Complex regional pain syndrome type-I (CRPS-I) represents a type of neurovascular condition featured by severe pain in affected extremities. Few treatments have proven effective for CRPS-I. ...Electroacupuncture (EA) is an effective therapy for pain relief. We explored the mechanism through which EA ameliorates pain in a rat CRPS-I model. The chronic postischemic pain (CPIP) model was established using Sprague-Dawley rats to mimic CRPS-I. We found that oxidative stress-related biological process was among the predominant biological processes in affected hindpaw of CPIP rats. Oxidative stress occurred primarily in local hindpaw but not in the spinal cord or serum of model rats. Antioxidant N-acetyl cysteine (NAC) attenuated mechanical allodynia and spinal glia overactivation in CPIP model rats, whereas locally increasing oxidative stress is sufficient to induce chronic pain and spinal glia overactivation in naive rats. EA exerted remarkable antiallodynia on CPIP rats by reducing local oxidative stress via enhancing nuclear factor erythroid 2-related factor 2 (Nrf2) expression. Pharmacological blocking Nrf2 abolished antioxidative and antiallodynic effects of EA. EA reduced spinal glia overactivation, attenuated the upregulation of inflammatory cytokines, reduced the enhanced TRPA1 channel activity in dorsal root ganglion neurons innervating the hindpaws, and improved blood flow dysfunction in hindpaws of CPIP rats, all of which were mimicked by NAC treatment. Thus, we identified local oxidative injury as an important contributor to pathogenesis of animal CRPS-I model. EA targets local oxidative injury by enhancing endogenous Nrf2-mediated antioxidative mechanism to relieve pain and inflammation. Our study indicates EA can be an alternative option for CRPS-I management.
ObjectiveBesides neurons, activated microglia and astrocytes in the spinal cord dorsal horn (SCDH) contribute to the pathogenesis of chronic pain. Electroacupuncture (EA) has been used widely to ...treat various chronic pain diseases, however, the underlying mechanisms of EA are still not fully understood.MethodsMale Sprague-Dawley rats were randomly divided into four groups, including an untreated healthy Control group (n=14), a True-spinal nerve ligation (SNL) group that underwent SNL and remained untreated (n=25), a True-SNL+EA group that underwent SNL followed by EA treatment (n=25), and a Sham-SNL group that underwent sham surgery and remained untreated (n=15). SNL was performed unilaterally at L5 and EA was applied to ST36 and BL60 bilaterally once per day. Paw withdrawal thresholds (PWTs) were measured ipsilaterally at baseline and 1, 3, 7, and 14 days after ligation. Activation of microglia and astrocytes in the SCDH were examined bilaterally by immunofluorescence staining, and concentrations of interleukin-1β (IL-1β) and interleukin (IL-6) were measured in the ipsilateral SCDH by ELISA.ResultsSNL significantly decreased PWTs and activated glial cells in the superficial laminae of the ipsilateral SCDH. In rats with SNL, glial fibrillary acidic protein (GFAP) immunoreactivity peaked at 7 days and was maintained until 14 days post-ligation, while anti-integrin alphaM (OX-42) immunoreactivity peaked at 3 days and declined gradually. EA significantly alleviated SNL-induced mechanical allodynia. Furthermore, EA reduced microglial activation (OX-42 positive ratios) in the lumbar SCDH at 3 days post-ligation and suppressed astrocyte activation (GFAP positive ratios) at all time points observed.ConclusionsEA stimulation alleviates SNL-induced neuropathic pain, at least in part through inhibition of spinal glial activation. Moreover, inhibition of spinal microglia and astrocyte activation may contribute to the immediate effects and maintenance of EA analgesia, respectively.
Objective. Electroacupuncture (EA) is reported effective in alleviating pain- related emotion; however, the underlying mechanism of its effects still needs to be elucidated. The NPS-NPSR system has ...been validated for the involvement in the modulation of analgesia and emotional behavior. Here, we aimed to investigate the role of the NPS-NPSR system in the anterior cingulate cortex (ACC), hypothalamus, and central amygdala (CeA) in the use of EA to relieve affective pain modeled by complete Freund's adjuvant- (CFA-) evoked conditioned place aversion (C-CPA). Materials and Methods. CFA injection combined with a CPA paradigm was introduced to establish the C-CPA model, and the elevated O-maze (EOM) was used to test the behavioral changes after model establishment. We further explored the expression of NPS and NPSR at the protein and gene levels in the brain regions of interest by immunofluorescence staining and quantitative real-time PCR. Results. We observed that EA stimulation delivered to the bilateral Zusanli (ST36) and Kunlun (BL60) acupoints remarkably inhibited sensory pain, pain-evoked place aversion, and anxiety-like behavior. The current study showed that EA significantly enhanced the protein expression of this peptide system in the ACC and hypothalamus, while the elevated expression of NPSR protein alone was just confined to the affected side in the CeA. Moreover, EA remarkably upregulated the mRNA expression of NPS in CeA, ACC, and hypothalamus and NPSR mRNA in the hypothalamus and CeA. Conclusions. These data suggest the effectiveness of EA in alleviating affective pain, and these benefits may at least partially be attributable to the upregulation of the NPS-NPSR system in the ACC and hypothalamus.
