provide veterinary clinicians with an in-depth overview of the spinal nociceptive pathways in the dog and cat, tracing the journey from nociceptor activation to cortical processing in the brain. Additionally, the review explores factors influencing nociceptive signaling and pain perception. By enhancing the understanding of these fundamental physiological processes, this work seeks to lay the groundwork for developing effective therapies to manage the complexities of chronic pain in companion animals.

Postherpetic neuralgia (PHN) is a debilitating condition resulting from herpes zoster infection, characterized by persistent pain that significantly impacts quality of life. This study aimed to investigate the white matter microstructural alterations associated with PHN and to assess the relationship between diffusion metrics and clinical symptoms.

A total of 29 patients with PHN, 28 patients recovering from herpes zoster (RHZ), and 27 healthy controls (HC) were recruited, and clinical assessments were obtained to evaluate pain intensity and psychological distress. Diffusion tensor imaging (DTI) data was collected, followed by analysis of diffusion and neurite orientation dispersion and density imaging (NODDI) metrics. Statistical analyses included ANOVA to compare groups and Pearson correlation coefficients to assess relationships between imaging metrics and clinical outcomes.

PHN patients exhibited significantly altered white matter integrity, specifically in neurite density index (NDI) and orientation dispersion index, compared to both RHZ patients and HC. Significant correlations were also found between altered imaging metrics and clinical assessments of pain and emotional distress, with lower fractional anisotropy (FA) and NDI associated with higher pain scores and psychological symptoms.

Our study highlights significant microstructural changes in white matter tracts in patients with PHN, indicating compromised neural integrity that correlates with increased pain perception and emotional distress. NODDI demonstrated superior sensitivity in detecting these alterations compared to traditional DTI metrics, underscoring its potential for enhancing diagnostic and therapeutic approaches in managing chronic pain conditions like PHN.

To explore the changes in the white matter microstructure of the ascending pain conduction pathways in patients with chronic neck and shoulder pain (CNSP) using combined brain and spinal cord diffusion tensor imaging techniques, and to assess its correlation with clinical indicators and cognitive functions.

A 3.0T MRI scanner was used to perform combined brain and spinal cord diffusion tensor imaging scans on 31 CNSP patients and 24 healthy controls (HCs), extracting the spinothalamic tract (STT) and quantitatively analyzing the fractional anisotropy (FA) and mean diffusivity (MD) which reflect the microstructural integrity of nerve fibers. Additionally, these differences were subjected to partial correlation analysis in relation to Visual Analog Scale (VAS) scores, duration of pain, Self-Rating Anxiety Scale (SAS), and Self-Rating Depression Scale (SDS).

Compared to HCs, CNSP patients showed decreased mean FA values and increased mean MD values in bilateral intracranial STT compared to the HC group, but two-sample t-test results indicated no statistically significant differences (p > 0.05). FA values of the left STT (C2 segment, C5 segment) and right STT (C1 segment, C2 segment) were significantly decreased in bilateral cervical STTs of CNSP patients; MD values of the left STT (C1 segment, C2 segment, C5 segment) and right STT (C1 segment, C5 segment) were significantly increased (p < 0.05). Partial correlation analysis results showed that FA values of STT in CNSP patients were negatively correlated with VAS scores, duration of pain, SAS scores, and SDS scores, while MD values were positively correlated with VAS scores and duration of pain (Bonferroni p < 0.05).

This research identified that patients with CNSP exhibited reduced mean FA and increased mean MD in the bilateral intracranial STT, although these differences were not statistically significant (p > 0.05). Conversely, significant abnormalities were observed in specific segments of the bilateral cervical STT (p < 0.05), which were also correlated with variations in pain intensity, illness duration, and levels of anxiety and depression. These findings contribute a novel neuroimaging perspective to the evaluation and elucidation of the pathophysiological mechanisms underlying chronic pain in the ascending conduction pathways.

Chronic pain after surgery, also known as chronic postsurgical pain (CPSP), is recognized as a significant public health issue with serious medical and economic consequences. Current research on CPSP underscores the significant roles of both peripheral and central sensitization in pain development and maintenance. Peripheral sensitization occurs at the site of injury, through the hyperexcitability of nerve fibers due to surgical damage and the release of inflammatory mediators. This leads to increased expression of pronociceptive ion channels and receptors, such as transient receptor potential and acid-sensing ion channels (ASIC), enhancing pain signal transmission. Central sensitization involves long-term changes in the central nervous system, particularly in the spinal cord. In this context, sensitized spinal neurons become more responsive to pain signals, driven by continuous nociceptive input from the periphery, which results in an enhanced pain response characterized by hyperalgesia and/or allodynia. Key players in this process include N-methyl-D-aspartate receptor and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors, along with proinflammatory cytokines and chemokines released by activated glia. These glial cells release substances that further increase neuronal excitability, maintaining the sensitized state and contributing to persistent pain. The activation of antinociceptive systems is required for the resolution of pain after surgery, and default in these systems may also be considered as an important component of CPSP. In this review, we will examine the clinical factors underlying CPSP in patients and the mechanisms previously established in preclinical models of CPSP that may explain how acute postoperative pain may transform into chronic pain in patients.

