Nociceptors: Their Role in Body’s Defenses, Tissue Specific Variations and Anatomical Update

The Role of TNF-α in Neuropathic Pain: An Immunotherapeutic Perspective

TNF-α is a pro-inflammatory cytokine that plays a pivotal role in the regulation of immune responses. It is predominantly produced by activated macrophages, although other cell types, such as T lymphocytes and NK cells, also contribute to its secretion. TNF-α participates in various physiological processes, including cell proliferation and differentiation. Moreover, TNF-α has been implicated in the pathogenesis of numerous inflammatory and autoimmune disorders. Recent studies have highlighted the important role of TNF-α in neuropathic pain, a complex and frequently disabling condition caused by nerve injury or dysfunction. Increased TNF-α levels in the nervous system have been associated with the onset of neuropathic pain, contributing to neuronal sensitization and alterations in pain signaling pathways. This study supports the idea that TNF-α connects the immune system with the nervous system, thereby supporting our understanding of the neuroimmune interface of pain and bringing a potential treatment against neuropathic pain: targeting TNF-α. Anti-TNF-α antibody administration reduces pain behaviors and neuroinflammation in preclinical animal models. Simultaneously, clinical trials are evaluating the safety and efficacy of anti-TNF-α treatments, with preliminary results indicating promising outcomes in patients experiencing neuropathic pain. Here, targeting TNF-α goes beyond its conventional spectrum of inflammatory pathologies and initiates a new mechanism-based approach to defining neuropathic pain, thereby improving the quality of life of the individuals affected and bringing together an area of colossal unmet clinical need.

Therapeutic components of acupuncture stimulation based on characteristics of sensory nerve and nervous signaling pathway

Acupuncture, a therapeutic practice rooted in traditional Chinese medicine and integrated with modern neuroscience, achieves its effects by stimulating sensory nerves at specific anatomical points known as acupoints. This review systematically explores the therapeutic components of acupuncture, emphasizing the interplay between sensory nerve characteristics and neural signaling pathways. Key factors such as acupoint location, needling depth, stimulation intensity, retention time, and the induction of sensations (e.g., Deqi) are analyzed for their roles in neural activation and clinical outcomes. The review highlights how variations in spinal segment targeting, tissue-specific receptor activation, and stimulation modalities (e.g., manual acupuncture, electroacupuncture, moxibustion) influence therapeutic effects. Emerging evidence underscores the significance of ion channels, dermatomes, myotomes, and gene-specific pathways in mediating systemic effects. Additionally, the differential roles of mechanical, thermal and nociceptive stimuli and the temporal dynamics of sensory and immune responses are addressed. While insights from animal models have advanced our understanding, their translation to clinical practice requires further investigation. This comprehensive review identifies critical parameters for optimizing acupuncture therapy, advocating for individualized treatment strategies informed by neuroanatomical and neurophysiological principles, ultimately enhancing its precision and efficacy in modern medicine. Please cite this article as: Wie HS, Kim SN. Therapeutic components of acupuncture stimulation based on characteristics of sensory nerve and nervous signaling pathway. J Integr Med. 2025; 23(2): 106-112.

Implications of nociceptor receptors and immune modulation: emerging therapeutic targets for autoimmune diseases

Chronic painful autoimmune disorders such as multiple sclerosis (MS), inflammatory bowel disease (IBD), and rheumatoid arthritis (RA) induce significant discomfort. They are defined by persistent inflammation and immune-mediated tissue injury. The activation and sensitisation of nociceptors, mutated in various disorders, are fundamental components contributing to the pain experienced in these conditions. Recent discoveries indicate that immunological mediators and nociceptive receptors interact functionally within peripheral and central sensitisation pathways, amplifying chronic pain. This research examines the involvement of nociceptors in rheumatoid arthritis, multiple sclerosis, and inflammatory bowel disease. It explores how immune cells and pro-inflammatory cytokines induce, sensitise and regulate various nociceptive receptors (P2X, TRPA1 and TRPV1). Finally, we address possible future directions with respect to the treatment of long-lasting effects on immunity, and what new drug targets could be pursued as well, in order to counteract such either neuro-immune interactions in conditions involving the immunological system. By studying nociceptive mechanisms across autoimmune illnesses, we want to identify shared pathways and activation of nociceptors specific to individual diseases. This will shed insight on potential therapies for managing pain associated with autoimmune diseases.