Objective. Electroacupuncture (EA) is reported effective in alleviating pain-related emotion; however, the underlying mechanism of its effects still needs to be elucidated. The NPS-NPSR system has ...been validated for the involvement in the modulation of analgesia and emotional behavior. Here, we aimed to investigate the role of the NPS-NPSR system in the anterior cingulate cortex (ACC), hypothalamus, and central amygdala (CeA) in the use of EA to relieve affective pain modeled by complete Freund’s adjuvant- (CFA-) evoked conditioned place aversion (C-CPA). Materials and Methods. CFA injection combined with a CPA paradigm was introduced to establish the C-CPA model, and the elevated O-maze (EOM) was used to test the behavioral changes after model establishment. We further explored the expression of NPS and NPSR at the protein and gene levels in the brain regions of interest by immunofluorescence staining and quantitative real-time PCR. Results. We observed that EA stimulation delivered to the bilateral Zusanli (ST36) and Kunlun (BL60) acupoints remarkably inhibited sensory pain, pain-evoked place aversion, and anxiety-like behavior. The current study showed that EA significantly enhanced the protein expression of this peptide system in the ACC and hypothalamus, while the elevated expression of NPSR protein alone was just confined to the affected side in the CeA. Moreover, EA remarkably upregulated the mRNA expression of NPS in CeA, ACC, and hypothalamus and NPSR mRNA in the hypothalamus and CeA. Conclusions. These data suggest the effectiveness of EA in alleviating affective pain, and these benefits may at least partially be attributable to the upregulation of the NPS-NPSR system in the ACC and hypothalamus.
Pain is considered as a multidimensional conscious experience that includes a sensory component and a negative affective-motivational component. Electroacupuncture (EA) is widely used to treat pain ...and pain-induced negative emotions, however, little is known about the mechanisms underlying the effect of EA.
This study investigated the effect of EA on alleviating the anxiety-like behaviors in pain aversion rats and its anterior cingulate cortex (ACC) regulation mechanism.
After a Freund's complete adjuvant (CFA)-conditioned place aversion (C-CPA) model was established in rats, EA treatment (2/100 Hz, 30 min, once/day, 4 days totally) was applied at bilateral Zusanli (ST36) and Kunlun (BL60) acupoints. Von Frey filaments were used to measure changes of pain withdrawal threshold (PWT) at indicated time points. Elevated zero maze (EZM) was used to investigate the changes of pain-related anxiety and CPA was used to investigate the changes of pain aversion. The protein expression levels of GAD67, PV, and NPY in ACC were detected by Western blotting.
Compared with the control group, the staying time in the "CFA-paired compartment" was significantly reduced, and the PWT was decreased in model group. In the EZM assessment, the distance and the time in open arm, as well as the number of open arm entries of model group were significantly lower than those in the control group. In the CPA assessment, the time spent in the "CFA-paired compartment" was significantly decreased in model group compared with control group, and EA reversed the changes in pain sensation and in pain-related emotions. Western blotting showed that the NPY level, but not the levels of GAD67 and PV, was significantly increased in the ACC of the model group compared to that of the control group. The increased expression of NPY in the ACC was significantly downregulated by EA, while sham EA produced no such effect.
EA can effectively relieve the pain and pain-related emotions, and its mechanism may be achieved by down-regulating the expression of NPY in the ACC.
