Inhibiting Nav1.7 channels in pulpitis: An in vivo study on neuronal hyperexcitability.

Pulpitis constitutes a significant challenge in clinical management due to its impact on peripheral nerve tissue and the persistence of chronic pain. Despite its clinical importance, the correlation between neuronal activity and the expression of voltage-gated sodium channel 1.7 (Nav1.7) in the trigeminal ganglion (TG) during pulpitis is less investigated. The aim of this study was to examine the relationship between experimentally induced pulpitis and Nav1.7 expression in the TG and to investigate the potential of selective Nav1.7 modulation to attenuate TG abnormal activity associated with pulpitis. Acute pulpitis was induced at the maxillary molar (M1) using allyl isothiocyanate (AITC). The mice were divided into three groups: control, pulpitis model, and pulpitis model treated with ProTx-II, a selective Nav1.7 channel inhibitor. After three days following the surgery, we conducted a recording and comparative analysis of the neural activity of the TG utilizing in vivo optical imaging. Then immunohistochemistry and Western blot were performed to assess changes in the expression levels of extracellular signal-regulated kinase (ERK), c-Fos, collapsin response mediator protein-2 (CRMP2), and Nav1.7 channels. The optical imaging result showed significant neurological excitation in pulpitis TGs. Nav1.7 expressions exhibited upregulation, accompanied by signaling molecular changes suggestive of inflammation and neuroplasticity. In addition, inhibition of Nav1.7 led to reduced neural activity and subsequent decreases in ERK, c-Fos, and CRMP2 levels. These findings suggest the potential for targeting overexpressed Nav1.7 channels to alleviate pain associated with pulpitis, providing practical pain management strategies.

Insular cortex stimulation alleviates neuropathic pain through changes in the expression of collapsin response mediator protein 2 involved in synaptic plasticity.

In recent studies, brain stimulation has shown promising potential to alleviate chronic pain. Although studies have shown that stimulation of pain-related brain regions can induce pain-relieving effects, few studies have elucidated the mechanisms of brain stimulation in the insular cortex (IC). The present study was conducted to explore the changes in characteristic molecules involved in pain modulation mechanisms and to identify the changes in synaptic plasticity after IC stimulation (ICS). Following ICS, pain-relieving behaviors and changes in proteomics were explored. Neuronal activity in the IC after ICS was observed by optical imaging. Western blotting was used to validate the proteomics data and identify the changes in the expression of glutamatergic receptors associated with synaptic plasticity. Experimental results showed that ICS effectively relieved mechanical allodynia, and proteomics identified specific changes in collapsin response mediator protein 2 (CRMP2). Neuronal activity in the neuropathic rats was significantly decreased after ICS. Neuropathic rats showed increased expression levels of phosphorylated CRMP2, alpha amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor (AMPAR), and N-methyl-d-aspartate receptor (NMDAR) subunit 2B (NR2B), which were inhibited by ICS. These results indicate that ICS regulates the synaptic plasticity of ICS through pCRMP2, together with AMPAR and NR2B, to induce pain relief.

Alleviation of peripheral sensitization by quadriceps insertion of cog polydioxanone filaments in knee osteoarthritis rats.

A recently established therapeutic strategy, involving the insertion of biodegradable cog polydioxanone filaments into the quadriceps muscles using the Muscle Enhancement and Support Therapy (MEST) device, has demonstrated significant efficacy in alleviating knee osteoarthritis (OA) pain. This study investigated changes in peripheral sensitization as the potential mechanism underlying MEST-induced pain relief in monoiodoacetate (MIA) induced OA rats. The results revealed that MEST treatment potently reduces MIA-induced sensitization of L3/L4 dorsal root ganglion (DRG) neurons, the primary nociceptor pathway for the knee joint. This reduction in DRG sensitization, as elucidated by voltage-sensitive dye imaging, is accompanied by a diminished overexpression of TRPA1 and NaV1.7, key nociceptor receptors involved in mechanical pain perception. Importantly, these observed alterations strongly correlate with a decrease in mechanically-evoked pain behaviors, providing compelling neurophysiological evidence that MEST treatment alleviates OA pain by suppressing peripheral sensitization.

Diffusion tensor imaging reveals sex differences in pain sensitivity of rats.