Chronic postsurgical pain (CPSP) is a common adverse outcome following surgical procedures. Despite ongoing research, the risk factors and effective strategies for mitigating CPSP remain uncertain. Regional anesthesia is a potentially beneficial yet debated intervention for mitigating the risk of CPSP. This review will delve into the mechanistic aspects of regional anesthesia and critically assess the current literature to provide a thorough understanding of its role and effectiveness. The incidence and severity of CPSP are linked to nerve damage, neuroplastic changes and immunological responses. Although numerous mechanisms contributing to CPSP have been identified, translational research is sparse, and findings are often inconsistent. Evidence suggests that regional anesthetic techniques could have a role in reducing CPSP risk across various clinical scenarios. Techniques studied include wound infiltration, peripheral nerve blocks, fascial plane blocks, thoracic paravertebral blocks and epidural anesthesia. Current data indicate that epidural anesthesia might decrease CPSP risk following thoracotomy, wound infiltration may be effective after major breast surgery and cesarean delivery, and serratus anterior plane block or pectoralis/interpectoral plane blocks might be beneficial in breast surgery. However, the existing evidence is limited and marked by several constraints especially the multifactorial causes, underscoring the need for further research in this area.

Degenerative joint disease (DJD) occurs very commonly in cats and can be associated with pain. Almost 70% of cats with DJD-associated pain suffer the co-morbidity of chronic kidney disease (CKD). There are currently very limited treatment or management options. A greater understanding of the systems biology of DJD, DJD-associated pain, and CKD may contribute to identifying disease specific biomarkers and relevant targets for the development of therapeutics for the control of these conditions in cats, and help inform human pain therapeutic development.

Using mass spectrometry-based proteomic profiling of the serum of 200 highly phenotyped cats with varying burdens of DJD, pain, and CKD, we identified significant individual proteins and pathways.

Functional pathway analysis, based on differentially abundant proteins across individual disease states (DJD, pain, CKD), identified pathways playing a role in DJD and DJD-associated pain including acute phase response signaling, LXR/RXR and FXR/RXR activation and the complement system. With the added co-morbidity of CKD, similar pathways were identified, with the addition of IL-12 signaling and production in macrophages.

We identified differentially abundant proteins associated with DJD, pain and CKD and future work should evaluate these proteins as potential biomarkers of disease (individually or as clusters). Further, these data could be leveraged to identify novel therapeutic targets to address the gap in our ability to manage DJD, pain, and CKD in cats. Given that our work was in cats with naturally occurring DJD, these results may have translational applicability to human health.

The role of the complement system in pain syndromes has garnered attention on the back of preclinical and clinical evidence supporting its potential as a target for new analgesic pharmacotherapies. Of the components that make up the complement system, component 5a (C5a) and component 3a (C3a) are most strongly and consistently associated with pain. Receptors for C5a are widely found in immune resident cells (microglia, astrocytes, sensory neuron-associated macrophages (sNAMs)) in the central nervous system (CNS) as well as hematogenous immune cells (mast cells, macrophages, T-lymphocytes, etc.). When active, as is often observed in chronic pain conditions, these cells produce various inflammatory mediators including pro-inflammatory cytokines. These events can trigger nervous tissue inflammation (neuroinflammation) which coexists with and potentially maintains peripheral and central sensitization. C5a has a likely critical role in initiating this process highlighting its potential as a promising non-opioid target for treating pain. This review summarizes the most up-to-date research on the role of the complement system in pain with emphasis on the C5 pathway in peripheral tissue, dorsal root ganglia (DRG) and the CNS, and explores advances in complement-targeted drug development and sex differences. A perspective on the optimal application of different C5a inhibitors for different types (e.g., neuropathic, post-surgical and chemotherapy-induced pain, osteoarthritis pain) and stages (e.g., acute, subacute, chronic) of pain is also provided to help guide future clinical trials. PERSPECTIVE: This review highlights the role and mechanisms of complement components and their receptors in physiological and pathological pain. The potential of complement-targeted therapeutics for the treatment of chronic pain is also explored with a focus on C5a inhibitors to help guide future clinical trials.

Temporomandibular disorders (TMDs) are prevalent conditions affecting the temporomandibular joint (TMJ), masticatory muscles, and associated structures, leading to pain, restricted movement, and joint noises. These disorders are multifactorial in origin, involving structural, functional, and psychological components. This review delves into the neurophysiological mechanisms of pain perception in TMDs, focusing on peripheral and central processes, including the role of neural plasticity in chronic pain. Peripheral mechanisms involve nociceptors in the TMJ, activated by inflammatory mediators, mechanical stress, and tissue damage, leading to pain. Peripheral sensitization, driven by factors such as cytokines and neuropeptides, enhances nociceptor sensitivity, contributing to chronic pain states. The trigeminal nerve is pivotal in transmitting nociceptive information to the central nervous system (CNS), with C-fibers and A-delta fibers involved in pain perception. Central sensitization, a hallmark of chronic pain in TMDs, involves neuroplastic changes in the CNS, including wind-up and long-term potentiation (LTP), enhancing pain perception and facilitating pain persistence. Neuroplasticity, both central and peripheral, plays a critical role in the development of chronic pain. Central plasticity includes synaptic changes and alterations in brain connectivity, which were observed in functional imaging studies of TMD patients. Peripheral plasticity involves the upregulation of ion channels and neurotransmitters, sustaining pain signals. Additionally, neuroimmune interactions between microglia, astrocytes, and pain pathways are integral to central sensitization. Understanding these mechanisms is crucial for developing effective treatments targeting both peripheral and central pain processes. Emerging therapies, including transient receptor potential (TRP) channel blockers and neuroimmune modulators, offer new avenues for managing TMD pain, emphasizing the need for a multifaceted treatment approach.