Spontaneous Pain and Pain Sensitivity in Response to Prolonged Experimental Sleep Disturbances-Potential Sex Differences

INTRODUCTION

Insomnia is a highly prevalent condition that predisposes individuals to many chronic pain disorders, with most of them showing pronounced sexual dimorphism. We investigated whether experimental insomnia-like sleep disturbances (ESD) affect spontaneous pain and pain sensitivity, and whether sex modulates pain responses.

METHODS

Twenty-four healthy participants (50% females, age 28.3 ± 5.9 years) participated in a study consisting of two 19-day in-laboratory protocols-an ESD protocol consisting of repeated nights of short and disrupted sleep with intermittent nights of undisturbed sleep and a control sleep (CS) protocol consisting of 18 nights with an undisturbed 8-h sleep opportunity. Spontaneous pain was assessed using electronic rating scales during daytime and night-time wake periods. Pain sensitivity was assessed through pressure and heat pain threshold measures every other day of the protocol.

RESULTS

Females responded with higher daytime pain ratings in the ESD compared to the CS condition, while males responded with lower pain ratings (p < 0.05 for condition*sex). Spontaneous pain ratings were higher at night-time than during daytime and worsened across successive nights of sleep disturbances, independent of sex (p < 0.05 for condition*study day*daytime-night-time). Females developed greater pressure pain sensitivity, while males developed greater pain sensitivity to heat in the ESD compared to the CS condition (p < 0.05 for condition*sex).

CONCLUSION

Pain responses to sleep disturbances strongly vary by sex and may contribute to sex differences in the prevalence and symptom burden of many chronic pain conditions. Because the study was not a priori powered on sex, findings are preliminary and require follow-up in larger samples. Findings further suggest to specifically target night-time pain in sleep disturbed individuals, for example, through optimised timing of analgesic-acting medications.

SIGNIFICANCE

Exploration of sex as a modulator suggest that sleep disturbances amplify spontaneous pain and pressure pain sensitivity to a greater extent in females than in males, and this may contribute to females' overrepresentation and disproportionate symptom burden observed for many pain-related disorders for which insomnia is comorbid or a risk factor.

Stretchable hierarchical metal wire networks for neuromorphic emulation of nociception and anti-nociception

Among biomimetic technologies, the incorporation of sensory hardware holds exceptional utility in human-machine interfacing. In this context, devices receptive to nociception and emulating antinociception gain significance as part of pain management. Here we report, a stretchable two-terminal resistive neuromorphic device consisting of a hierarchical Ag microwire network formed using a crack templating protocol. The device demonstrates sensitivity to strain, where the application of strain induces the formation of gaps across active elements, rendering the device electrically open. Following activation by voltage pulses, the device exhibits potentiated states with finite retentions arising from filamentary growth across these gaps due to field migration. Remarkably, the strain-induced functioning alongside controllable gaps enables achieving user-controlled neuromorphic properties, desired for self-adaptive intelligent systems. Interestingly, in the neuromorphic potentiated state, the response to strain is enhanced by ∼106 due to higher sensitivities associated with nanofilaments. The device emulates basic neuromorphic functionalities such as threshold switching, and short-term (STP) and long-term potentiations (LTP). Furthermore, the sensitivity has been exploited in mimicking nociception through strain-induced changes in the potentiated state. Interestingly, repetition of the strain stimulus leads to endurance making the device restore its conductance, thereby emulating adaptation and habituation representing the antinociceptive behavior.

Monolithically integrated neuromorphic electronic skin for biomimetic radiation shielding

Melanogenesis, a natural responsive mechanism of human skin to harmful radiation, is a self-triggered defensive neural activity safeguarding the body from radiation exposure in advance. With the increasing significance of radiation shielding in diverse medical health care and wearable applications, a biomimetic neuromorphic optoelectronic system with adaptive radiation shielding capability is often needed. Here, we demonstrate a transparent and flexible metal oxide-based photovoltaic neuromorphic defensive system. By using a monolithically integrated ultraflexible optoelectronic circuitry and electrochromic device, seamless neural processing for ultraviolet (UV) radiation shielding including history-based sensing, memorizing, risk recognition, and blocking can be realized with piling the entire signal chain into the flexible devices. The UV shielding capability of the system can be evaluated as autonomous blocking up to 97% of UV radiation from 5 to 90 watts per square meter in less than 16.9 seconds, demonstrating autonomously modulated sensitivity and response time corresponding to UV environmental conditions and supplied bias.