Studies on differences in brain structure and function according to sex are reported to contribute to differences in behavior and cognition. However, few studies have investigated brain structures or used tractography to investigate gender differences in pain sensitivity. The identification of tracts involved in sex-based structural differences that show pain sensitivity has remained elusive to date. Here, we attempted to demonstrate the sex differences in pain sensitivity and to clarify its relationship with brain structural connectivity. In this study, pain behavior test and brain diffusion tensor imaging (DTI) were performed in male and female rats and tractography was performed on the whole brain using fiber tracking software. We selected eight brain regions related to pain and performed a tractography analysis of these regions. Fractional anisotropy (FA) measurements using automated tractography revealed sex differences in the anterior cingulate cortex (ACC)-, prefrontal cortex (PFC)-, and ventral posterior thalamus-related brain connections. In addition, the results of the correlation analysis of pain sensitivity and DTI tractography showed differences in mean, axial, and radial diffusivities, as well as FA. This study revealed the potential of DTI for exploring circuits involved in pain sensitivity. The behavioral and functional relevance's of measures derived from DTI tractography is demonstrated by their relationship with pain sensitivity.

Insular cortex stimulation alleviates neuropathic pain via ERK phosphorylation in neurons.

AIMS: The clinical use of brain stimulation is attractive for patients who have side effects or tolerance. However, studies on insular cortex (IC) stimulation are lacking in neuropathic pain. The present study aimed to investigate the effects of IC stimulation (ICS) on neuropathic pain and to determine how ICS modulates pain. METHODS: Changes in pain behaviors were observed following ICS with various parameters in neuropathic rats. Western blotting was performed to assess molecular changes in the expression levels of phosphorylated extracellular signal-regulated kinase (pERK), neurons, astrocytes, and microglia between experimental groups. Immunohistochemistry was performed to investigate the colocalization of pERK with different cell types. RESULTS: The most effective pain-relieving effect was induced at 50 Hz-120 µA in single trial of ICS and it maintained 4 days longer after the termination of repetitive ICS. The expression levels of pERK, astrocytes, and microglia were increased in neuropathic rats. However, after ICS, the expression levels of pERK were decreased, and colocalization of pERK and neurons was reduced in layers 2-3 of the IC. CONCLUSION: These results indicated that ICS attenuated neuropathic pain by the regulation of pERK in neurons located in layers 2-3 of the IC. This preclinical study may enhance the potential use of ICS and identify the therapeutic mechanisms of ICS in neuropathic pain.

Modulation of Neuropathic Pain by Glial Regulation in the Insular Cortex of Rats.

The insular cortex (IC) is known to process pain information. However, analgesic effects of glial inhibition in the IC have not yet been explored. The aim of this study was to investigate pain alleviation effects after neuroglia inhibition in the IC during the early or late phase of pain development. The effects of glial inhibitors in early or late phase inhibition in neuropathic pain were characterized in astrocytes and microglia expressions in the IC of an animal model of neuropathic pain. Changes in withdrawal responses during different stages of inhibition were compared, and morphological changes in glial cells with purinergic receptor expressions were analyzed. Inhibition of glial cells had an analgesic effect that persisted even after drug withdrawal. Both GFAP and CD11b/c expressions were decreased after injection of glial inhibitors. Morphological alterations of astrocytes and microglia were observed with expression changes of purinergic receptors. These findings indicate that inhibition of neuroglia activity in the IC alleviates chronic pain, and that purinergic receptors in glial cells are closely related to chronic pain development.

Inhibition of the Nav1.7 Channel in the Trigeminal Ganglion Relieves Pulpitis Inflammatory Pain.

Pulpitis causes significant changes in the peripheral nervous system, which induce hyperalgesia. However, the relationship between neuronal activity and Nav1.7 expression following pulpal noxious pain has not yet been investigated in the trigeminal ganglion (TG). The aim of our study was to verify whether experimentally induced pulpitis activates the expression of Nav1.7 peripherally and the neuronal activities of the TGs can be affected by Nav1.7 channel inhibition. Acute pulpitis was induced through allyl isothiocyanate (AITC) application to the rat maxillary molar tooth pulp. Three days after AITC application, abnormal pain behaviors were recorded, and the rats were euthanized to allow for immunohistochemical, optical imaging, and western blot analyses of the Nav1.7 expression in the TG. A significant increase in AITC-induced pain-like behaviors and histological evidence of pulpitis were observed. In addition, histological and western blot data showed that Nav1.7 expressions in the TGs were significantly higher in the AITC group than in the naive and saline group rats. Optical imaging showed that the AITC group showed higher neuronal activity after electrical stimulation of the TGs. Additionally, treatment of ProTxII, selective Nav1.7 blocker, on to the TGs in the AITC group effectively suppressed the hyperpolarized activity after electrical stimulation. These findings indicate that the inhibition of the Nav1.7 channel could modulate nociceptive signal processing in the TG following pulp inflammation.