EA stimulation effectively reverses chronic inflammatory pain and its negative emotions by downregulating the expression of NPY protein in the ACC
Display omitted
Objective: Electroacupuncture (EA) is an alternative treatment option for pain. Different frequencies of EA have different pain-relieving effects; however, the central mechanism is still not well ...understood. Methods: The FosTRAP:Ai9 mice were divided into three groups (sham, 2 Hz, and 100 Hz). The mice were intraperitoneally injected with 4-hydroxytamoxifen (4-OHT) immediately after EA at Zusanli (ST36) for 30 min to record the activated neurons. One week later, the mice were sacrificed, and the number of TRAP-treated neurons activated by EA in the thalamus, amygdala, cortex, and hypothalamus was determined. Results: In the cortex, 2 Hz EA activated more TRAP-treated neurons than 100 Hz EA did in the cingulate cortex area 1 (Cg1) and primary somatosensory cortex (S1), and 2 Hz and 100 Hz EAs did not differ from sham EA. TRAP-treated neurons activated by 2 Hz EA were upregulated in the insular cortex (IC) and secondary somatosensory cortex (S2) compared with those activated by 100 Hz and sham EA. In the thalamus, the number of TRAP-treated neurons activated by 2 Hz EA was elevated in the paraventricular thalamic nucleus (PV) compared with those activated by sham EA. In the ventrolateral thalamic nucleus (VL), the number of TRAP-treated neurons activated by 2 Hz EA was significantly upregulated compared with those activated by 100 Hz EA, and sham EA showed no difference compared to 2 Hz EA or 100 Hz EA. TRAP-treated neurons were more frequently activated in the ventral posterolateral thalamic nucleus (VPL) by 2 Hz EA than by 100 Hz or sham EA. Conclusion: Low-frequency EA ST36 effectively activates neurons in the Cg1, S1, S2, IC, VPL, PV, and VL. The enhanced excitability of the aforementioned nuclei induced by low-frequency EA may be related to its superior efficacy in the treatment of neuropathological pain.
Background: Acute pain can transition to chronic pain, presenting a major clinical challenge. Electroacupuncture (EA) can partly prevent the transition from acute to chronic pain. However, little is ...known about the mechanisms underlying the effect of EA. This study investigated the effect of EA on pain transition and the activation of metabotropic glutamate receptor 5 (mGluR5)-protein kinase C epsilon (PKCepsilon) signaling pathway in the dorsal root ganglia (DRG). Methods: The hyperalgesic priming model was established by the sequential intraplantar injection of carrageenan (1%, 100 microL) and prostaglandin E2 (PGE2) into the left hind paw of rats. EA treatment (2/100 Hz, 30 min, once/day) was applied at bilateral Zusanli (ST36) and Kunlun (BL60) acupoints in rats. Von Frey filaments were used to investigate the mechanical withdrawal threshold (MWT) at different time points. The protein expression levels of mGluR5 and PKCepsilon in the ipsilateral L4-L6 DRGs of rats were detected by Western blot. Some pharmacological experiments were performed to evaluate the relationship between mGluR5, PKCepsilon and the MWT. It was also used to test the effects of EA on the expression levels of mGluR5 and PKCepsilon and changes in the MWT. Results: Sequential injection of carrageenan and PGE2 significantly decreased the MWT of rats and up-regulated the expression level of mGluR5 and PKCepsilon in the ipsilateral L4-L6 DRGs. EA can reverse the hyperalgesic priming induced by sequential injection of carrageenan/PGE and down-regulate the protein expression of mGluR5 and PKCepsilon. Glutamate injection instead of PGE2 can mimic the hyperalgesic priming model. Pharmacological blocking of mGluR5 with specific antagonist MTEP can prevent the hyperalgesic priming and inhibit the activation of PKCepsilon in DRGs. Furthermore, EA also produced analgesic effect on the hyperalgesic priming rats induced by carrageenan/mGluR5 injection and inhibited the high expression of PKCepsilon. Sham EA produced none analgesic and regulatory effect. Conclusion: EA can regulate pain transition and it may relate with its inhibitory effect on the activation of mGluR5-PKCepsilon signaling pathway in the DRGs. Keywords: electroacupuncture, pain transition, hyperalgesic priming, mGluR5, PKCepsilon, DRGs
Acute pain can transition to chronic pain, presenting a major clinical challenge. Electroacupuncture (EA) can partly prevent the transition from acute to chronic pain. However, little is known about ...the mechanisms underlying the effect of EA. This study investigated the effect of EA on pain transition and the activation of metabotropic glutamate receptor 5 (mGluR5)-protein kinase C epsilon (PKCε) signaling pathway in the dorsal root ganglia (DRG).
The hyperalgesic priming model was established by the sequential intraplantar injection of carrageenan (1%, 100 μL) and prostaglandin E2 (PGE2) into the left hind paw of rats. EA treatment (2/100 Hz, 30 min, once/day) was applied at bilateral Zusanli (ST36) and Kunlun (BL60) acupoints in rats. Von Frey filaments were used to investigate the mechanical withdrawal threshold (MWT) at different time points. The protein expression levels of mGluR5 and PKCε in the ipsilateral L4-L6 DRGs of rats were detected by Western blot. Some pharmacological experiments were performed to evaluate the relationship between mGluR5, PKCε and the MWT. It was also used to test the effects of EA on the expression levels of mGluR5 and PKCε and changes in the MWT.