A flexible capacitive pressure sensor with a hybrid porous PDMS/SA hydrogel structure for touch/pain detection

Exploring highly sensitive flexible electronic skins (e-skins) that can mimic the tactile and pain perception of human skin is an important prerequisite for achieving biomimetic robots and intelligent prosthetics. However, it is still difficult to realize both touch and pain sensing using a single pressure sensor. Herein, a novel flexible capacitive pressure sensor that can distinguish noxious pressure stimuli is proposed for detecting touch and pain, which is composed of a porous polydimethylsiloxane (PDMS) skeleton and a sodium alginate (SA) hydrogel core. The sensor employs two different working mechanisms depending on the range of external pressure, determining the mechanism of operation for transducing the sense of touch or pain. Such a unique structural design plays a crucial role in enhancing pain perception, leading to maximum sensitivity (14.25 kPa-1) in a large pressure regime (up to 400 kPa) and an adjustable pressure threshold. Moreover, the sensor also exhibits a fast response (45 ms) and recovery speed (70 ms), ensuring a sufficiently fast response to noxious pressure stimuli. Finally, we demonstrate the capabilities of a robotic hand based on the pressure sensor for precisely detecting both touch and pain, which shows great promise in developing intelligent robots and prosthetic limbs to prevent possible damage under external noxious stimuli.

Heterogeneous Integration of Memristive and Piezoresistive MDMO-PPV-Based Copolymers in Nociceptive Transmission with Fast and Slow Pain for an Artificial Pain-Perceptual System

Nociceptive pain perception is a remarkable capability of organisms to be aware of environmental changes and avoid injury, which can be accomplished by specialized pain receptors known as nociceptors with 4 vital properties including threshold, no adaptation, relaxation, and sensitization. Bioinspired systems designed using artificial devices are investigated to imitate the efficacy and functionality of nociceptive transmission. Here, an artificial pain-perceptual system (APPS) with a homogeneous material and heterogeneous integration is proposed to emulate the behavior of fast and slow pain in nociceptive transmission. Retention-differentiated poly[2-methoxy-5-(3,7-dimethyoctyoxyl)-1,4-phenylenevinylene] (MDMO-PPV) memristors with film thicknesses of 160 and 80 nm are manufactured and adopted as A-δ and C nerve fibers of nociceptor conduits, respectively. Additionally, a nociceptor mimic, the ruthenium nanoparticles (Ru-NPs)-doped MDMO-PPV piezoresistive pressure sensor, is fabricated with a noxiously stimulated threshold of 150 kPa. Under the application of pricking and dull noxious stimuli, the current flows predominantly through the memristor to mimic the behavior of fast and slow pain, respectively, in nociceptive transmission with postsynaptic potentiation properties, which is analogous to biological pain perception. The proposed APPS can provide potential advancements in establishing the nervous system, thus enabling the successful development of next-generation neurorobotics, neuroprosthetics, and precision medicine.

The Role of the Thalamus in Nociception: Important but Forgotten

Pain is a complex response to noxious stimuli. Upon detection of the nociceptive stimulus by first-order neurons or nociceptors, an action potential ascends to the spinal dorsal horn, a crucial site for synapsing with second-order neurons. These second-order neurons carry the nociceptive stimulus to supraspinal regions, notably the thalamus. Although extensive research has focused on spinal-level nociceptive mechanisms (e.g., neurotransmitters, receptors, and glial cells), the thalamus is still poorly elucidated. The role of the thalamus in relaying sensory and motor responses to the cortex is well known. However, a comprehensive understanding of the mechanisms in the synapse between the second-order and third-order neurons that transmit this impulse to the somatosensory cortex, where the response is processed and interpreted as pain, is still lacking. Thus, this review investigated the thalamus's role in transmitting nociceptive impulses. Current evidence indicates the involvement of the neurotransmitters glutamate and serotonin, along with NMDA, P2X4, TLR4, FGR, and NLRP3 receptors, as well as signaling pathways including ERK, P38, NF-κB, cytokines, and glial cells at nociceptive synapses within the thalamus.