Crosstalk between Neuron and Glial Cells in Oxidative Injury and Neuroprotection.

To counteract oxidative stress and associated brain diseases, antioxidant systems rescue neuronal cells from oxidative stress by neutralizing reactive oxygen species and preserving gene regulation. It is necessary to understand the communication and interactions between brain cells, including neurons, astrocytes and microglia, to understand oxidative stress and antioxidant mechanisms. Here, the role of glia in the protection of neurons against oxidative injury and glia-neuron crosstalk to maintain antioxidant defense mechanisms and brain protection are reviewed. The first part of this review focuses on the role of glia in the morphological and physiological changes required for brain homeostasis under oxidative stress and antioxidant defense mechanisms. The second part focuses on the essential crosstalk between neurons and glia for redox balance in the brain for protection against oxidative stress.

Possible Therapeutic Options for Complex Regional Pain Syndrome.

Complex regional pain syndrome (CRPS) describes an array of painful conditions that are characterized by continuing regional pain. CRPS comprises severe and inappropriate pain in cases of complete recovery after trauma. Research on the pharmacological treatment of CRPS, however, has not been well investigated. In this study, we compared the pain relief effects of different drugs (URB597, pyrrolidine dithiocarbamate, and hydralazine) in a rat model of chronic post-ischemic pain-induced CRPS. After drug injection, CRPS-induced mechanical allodynia was significantly recovered. After three repetitive drug injections, mechanical sensitivity generally improved as hyper-nociception subsided. Reduced Nav1.7 expression at dorsal root ganglions (DRGs) was observed in the drug treatment groups. Neural imaging analysis revealed decreased neural activity for each drug treatment, compared to vehicle. In addition, treatments significantly reduced IL-1ß, IL-6, and TNFα expression in DRGs. These results indicated that drugs could reduce the expression of inflammatory factors and alleviate the symptoms of chronic post-ischemic pain-induced CRPS.

Combined treatment of Taraxaci Herba and R7050 alleviates the symptoms of herpes simplex virus-induced Behçet's disease in rats.

BACKGROUND: Behçet's disease (BD) is a chronic inflammatory systemic disease that affects multiple organs. The causes of BD are still unknown, but it is primarily characterized by autoimmune reaction in the blood vessels. Current research focuses on treatments that can reduce the non-typical inflammatory responses of BD. Nevertheless, studies on improving the inflammatory effect of BD using inflammation mechanisms are still insufficient. Therefore, we conducted the integrated treatments related to inflammation modulation and achieved alleviation of symptoms in BD mice. METHODS: To understand the complex etiology of BD and compare its management, the herpes simplex virus (HSV)-induced BD mouse model was used. In order to alleviate the inflammatory response in BD mice, Taraxaci Herba (TH, herbal medicine), R7050-a TNFα inhibitor, and a mixture of TH and R7050 were injected for 2 weeks repetitively. The SCORAD index was examined to evaluate the cutaneous inflammations. In addition, histological changes and inflammatory factors were analyzed. RESULTS: Repetitive injection of TH and/or R7050 reduced the symptoms of BD and significantly decreased IL-6, IL-1ß, and TNFα in blood sera. Moreover, this treatment reduced the ulcers and the deterioration of skin. CONCLUSIONS: The results of our study showed that the down-regulation of inflammatory factors is related to the control of immune responses in BD models, suggesting that a mixed drug treatment may be more effective in improving the condition of BD.

Chronic Treatment of Ascorbic Acid Leads to Age-Dependent Neuroprotection against Oxidative Injury in Hippocampal Slice Cultures.

Increased oxidative damage in the brain, which increases with age, is the cause of abnormal brain function and various diseases. Ascorbic acid (AA) is known as an endogenous antioxidant that provides neuronal protection against oxidative damage. However, with aging, its extracellular concentrations and uptake decrease in the brain. Few studies have dealt with age-related functional changes in the brain to sustained ascorbate supplementation. This study aimed to investigate the susceptibility of hippocampal neurons to oxidative injury following acute and chronic AA administration. Oxidative stress was induced by kainic acid (KA, 5 µM) for 18 h in hippocampal slice cultures. After KA exposure, less neuronal cell death was observed in the 3 w cultured slice compared to the 9 w cultured slice. In the chronic AA treatment (6 w), the 9 w-daily group showed reduced neuronal cell death and increased superoxide dismutase (SOD) and Nrf2 expressions compared to the 9 w. In addition, the 9 w group showed delayed latencies and reduced signal activity compared to the 3 w, while the 9 w-daily group showed shorter latencies and increased signal activity than the 9 w. These results suggest that the maintenance of the antioxidant system by chronic AA treatment during aging could preserve redox capacity to protect hippocampal neurons from age-related oxidative stress.