The central sensitization inventory (CSI) is a questionnaire that has been widely used as a tool for assessing symptoms associated with sensitization. However, its ability to identify individuals with this phenomenon has recently been questioned. The aim of this study was to assess the correlation of CSI with psychosocial and psychophysical factors in patients with painful TMD diagnosed according to diagnostic criteria for temporomandibular disorders (DC/TMD) and asymptomatic controls, as well as to determine the influence of these variables on the CSI scores variations.

This cross-sectional study with 77 patients diagnosed with painful TMD according to DC/TMD and 101 asymptomatic controls realized correlations between CSI, WUR, PPT, CPM and psychosocial questionnaires (HADS, PSQI, PCS and PSS). In cases where significant correlations existed, the potential influence of these variables on CSI variation was explored through linear regression analysis.

It has been found that the CSI correlates with psychosocial variables (anxiety, depression, catastrophizing, sleep and stress) (p < 0.0006) regardless of the presence of TMD, and that 68.9% of the variation in CSI scores can be influenced by all these variables (except stress). On the contrary, the CSI does not correlate with psychophysical parameters indicative of pain amplification (wind-up ratio and conditioned pain modulation) (p > 0.320).

CSI is more associated with psychosocial factors than with more robust indicators of probable central sensitization (CS), thus limiting its utility in detecting this phenomenon both in TMD patients and healthy individuals.

The research highlights a noteworthy relationship between the central sensitization inventory and psychological factors, emphasizing their substantial influence on inventory values. This correlation offers crucial insights into mental health markers within the questionnaire. Additionally, the lack of connection with pain amplification implies a necessary re-evaluation of the inventory's diagnostic suitability, especially in cases of painful temporomandibular disorders. Thus, caution is urged in its application for identifying CS in these individuals.

Spinal cord stimulation (SCS) is an effective modality for pain treatment, yet its underlying mechanisms remain elusive. Neurokinin 1 receptor-positive (NK1R + ) neurons in spinal lamina I play a pivotal role in pain transmission. To enhance our mechanistic understanding of SCS-induced analgesia, we investigated how different SCS paradigms modulate the activation of NK1R + neurons, by developing NK1R-Cre;GCaMP6s transgenic mice and using in vivo calcium imaging of superficial NK1R + neurons under anesthesia (1.5% isoflurane). Neurokinin 1 receptor-positive neurons in the lumbar spinal cord (L4-5) showed a greater activation by electrical test stimulation (TS, 3.0 mA, 1 Hz) at the hindpaw at 2 weeks after tibia-sparing nerve injury (SNI-t) than in naïve mice. Spinal cord stimulation was then delivered through a bipolar plate electrode placed epidurally at L1-2 level. The short-term 50-Hz high-intensity SCS (80% motor threshold [MoT], 10 minutes) induced robust and prolonged inhibition of NK1R + neuronal responses to TS in both naïve and SNI-t mice. The 30-minute 50-Hz and 900-Hz SCS applied at moderate intensity (50% MoT) also significantly inhibited neuronal responses in SNI-t mice. However, at low intensity (20% MoT), the 30-minute 900-Hz SCS only induced persistent neuronal inhibition in naïve mice, but not in SNI-t mice. In conclusion, both 10-minute high-intensity SCS and 30-minute SCS at moderate intensity inhibit the activation of superficial NK1R + neurons, potentially attenuating spinal nociceptive transmission. Furthermore, in vivo calcium imaging of NK1R + neurons provides a new approach for exploring the spinal neuronal mechanisms of pain inhibition by neuromodulation pain therapies.

Migraine is a complex neurovascular disorder whose pathogenesis involves activation of the trigeminal vascular system, central and peripheral sensitization, and neuroinflammation. Calcitonin gene-related peptide (CGRP) plays a dominant role and activation of MAPK and NF-κB signaling pathways regulates neuropeptide release, glial cell activation, and amplification of nociceptive signals. Aberrant activation of these pathways drives migraine onset and chronicity. The ubiquitin-proteasome system (UPS) is involved in neurological and inflammatory disorders. ubiquitination in the UPS is achieved through a cascade of enzymes, including Ub-activating enzyme (E1), Ub-coupling enzyme (E2), and Ub-ligase (E3). The aim of this review is to systematically explore the role of ubiquitination in the regulation of MAPK and NF-κB signaling pathways, with a focus on the mechanisms of ubiquitinating enzymes in neuroinflammation and pain signal amplification, and to explore their potential as diagnostics, biomarkers, predictors of response to therapy, and monitoring of chronicity in migraine disease.