Moving in pain - A preliminary study evaluating the immediate effects of experimental knee pain on locomotor biomechanics

Pain changes how we move, but it is often confounded by other factors due to disease or injury. Experimental pain offers an opportunity to isolate the independent effect of pain on movement. We used cutaneous electrical stimulation to induce experimental knee pain during locomotion to study the short-term motor adaptions to pain. While other models of experimental pain have been used in locomotion, they lack the ability to modulate pain in real-time. Twelve healthy adults completed the single data collection session where they experienced six pain intensity conditions (0.5, 1, 2, 3, 4, 5 out of 10) and two pain delivery modes (tonic and phasic). Electrodes were placed over the lateral infrapatellar fat pad and medial tibial condyle to deliver the 10 Hz pure sinusoid via a constant current electrical stimulator. Pain intensity was calibrated prior to each walking bout based on the target intensity and was recorded using an 11-point numerical rating scale. Knee joint angles and moments were recorded over the walking bouts and summarized in waveform and discrete outcomes to be compared with baseline walking. Knee joint angles changed during the swing phase of gait, with higher pain intensities resulting in greater knee flexion angles. Minimal changes in joint moments were observed but there was a consistent pattern of decreasing joint stiffness with increasing pain intensity. Habituation was limited across the 30-90 second walking bouts and the electrical current needed to deliver the target pain intensities showed a positive linear relationship. Experimental knee pain shows subtle biomechanical changes and favourable habituation patterns over short walking bouts. Further exploration of this model is needed in real-world walking conditions and over longer timeframes to quantify motor adaptations.

Expression patterns of mechanosensitive ion channel PIEZOs in irreversible pulpitis

BACKGROUND

Mechanosensitive ion channel PIEZOs have been widely reported to involve inflammation and pain. This study aimed to clarify expression patterns of PIEZOs and their potential relations to irreversible pulpitis.

MATERIALS AND METHODS

Normal pulp tissues (n = 29) from patients with impacted third molars and inflamed pulp tissues (n = 23) from patients with irreversible pulpitis were collected. Pain levels were assessed using a numerical rating scale. PIEZO expressions were measured using real-time PCR and then confirmed using GEO datasets GSE77459, immunoblot, and immunohistochemistry staining. Correlations of PIEZO mRNA expression with inflammatory markers, pain markers, or clinical pain levels were evaluated using Spearman's correlation analysis. Univariate analysis was conducted to analyze PIEZO expressions based on pain description and clinical examinations of cold test, percussion, palpation, and bite test.

RESULTS

Compared with normal pulp tissues, mRNA expression levels of PIEZO1 were significantly increased in inflamed pulp tissues, while PIEZO2 was significantly decreased, which was further confirmed in GSE77459 and on a protein and histological level. The positive correlation of the mRNA expression levels between PIEZO1 and inflammatory markers, as well as between PIEZO2 and pain markers, was verified. PIEZO2 expression was also positively correlated with pain levels. Besides, irreversible pulpitis patients who reported continuous pain and who detected a positive response to cold stimulus exhibited a higher expression level of PIEZO2 in the inflamed pulp tissues. By contrast, patients reporting pain duration of more than one week showed a higher expression level of PIEZO1.

CONCLUSIONS

This study demonstrated the upregulation of PIEZO1 and the downregulation of PIEZO2 in irreversible pulpitis and revealed the potential relation of PIEZO1 and PIEZO2 to inflammation and pain. These findings suggested that PIEZOs might play critical roles in the progression of irreversible pulpitis and paved the way for further investigations aimed at novel therapies of irreversible pulpitis by targeting PIEZOs.

An update to pain management after spinal cord injury: from pharmacology to circRNAs

Neuropathic pain (NP) following a spinal cord injury (SCI) is often hard to control and therapies should be focused on the physical, psychological, behavioral, social, and environmental factors that may contribute to chronic sensory symptoms. Novel therapeutic treatments for NP management should be based on the combination of pharmacological and nonpharmacological options. Some of them are addressed in this review with a focus on mechanisms and novel treatments. Several reports demonstrated an aberrant expression of non-coding RNAs (ncRNAs) that may represent key regulatory factors with a crucial role in the pathophysiology of NP and as potential diagnostic biomarkers. This review analyses the latest evidence for cellular and molecular mechanisms associated with the role of circular RNAs (circRNAs) in the management of pain after SCI. Advantages in the use of circRNA are their stability (up to 48 h), and specificity as sponges of different miRNAs related to SCI and nerve injury. The present review discusses novel data about deregulated circRNAs (up or downregulated) that sponge miRNAs, and promote cellular and molecular interactions with mRNAs and proteins. This data support the concept that circRNAs could be considered as novel potential therapeutic targets for NP management especially after spinal cord injuries.