Manganese-enhanced MRI depicts a reduction in brain responses to nociception upon mTOR inhibition in chronic pain rats.

Neuropathic pain induced by a nerve injury can lead to chronic pain. Recent studies have reported hyperactive neural activities in the nociceptive-related area of the brain as a result of chronic pain. Although cerebral activities associated with hyperalgesia and allodynia in chronic pain models are difficult to represent with functional imaging techniques, advances in manganese (Mn)-enhanced magnetic resonance imaging (MEMRI) could facilitate the visualization of the activation of pain-specific neural responses in the cerebral cortex. In order to investigate the alleviation of pain nociception by mammalian target of rapamycin (mTOR) modulation, we observed cerebrocortical excitability changes and compared regional Mn2+ enhancement after mTOR inhibition. At day 7 after nerve injury, drugs were applied into the intracortical area, and drug (Vehicle, Torin1, and XL388) effects were compared within groups using MEMRI. Therein, signal intensities of the insular cortex (IC), primary somatosensory cortex of the hind limb region, motor cortex 1/2, and anterior cingulate cortex regions were significantly reduced after application of mTOR inhibitors (Torin1 and XL388). Furthermore, rostral-caudal analysis of the IC indicated that the rostral region of the IC was more strongly associated with pain perception than the caudal region. Our data suggest that MEMRI can depict pain-related signal changes in the brain and that mTOR inhibition is closely correlated with pain modulation in chronic pain rats.

Neuroprotective Effect of Antioxidants in the Brain.

The brain is vulnerable to excessive oxidative insults because of its abundant lipid content, high energy requirements, and weak antioxidant capacity. Reactive oxygen species (ROS) increase susceptibility to neuronal damage and functional deficits, via oxidative changes in the brain in neurodegenerative diseases. Overabundance and abnormal levels of ROS and/or overload of metals are regulated by cellular defense mechanisms, intracellular signaling, and physiological functions of antioxidants in the brain. Single and/or complex antioxidant compounds targeting oxidative stress, redox metals, and neuronal cell death have been evaluated in multiple preclinical and clinical trials as a complementary therapeutic strategy for combating oxidative stress associated with neurodegenerative diseases. Herein, we present a general analysis and overview of various antioxidants and suggest potential courses of antioxidant treatments for the neuroprotection of the brain from oxidative injury. This review focuses on enzymatic and non-enzymatic antioxidant mechanisms in the brain and examines the relative advantages and methodological concerns when assessing antioxidant compounds for the treatment of neurodegenerative disorders.

Effects of mTOR inhibitors on neuropathic pain revealed by optical imaging of the insular cortex in rats.

In the pain matrix, the insular cortex (IC) is mainly involved in discriminative sensory and motivative emotion. Abnormal signal transmission from injury site causes neuropathic pain, which generates enhanced synaptic plasticity. The mammalian target of rapamycin (mTOR) complex is the key regulator of protein synthesis; it is involved in the modulation of synaptic plasticity. To date, there has been no report on the changes in optical signals in the IC under neuropathic condition after treatment with mTOR inhibitors, such as Torin1 and XL388. Therefore, we aimed to determine the pain-relieving effect of mTOR inhibitors (Torin1 and XL388) and observe the changes in optical signals in the IC after treatment. Mechanical threshold was measured in adult male Sprague-Dawley rats after neuropathic surgery, and therapeutic effect of inhibitors was assessed on post-operative day 7 following the microinjection of Torin1 or XL388 into the IC. Optical signals were acquired to observe the neuronal activity of the IC in response to peripheral stimulation before and after treatment with mTOR inhibitors. Consequently, the inhibitors showed the most effective alleviation 4 h after microinjection into the IC. In optical imaging, peak amplitudes of optical signals and areas of activated regions were reduced after treatment with Torin1 and XL388. However, there were no significant optical signal changes in the IC before and after vehicle application. These findings suggested that Torin1 and XL388 are associated with the alleviation of neuronal activity that is excessively manifested in the IC, and is assumed to diminish synaptic plasticity.