Neuropathic pain poses a significant clinical challenge, largely due to the incomplete understanding of its molecular mechanisms, particularly the role of mitochondrial dysfunction. Bioinformatics analysis revealed that pyroptosis and inflammatory responses induced by spared nerve injury (SNI) in the spinal dorsal horn play a critical role in the initiation and persistence of neuropathic pain. Among the factors involved, TSPO (translocator protein) emerged as a key regulator. Our experimental findings showed that TSPO expression was upregulated during neuropathic pain, accompanied by mitochondrial dysfunction, specifically manifested as impaired mitochondrial biogenesis, disrupted mitochondrial dynamics (including insufficient expression of mitochondrial biogenesis and fusion-related proteins, as well as significantly increased expression of fission-related proteins), and activation of pyroptosis. Pharmacological upregulation of TSPO, but not its downregulation, effectively alleviated SNI-induced pain hypersensitivity, improving mitochondrial function and reducing pyroptosis. Immunofluorescence staining confirmed that TSPO was primarily localized in astrocytes, and its expression mirrored the protective effects on mitochondrial health and pyroptosis prevention. PCR array analysis suggested a strong association between TSPO and the mitochondrial regulation pathway AMPK-PGC-1α. Notably, inhibition of AMPK-PGC-1α abolished TSPO effects on mitochondrial balance and pyroptosis suppression. Furthermore, Mendelian randomization analysis of GWAS data indicated that increased TSPO expression was linked to pain relief. Through drug screening, molecular docking, and behavioral assays, we identified zopiclone as a promising TSPO-targeting drug for pain treatment. In summary, this study enhances our understanding of the molecular interplay between TSPO, mitochondrial health, and neuropathic pain, highlighting TSPO as a potential therapeutic target for pain management.

Microglia play a crucial role in monitoring the microenvironment of the central nervous system. Over the past decade, the role of microglia in the field of pain has gradually been unraveled. Microglia activation not only releases proinflammatory factors that enhance nociceptive signaling, but also participates in the resolving of pain. Opioids induce microglia activation, which enhances phagocytic activity and release of neurotoxic substances. Conversely, microglia activation reduces opioid efficacy and results in opioid tolerance. The application of microglia research to clinical pain management and drug development is a promising but challenging area. Microglia-targeted therapies may provide new avenues for pain management.

Endometriosis is an inflammatory disease associated with chronic pelvic pain (CPP). Growing evidence indicates that endometriotic lesions are not the sole source of pain. Instead, central nervous system (CNS) dysfunction created by prolonged peripheral and central sensitization plays a role in developing endometriosis-associated CPP. This study investigated how CPP is established using a multiple lesion induction mouse model of endometriosis, as repeated retrograde menstruation is considered underlying endometriosis pathogenesis.

We generated endometriosis-like lesions by injecting endometrial tissue fragments into the peritoneal cavity in mice. The mice received a single (1x) or multiple inductions (6x) to simulate recurrent retrograde menstruation. Lesion development, hyperalgesia by behavioral testing, signs of peripheral sensitization, chronic inflammation, and neuroinflammation were examined with lesions, peritoneal fluids, dorsal root ganglia (DRG), spinal codes, and brain.

Multiple lesion inductions increased lesion numbers and elevated abdominal and hind paw hypersensitivity compared to single induction mice. Elevated persistent glial cell activation across several brain regions and/or spinal cords was found in the multiple induction mice. Specifically, IBA1+ microglial soma size was increased in the hippocampus and thalamus. IBA1+ cells were abundant in the cortex, hippocampus, thalamus, and hypothalamus of the multiple induction mice. GFAP+ astrocytes were mainly elevated in the hippocampus. Elevated TRPV1, SP, and CGRP expressions in the DRG were persistent in the multiple induction mice. Furthermore, multiple inductions induced the severe disappearance of TIM4hi MHCIIlo residential macrophages and the influx of increased proinflammatory TIM4lo MHCIIhi macrophages in the peritoneal cavity. The single and multiple inductions elevated secreted TNFα, IL-1β, and IL-6 levels in the peritoneal cavity at 2 weeks. Elevated cytokine levels returned to the pre-induction levels in the single induction mice at 6 weeks; however, they remained elevated in the multiple induction mice.

Our results indicate that the repeatedly occurring lesion inductions (=mimic retrograde menstruation) can be a peripheral stimulus that induces nociceptive pain and creates composite chronic inflammatory stimuli to cause neuroinflammation and sensitize the CNS. The circuits of neuroplasticity and stimulation of peripheral organs via a feedback loop of neuroinflammation may mediate widespread endometriosis-associated CPP.

Children's clinical pain phenotypes are complex, and there is a lack of objective biological diagnostic markers and cognitive patterns. Detecting physiological signals through wearable devices simplifies disease diagnosis and holds the potential for remote medical applications.

This research established a pain recognition model based on AI skin potential (SP) signal analysis. A total of 237 subjects participated in this study, comprising 152 boys and 85 girls, ranging in age from 2 to 16 years old. Initially, we preprocessed SP signals and built datasets for pain and non-pain conditions, including 195 pain and 97 non-pain samples. Then, we applied wavelet transform (WT) to capture the time-frequency characteristics of the signals and extract energy features and created a feature set comprising 30 features and selected 10 most relevant ones using the "SelectKBest" function.We compared six algorithms, optimized their parameters, and evaluated the stability and fitting performance of each algorithm. The random forest (RF) algorithm emerged as the best, demonstrating significant performance in pain recognition with an accuracy of 80.3 % and a sensitivity of 92 %. The SP signals generated by children of different genders, ages, and needling positions during indwelling needle puncture were accurately recognized.

We developed a comprehensive SP recognition model, innovatively employing WT for SP signal analysis. This time-frequency analysis method, by preserving low-frequency features, is particularly suitable for SP signals. By combining pain monitoring with SP signals and ML, subjective pain experiences are transformed into quantifiable data, achieving high accuracy and real-time measurement capabilities. These advantages provide valuable technical support for clinical pediatric pain management.

Lysophosphatidylinositol (LPI) is an endogenous signaling molecule for the GPR55 receptor. Previous studies have shown that arachidonoyl-lysophosphatidylinositol (LPI-20:4) produced an increase in the inflammatory mediators NLPR3 (inflammasome - 3 marker) and IL-1b in neurons from both rat dorsal root ganglion (DRG) and hippocampal cultures. Because LPI is comprised of a family of lipid structures that vary in fatty acyl composition, the current work examined neuroinflammatory responses to various LPI structures in DRG and hippocampal cultures as assessed by high content fluorescent imaging. Major endogenous LPI fatty acyl structures consisting of 16:0, 18:0, 18:1 or 20:4 were compared for their effects on IL-1b, NLRP3 and GPR55 immunoreactive areas of neurites and cell bodies after a 6-hour treatment. Among these four LPI structures, only LPI-20:4 treatment produced increases in immunoreactive areas for GPR55, NLRP3 and IL-1b in DRG and hippocampal neurites. In contrast, all other LPI structures tested produced a decrease in all of these inflammatory immunoreactive areas in both neurites and cell bodies. Additional studies with LPI-20:4 treatment indicated that IL-6, IL-18 and TNF-a were significantly increased in neurites of DRG and hippocampal cultures. However, oleoyl-lysophosphatidylinositol (LPI-18:1) treatment produced decreases in these three cytokines. Using the viability dye alamar blue, LPI-20:4 was shown to produce concentration-dependent decreases, whereas all other endogenous LPI structures produced increases with this assay. These studies indicate that fatty acyl structure is the major determinant of LPI for neuroinflammatory responses in DRG and hippocampal cultures, with LPI-20:4 showing pro-inflammatory effects and all other endogenous LPIs tested exhibited anti-inflammatory responses.

To investigate differences in the microstructure of the spinothalamic tract (STT) white matter in people with chronic neck and shoulder pain (CNSP) using diffusion tensor imaging, and to assess its correlation with pain intensity and duration of the pain.

A 3.0T MRI scanner was used to perform diffusion tensor imaging scans on 31 people with CNSP and 24 healthy controls (HCs), employing the Automatic Fiber Segmentation and Quantification (AFQ) method to extract the STT and quantitatively analyze the fractional anisotropy (FA) and mean diffusivity (MD), reflecting the microstructural integrity of nerve fibers. Correlations of these differences with duration of pain and visual analog scale (VAS) scores were analyzed.

No significant differences in the mean FA or MD values of the bilateral STT were observed between people with CNSP and HCs (p > 0.05), as indicated by the two-sample t test. Further point-by-point comparison along 100 equidistant nodes within the STT pathway revealed significant reductions in FA values in the left (segments 12-18, 81-89) and right (segments 9-19, 76-80) STT in the CNSP group compared to HCs; significant increases in MD values were observed in the left (segments 1-13, 26-30, 71-91) and right (segments 8-17, 76-91) STT (p < 0.05, FWE corrected). Partial correlation analysis indicates that in people with CNSP, the FA values of the STT in regions with damaged white matter structure show a negative correlation with VAS scores and duration of pain, whereas MD values show a positive correlation with VAS scores and duration of pain.

This study found that people with CNSP exhibit white matter microstructural abnormalities in the specific segments of STT. These abnormalities are associated with the patient's pain intensity and disease duration. The findings offer a new neuroimaging perspective on the pathophysiological basis of chronic pain in the ascending conduction process and its potential role in developing targeted intervention strategies. However, due to the limited sample size and the lack of statistical significance when analyzing the entire spinothalamic tract, these conclusions should be interpreted with caution. Further research with larger cohorts is necessary to validate these results.

Temporomandibular joint osteoarthritis (TMJOA) is a severe form of temporomandibular joint disorders (TMD), and orofacial inflammatory allodynia is one of its common symptoms which lacks effective treatment. N-methyl-D-aspartate receptor (NMDAR), particularly its subtypes GluN2A and GluN2B, along with gap junctions (GJs), are key players in the mediation of inflammatory pain. However, the precise regulatory mechanisms of GluN2A, GluN2B, and GJs in orofacial inflammatory allodynia during TMJ inflammation still remain unclear. Here, we established the TMJ inflammation model by injecting Complete Freund's adjuvant (CFA) into the TMJ and used Cre/loxp site-specific recombination system to conditionally knock out (CKO) GluN2A and GluN2B in the trigeminal ganglion (TG). Von-frey test results indicated that CFA-induced mechanical allodynia in the TMJ region was relieved in GluN2A and GluN2B deficient mice. In vivo, CFA significantly up-regulated the expression of GluN2A and GluN2B, Gjb1, Gjb2, Gjc2 and Panx3 in the TG, and GluN2A and GluN2B CKO played different roles in mediating the expression of Gjb1, Gjb2, Gjc2 and Panx3. In vitro, NMDA up-regulated the expression of Gjb1, Gjb2, Gjc2 and Panx3 in satellite glial cells (SGCs) as well as promoted the intercellular communication between SGCs, and GluN2A and GluN2B knocking down (KD) altered the expression and function differently. NMDAR regulated Gjb1 and Panx3 through ERK1/2 pathway, and mediated Gjb2 and Gjc2 through MAPK, PKA, and PKC intracellular signaling pathways. These findings shed light on the distinct functions of GluN2A and GluN2B in mediating peripheral sensitization induced by TMJ inflammation in the TG, offering potential therapeutic targets for managing orofacial inflammatory allodynia.