Astroglial changes in the zona incerta in response to motor cortex stimulation in a rat model of chronic neuropathy.

Although astrocytes are known to regulate synaptic transmission and affect new memory formation by influencing long-term potentiation and functional synaptic plasticity, their role in pain modulation is poorly understood. Motor cortex stimulation (MCS) has been used to reduce neuropathic pain through the incertothalamic pathway, including the primary motor cortex (M1) and the zona incerta (ZI). However, there has been no in-depth study of these modulatory effects and region-specific changes in neural plasticity. In this study, we investigated the effects of MCS-induced pain modulation as well as the relationship between the ZI neuroplasticity and MCS-induced pain alleviation in neuropathic pain (NP). MCS-induced threshold changes were evaluated after daily MCS. Then, the morphological changes of glial cells were compared by tissue staining. In order to quantify the neuroplasticity, MAP2, PSD95, and synapsin in the ZI and M1 were measured and analyzed with western blot. In behavioral test, repetitive MCS reduced NP in nerve-injured rats. We also observed recovered GFAP expression in the NP with MCS rats. In the NP with sham MCS rats, increased CD68 level was observed. In the NP with MCS group, increased mGluR1 expression was observed. Analysis of synaptogenesis-related molecules in the M1 and ZI revealed that synaptic changes occured in the M1, and increased astrocytes in the ZI were more closely associated with pain alleviation after MCS. Our findings suggest that MCS may modulate the astrocyte activities in the ZI and synaptic changes in the M1. Our results may provide new insight into the important and numerous roles of astrocytes in the formation and function.

mTOR signaling intervention by Torin1 and XL388 in the insular cortex alleviates neuropathic pain.

Signaling by mammalian target of rapamycin (mTOR), a kinase regulator of protein synthesis, has been implicated in the development of chronic pain. The mTOR comprises two distinct protein complexes, mTOR complex 1 (mTORC1) and mTORC2. Although effective inhibitors of mTORC1 and C2 have been developed, studies on the effect of these inhibitors related to pain modulation are still lacking. This study was conducted to determine the inhibitory effects of Torin1 and XL388 in an animal model of neuropathic pain. Seven days after neuropathic surgery, Torin1 or XL388 were microinjected into the insular cortex (IC) of nerve-injured animals and behavioral changes were assessed. Administration of Torin1 or XL388 into the IC significantly increased mechanical thresholds and reduced mechanical allodynia. At the immunoblotting results, Torin1 and XL388 significantly reduced phosphorylation of mTOR, 4E-BP1, p70S6K, and PKCα, without affecting Akt. These results strongly suggest that Torin1 and XL388 may attenuate neuropathic pain via inhibition of mTORC1 and mTORC2 in the IC.

Manganese-enhanced magnetic resonance imaging of the spinal cord in rats with formalin-induced pain.

Manganese-enhanced magnetic resonance imaging (MEMRI) is based on neuronal activity-dependent manganese uptake, and provides information about nervous system function. However, systematic studies of pain processing using MEMRI are rare, and few investigations of pain using MEMRI have been performed in the spinal cord. Herein, we investigated the pain dependence of manganese ions administered in the rat spinal cord. MnCl2 was administered into the spinal cord via an intrathecal catheter before formalin injection into the right hind paw (50 µL of 5% formalin). The duration of flinching behavior was recorded and analyzed to measure formalin-induced pain. After the behavioral test, rats were sacrificed with an overdose of urethane (50 mg/kg), and spine samples were extracted and post-fixed in 4% paraformaldehyde solution. The samples were stored in 30% sucrose until molecular resonance (MR) scanning was performed. In axial Mn2+ enhancement images of the spinal cord, Mn2+ levels were found to be significantly elevated on the ipsilateral side of the spinal cord in formalin-injected rats. To confirm pain-dependent Mn enhancement in the spinal cord, c-Fos expression was analyzed, and was found to be increased in the formalin-injected rats. These results indicate that MEMRI is useful for functional analysis of the spinal cord under pain conditions. The gray matter appears to be the focus of intense paramagnetic signals. MEMRI may provide an effective technique for visualizing activity-dependent patterns in the spinal cord.

Repetitive motor cortex stimulation reinforces the pain modulation circuits of peripheral neuropathic pain.