The current opioid crisis urgently calls for developing non-addictive pain medications. Progress has been slow, highlighting the need to uncover targets with unique mechanisms of action. Extracellular adenosine alleviates pain by activating the adenosine A1 receptor (A1R). However, efforts to develop A1R agonists have faced obstacles. The equilibrative nucleoside transporter subtype 1 (ENT1) plays a crucial role in regulating adenosine levels across cell membranes. We postulate that ENT1 inhibition may enhance extracellular adenosine levels, potentiating endogenous adenosine action at A1R and leading to analgesic effects. Here, we modify the ENT1 inhibitor dilazep based on its complex X-ray structure and show that this modified inhibitor reduces neuropathic and inflammatory pain in animal models while dilazep does not. Notably, our ENT1 inhibitor surpasses gabapentin in analgesic efficacy in a neuropathic pain model. Additionally, our inhibitor exhibits less cardiac side effect than dilazep via systemic administration and shows no side effects via local/intrathecal administration. ENT1 is colocalized with A1R in mouse and human dorsal root ganglia, and the analgesic effect of our inhibitor is linked to A1R. Our studies reveal ENT1 as a therapeutic target for analgesia, highlighting the promise of rationally designed ENT1 inhibitors for non-opioid pain medications.

Endometriosis is an inflammatory chronic condition associated with nociceptive, neuropathic, and nociplastic pain. Central sensitization (CS) is the primary nociplastic pain mechanism. However, there are currently no standardized methods for detecting CS or nociplastic pain. This review aims to identify available tools for characterizing CS/nociplastic pain in endometriosis-related chronic pelvic pain. Following the PRISMA-P protocol, MEDLINE, Embase, Scopus, and PsychINFO databases were searched on 23 April 2024, for the terms "endometriosis", "central sensitization", "nociplastic pain", "widespread pain", and "assessment tools". Publications were selected if they mentioned tool(s) for detecting nociplastic pain or CS in endometriosis patients. Information was extracted on study demographics, assessment types, and the tools used for detection. Of the 379 citations retrieved, 30 papers met the inclusion criteria. When working to identify CS and nociplastic pain, fourteen studies exclusively used patient-reported questionnaires, six used quantitative sensory testing (QST), two used clinical assessments, and eight used multiple approaches combining patient-reported questionnaires and clinical assessment. This review illustrates the diversity of tools currently used to identify CS and nociplastic pain in endometriosis patients. Further research is needed to evaluate their validity and to standardize methods in order to improve the accuracy of nociplastic pain identification and guide treatment.

Blast neurotrauma has been linked to impairments in higher-order cognitive functions, including memory, attention, and mood. Current literature is limited to a single overpressure exposure or repeated exposures at the same level of overpressure. In this study, a rodent model of primary blast neurotrauma was employed to determine the pressure at which acute and chronic neurological alterations occurred. Three pressure magnitudes (low, moderate and high) were used to evaluate injury thresholds. A biology shock tube (BST) was used to simulate shock waves with overpressures of 60 kPa, 90 kPa and 120 kPa respectively. Neurological behavior of the rats was assessed by the Multi-Conditioning System (MCS) at 1 d, 7 d, 28 d and 90 d after shock wave exposure. Serum dopamine (DA), 5-hydroxytryptamine (5-HT), brain-derived neurotrophic factor (BDNF) and gamma-aminobutyric acid (GABA) were measured at the same time points. The proteomic analysis was conducted to identify potentially vulnerable cellular and molecule targets of serum in the immediate post-exposure period. Results revealed that: (1) Anxiety-like behavior increased significantly at 1 d post-exposure in the medium and high overpressure (90 kPa, 120 kPa) groups, returned to baseline at 7 days, and anxiety-like behavior in the high overpressure groups re-emerged at 28 d and 90 d. (2) High overpressure (120 kPa) impaired learning and memory in the immediate post-exposure period. (3) The serum DA levels decreased significantly at 1 d post-exposure in the medium and high overpressure groups; The 5-HT levels decreased significantly at 1 d and 90 d in the high overpressure groups; The BDNF levels decreased significantly at 90 d in the high overpressure groups. (4) Proteomic analysis identified 38, 306, and 57 differentially expressed proteins in serum following low, medium and high overpressure exposures, respectively. Two co-expressed proteins were validated. Functional analysis revealed significant enrichment of 1121, 2096, and 1121 Gene Ontology (GO) items and 33, 47, and 26 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, indicating extensive molecular responses to overpressure in the early phase. These findings suggest that exposure, even at moderate levels, can induce persistent neurobehavioral and molecular alterations, highlighting the need for further research into the long-term consequences of blast neurotrauma.

Endometriosis affects 5% to 10% of reproductive age women and may be associated with severely painful and debilitating symptoms as well as infertility. Endometriosis involves hormonal fluctuations, angiogenesis, neurogenesis, vascular changes and neuroinflammatory processes. The neuroinflammatory component of endometriosis makes it a systemic disorder, similar to other chronic epithelial inflammatory conditions.

Inflammatory mediators, mast cells, macrophages, and glial cells play a role in endometriosis which can result in peripheral sensitization and central sensitization. There is overlap between chronic pelvic pain and endometriosis, but the two conditions are distinct. Effective treatment is based on a personalized approach using a variety of pharmacologic and other treatment options.

Hormonal therapies are a first-line approach, but endometriosis is a challenging condition to manage. 'Add-back' hormonal therapy has been effective. Painful symptoms are likely caused by the interplay of multiple factors and there may be a neuropathic component. Analgesics and anticonvulsants may be appropriate. A holistic approach and multimodal treatments are likely to be most effective. In addition to pharmacologic treatment, there are surgical and alternative medicine options. Endometriosis may also have a psychological component.

Capsaicin-containing red pepper sauce suspension augments esophageal contraction amplitude on conventional manometry. This study used high-resolution manometry (HRM) to investigate if capsaicin infusion modulates segmental esophageal smooth muscle peristalsis in healthy adults.

Sixteen healthy volunteers (mean age 37 years, 14 male) underwent HRM for the evaluation of primary peristalsis and secondary peristalsis using slow and rapid air distensions. Both primary and secondary peristalsis were assessed following infusions of capsaicin-containing red pepper sauce and saline.

Capsaicin infusion significantly increased heartburn symptoms compared to saline infusion (p < 0.001), and significantly decreased threshold volumes of secondary peristalsis during rapid air distensions (p = 0.02). The frequency of secondary peristalsis during rapid air distensions was significantly increased by capsaicin infusion (p = 0.03). Neither capsaicin infusion (p = 0.06) nor saline infusion (p = 0.27) altered threshold volume during slow air distensions. Capsaicin infusion significantly increased distal contractile integral (DCI) of primary peristalsis (p = 0.04), particularly in the proximal smooth muscle segment (p = 0.048). It enhanced secondary peristalsis during rapid air distensions (p = 0.003) but not during slow air distension (p = 0.23). Saline infusion significantly increased DCI of secondary peristalsis during rapid air distension (p = 0.01).

Augmentation of distension-induced secondary peristalsis can be modulated by activation of capsaicin-sensitive afferents similar to mechanosensitive afferents. Capsaicin-induced augmentation of primary peristalsis isolates to the cholinergic-mediated proximal smooth muscle segment, which warrants study in ineffective esophageal motility to determine therapeutic potential.

Recent research has demonstrated that chronic pain, resulting from peripheral nerve injury, leads to various symptoms, including not only allodynia and hyperalgesia but also anxiety, depression, and cognitive impairment. These symptoms are believed to arise due to alterations in gene expression and neural function, mediated by epigenetic changes in chromatin structure. Emerging evidence suggests that acupuncture can modulate DNA methylation within the central nervous system, contributing to pain relief and the mitigation of comorbidities. Specifically, acupuncture has been shown to adjust the DNA methylation of genes related to mitochondrial dysfunction, oxidative phosphorylation, and inflammation pathways within cortical regions, such as the prefrontal cortex, anterior cingulate cortex, and primary somatosensory cortex. In addition, it influences the DNA methylation of genes associated with neurogenesis in hippocampal neurons. This evidence indicates that acupuncture, a treatment with fewer side effects compared with conventional medications, could offer an effective strategy for pain management.

Medications currently used to treat pain are frequently associated with serious adverse effects and rapid development of tolerance. Thus, there is a need to develop more effective, and safer medicines for the population. Blocking NMDA receptors (NMDAR) has shown to be a promising target for the development of new drugs. That statement is due to NMDAR activation and glutamate release in the spinal cord which affects chronic pain modulation. Therefore, the aim of this study was to evaluate the possible spinal antinociceptive activity of PnTx4(5-5) toxin. The peptide is purified from the venom of the spider P. nigriventer and its affinity for NMDAR and sodium channels Nav1.2-1.6 has already been established.

We compared its effect and safety with MK-801 (NMDAR antagonist) and evaluated its influence on glutamate and reactive oxygen species (ROS) levels in CSF. PnTx4(5-5) was administered intrathecally in the Formalin test and co-administered with NMDA in the Spontaneous pain test. After three minutes of observation, mice cerebrospinal fluid was collected to measure glutamate and ROS levels.

The spider peptide inhibited nociception as post-treatment in the inflammatory phase of the Formalin test. Furthermore, it inhibited spontaneous nociception induced by NMDA, being more potent and effective than MK-801 in both models tested. A glutamate rise level in the CSF of mice was significantly reduced by the toxin, but ROS increase was not affected. The animals' motor skills were not affected by the tested doses of NMDAR inhibitors.

In conclusion, the results suggest PnTx4(5-5) may mediate its antinociceptive effect in the spinal cord not only by inhibiting postsynaptic receptors but probably also by acting on autoreceptors. This effect does not affect the motricity of mice at the highest dose tested, which suggests that it has therapeutic potential and safety for use as a painkiller.