Recent evidence indicates that motor cortex stimulation (MCS) is a potentially effective treatment for chronic neuropathic pain. However, the neural mechanisms underlying the attenuated hyperalgesia after MCS are not completely understood. In this study, we investigated the neural mechanism of the effects of MCS using an animal model of neuropathic pain. After 10 daily sessions of MCS, repetitive MCS reduced mechanical allodynia and contributed to neuronal changes in the anterior cingulate cortex (ACC). Interestingly, inhibition of protein kinase M zeta (PKMζ), a regulator of synaptic plasticity, in the ACC blocked the effects of repetitive MCS. Histological and molecular studies showed a significantly increased level of glial fibrillary acidic protein (GFAP) expression in the ACC after peripheral neuropathy, and neither MCS treatment nor ZIP administration affected this increase. These results suggest that repetitive MCS can attenuate the mechanical allodynia in neuropathic pain, and that the activation of PKMζ in the ACC may play a role in the modulation of neuropathic pain via MCS.

Inhibition of Mammalian Target of Rapamycin (mTOR) Signaling in the Insular Cortex Alleviates Neuropathic Pain after Peripheral Nerve Injury.

Injury of peripheral nerves can trigger neuropathic pain, producing allodynia and hyperalgesia via peripheral and central sensitization. Recent studies have focused on the role of the insular cortex (IC) in neuropathic pain. Because the IC is thought to store pain-related memories, translational regulation in this structure may reveal novel targets for controlling chronic pain. Signaling via mammalian target of rapamycin (mTOR), which is known to control mRNA translation and influence synaptic plasticity, has been studied at the spinal level in neuropathic pain, but its role in the IC under these conditions remains elusive. Therefore, this study was conducted to determine the role of mTOR signaling in neuropathic pain and to assess the potential therapeutic effects of rapamycin, an inhibitor of mTORC1, in the IC of rats with neuropathic pain. Mechanical allodynia was assessed in adult male Sprague-Dawley rats after neuropathic surgery and following microinjections of rapamycin into the IC on postoperative days (PODs) 3 and 7. Optical recording was conducted to observe the neural responses of the IC to peripheral stimulation. Rapamycin reduced mechanical allodynia and downregulated the expression of postsynaptic density protein 95 (PSD95), decreased neural excitability in the IC, thereby inhibiting neuropathic pain-induced synaptic plasticity. These findings suggest that mTOR signaling in the IC may be a critical molecular mechanism modulating neuropathic pain.

Spatiotemporal changes of optical signals in the somatosensory cortex of neuropathic rats after electroacupuncture stimulation.

BACKGROUND: Peripheral nerve injury causes physiological changes in primary afferent neurons. Neuropathic pain associated with peripheral nerve injuries may reflect changes in the excitability of the nervous system, including the spinothalamic tract. Current alternative medical research indicates that acupuncture stimulation has analgesic effects in various pain symptoms. However, activation changes in the somatosensory cortex of the brain by acupuncture stimulation remain poorly understood. The present study was conducted to monitor the changes in cortical excitability, using optical imaging with voltage-sensitive dye (VSD) in neuropathic rats after electroacupuncture (EA) stimulation. METHODS: Male Sprague-Dawley rats were divided into three groups: control (intact), sham injury, and neuropathic pain rats. Under pentobarbital anesthesia, rats were subjected to nerve injury with tight ligation and incision of the tibial and sural nerves in the left hind paw. For optical imaging, the rats were re-anesthetized with urethane, and followed by craniotomy. The exposed primary somatosensory cortex (S1) was stained with VSD for one hour. Optical signals were recorded from the S1 cortex, before and after EA stimulation on Zusanli (ST36) and Yinlingquan (SP9). RESULTS: After peripheral stimulation, control and sham injury rats did not show significant signal changes in the S1 cortex. However, inflamed and amplified neural activities were observed in the S1 cortex of nerve-injured rats. Furthermore, the optical signals and region of activation in the S1 cortex were reduced substantially after EA stimulation, and recovered in a time-dependent manner. The peak fluorescence intensity was significantly reduced until 90 min after EA stimulation (Pre-EA: 0.25 ± 0.04 and Post-EA 0 min: 0.01 ± 0.01), and maximum activated area was also significantly attenuated until 60 min after EA stimulation (Pre-EA: 37.2 ± 1.79 and Post-EA 0 min: 0.01 ± 0.10). CONCLUSION: Our results indicate that EA stimulation has inhibitory effects on excitatory neuronal signaling in the S1 cortex, caused by noxious stimulation in neuropathic pain. These findings suggest that EA stimulation warrants further study as a potential adjuvant modulation of neuropathic pain.