Pain serves as a vital innate defense mechanism that can significantly impact an individual's quality of life. Understanding the physiological effects of pain well plays an important role in developing novel pain treatments. Nociceptor neurons play a key role in pain and inflammation. Interactions between nociceptors and the immune system occur both at the site of injury and within the central nervous system. Modulating chemical mediators and nociceptor activity offers promising new approaches to pain management. Essentially, the sensory nervous system is essential for modulating the body's protective response, making it critical to understand these interactions to discover new pain treatment strategies. New innovations in neuromodulation have led to alternatives to opioids individuals with chronic pain with consequent improvement in disease-based treatment and nerve targeting. New neural targets from cellular and structural perspectives have revolutionized the field of neuromodulation. This narrative review aims to elucidate the mechanisms of pain transmission and processing, examine the characteristics and properties of nociceptors, and explore how the immune system influences pain perception. It further provides an updated overview of the physiology of pain and neuromodulatory mechanisms essential for managing acute and chronic pain. We assess the current understanding of different pain types, focusing on key molecules involved in each type and their physiological effects. Additionally, we compare painful and painless neuropathies and discuss the neuroimmune interactions involved in pain manifestation.

Nociceptors, crucial sensory receptors within biological systems, are essential for survival in diverse and potentially hazardous environments. Efforts to replicate nociceptors through advanced electronic devices, such as memristors and neuromorphic transistors, have achieved limited success, capturing basic nociceptive functions while more advanced characteristics like various forms of central sensitization and analgesic effect remain out of reach. Here, we introduce a vertical multigate, multichannel electrolyte-gated transistor (Vm-EGT), designed to mimic nociceptors. Utilizing the hybrid mechanism combining electric-double-layer (EDL) with ion intercalation/deintercalation in EGTs, our approach successfully replicates peripheral sensitization and desensitization characteristics of nociceptors. The intricate multigate and multichannel design of the Vm-EGT enables the emulation of more advanced nociceptive functionalities, including central sensitization and analgesic effect. Furthermore, we demonstrate that by exploiting the inherent current-voltage relationship, the Vm-EGT can simulate these advanced nociceptive features and seamlessly transition between them. Integrating a Vm-EGT with a thermistor and a heating plate, we have developed an artificial thermal nociceptor that closely mirrors the sensory attributes of its biological counterpart. Our approach significantly advances the emulation of nociceptors, providing a basis for the development of sophisticated artificial sensory systems and intelligent robotics.

Patients with tissue inflammation or injury often experience aberrant mechanical pain hypersensitivity, one of leading symptoms in clinic. Despite this, the molecular mechanisms underlying mechanical distortion are poorly understood. Canonical transient receptor potential (TRPC) channels confer sensitivity to mechanical stimulation. TRPC3 and TRPC6 proteins, coassembling as heterotetrameric channels, are highly expressed in sensory neurons. However, how these channels mediate mechanical pain hypersensitivity has remained elusive. It is shown that in mice and human, TRPC3 and TRPC6 are upregulated in DRG and spinal dorsal horn under pathological states. Double knockout of TRPC3/6 blunts mechanical pain hypersensitivity, largely by decreasing nociceptor hyperexcitability and spinal synaptic potentiation via presynaptic mechanism. In corroboration with this, nociceptor-specific ablation of TRPC3/6 produces comparable pain relief. Mechanistic analysis reveals that upon peripheral inflammation, TRPC3/6 in primary sensory neurons get recruited via released bradykinin acting on B1/B2 receptors, facilitating BDNF secretion from spinal nociceptor terminals, which in turn potentiates synaptic transmission through TRPC3/6 and eventually results in mechanical pain hypersensitivity. Antagonizing TRPC3/6 in DRG relieves mechanical pain hypersensitivity in mice and nociceptor hyperexcitability in human. Thus, TRPC3/6 in nociceptors is crucially involved in pain plasticity and constitutes a promising therapeutic target against mechanical pain hypersensitivity with minor side effects.

Local anesthetic infiltration at the surgical site has been studied in various surgical disciplines; however, its impact on deep inferior epigastric artery perforator (DIEP) flap breast reconstruction has not been previously assessed. This study aimed to evaluate the effects of multiple intramuscular ropivacaine injections on donor site pain during DIEP flap breast reconstruction.

The study included 65 patients who received local ropivacaine injections during DIEP reconstructions between March 2022 and February 2023, compared to 55 patients who underwent surgeries without ropivacaine from October 2018 to July 2020. A total of 20 cc of 0.75% ropivacaine solution was evenly administered at 20 sites along the abdominal wall muscles. The effect of intramuscular ropivacaine injection on postoperative visual analog scale (VAS) was evaluated using linear mixed-effect model. Opioid consumption and hospital days were also compared.

The daily median VAS score was lower in the ropivacaine group (all p-values < 0.001). When analyzed using a linear mixed-effects model, those who received ropivacaine had significantly lower VAS scores over the first 5 days postoperatively (p-value < 0.001). The rate of VAS score decline was also faster in the ropivacaine group over the first 24 h postoperative (p-value = 0.045). Although opioid consumption was comparable between the groups, those receiving ropivacaine had significantly shorter hospital stay (p-value = 0.001) and no complications related to the injections were observed.

Multiple intramuscular injections of ropivacaine to the donor site may reduce postoperative pain and shorten hospital stays, without increasing opioid consumption.