Sequential injection of carrageenan and PGE2 significantly decreased the MWT of rats and up-regulated the expression level of mGluR5 and PKCε in the ipsilateral L4-L6 DRGs. EA can reverse the hyperalgesic priming induced by sequential injection of carrageenan/PGE and down-regulate the protein expression of mGluR5 and PKCε. Glutamate injection instead of PGE2 can mimic the hyperalgesic priming model. Pharmacological blocking of mGluR5 with specific antagonist MTEP can prevent the hyperalgesic priming and inhibit the activation of PKCε in DRGs. Furthermore, EA also produced analgesic effect on the hyperalgesic priming rats induced by carrageenan/mGluR5 injection and inhibited the high expression of PKCε. Sham EA produced none analgesic and regulatory effect.
EA can regulate pain transition and it may relate with its inhibitory effect on the activation of mGluR5-PKCε signaling pathway in the DRGs.
Pain memory is commonly considered an underlying cause of chronic pain and is also responsible for a range of anxiety. Electroacupuncture (EA) has been shown to ameliorate pain memories and exert ...anti-anxiety effects. Previous research has indicated that GABAergic neurons and/or GABA receptors (GABARs) in the midcingulate cortex (MCC) have potential associations with chronic pain and anxiety. However, there is no known empirical research that has specifically studied the effects of EA on the GABAergic system in the MCC. Here, we used cross-injection of carrageenan to establish the pain memory rats model. Immunofluorescence were used to detect the excitability of GABAergic neurons within MCC. Von Frey filament, elevated zero maze, and open field tests were used to measure mechanical allodynia and anxiety-like behaviors, combined with chemogenetic and pharmacologic technologies. Finally, this study provides evidence that pain memories contribute to generalized negative emotions and that downregulating the activity of GABAergic neurons within MCC could block pain memories and reverse anxiety emotion. Specifically, GABA
R is involved in pain memory and related anxiety-like behaviors. Activation of GABAergic neurons in the MCC did not reverse the effects of EA on pain memories and related anxiety-like behaviors, whereas these effects could be reversed by a GABA
R agonist. These findings highlight the functional significance of GABA
R in the EA-mediated attenuation of pain memories and related anxiety-like behaviors in rats.
Comorbid chronic neuropathic pain and anxiety is a common disease that represents a major clinical challenge. The underlying mechanisms of chronic neuropathic pain and anxiety are not entirely ...understood, which limits the exploration of effective treatment methods. Glutamatergic neurons in the ventrolateral periaqueductal gray (vlPAG) have been implicated in regulating pain, but the potential roles of the vlPAG in neuropathic pain-induced anxiety have not been investigated. Herein, whole-cell recording and immunofluorescence showed that the excitability of CamkIIα neurons in the vlPAG (vlPAG CamkIIα+ neurons) was decreased in mice with spared nerve injury (SNI), while electroacupuncture (EA) activated these neurons. We also showed that chemogenetic inhibition of vlPAG CamkIIα+ neurons resulted in allodynia and anxiety-like behaviors in naive mice. Furthermore, chemogenetic activation of vlPAG CamkIIα+ neurons reduced anxiety-like behaviors and allodynia in mice with SNI, and EA had a similar effect in alleviating these symptoms. Nevertheless, EA combined with chemogenetic activation failed to further relieve allodynia and anxiety-like behaviors. Artificial inhibition of vlPAG CamkIIα+ neurons abolished the analgesic and anxiolytic effects of EA. Overall, our study reveals a novel mechanism of neuropathic pain-induced anxiety and shows that EA may relieve comorbid chronic neuropathic pain and anxiety by activating vlPAG CamkIIα+ neurons. Significance Statement Neuropathic pain is clinically accompanied by anxiety. Both glutamatergic neurons in the ventrolateral periaqueductal gray (vlPAG) and electroacupuncture (EA) have demonstrated analgesic properties. However, the efficacy of these interventions in addressing neuropathic pain and its concomitant anxiety has yet to be fully elucidated. In a mice model of spared nerve injury (SNI), we observed a decreased excitability of vlPAG CamkIIα neurons. Remarkably, EA treatment significantly enhanced the excitability of these neurons. Further, chemogenetic activation of vlPAG CamkIIα+ neurons not only resulted in analgesia but also mitigated anxiety-like behaviors in SNI mice, mirroring the effects observed with EA treatment. Conversely, inhibition of vlPAG CamkIIα+ neurons activity in naive mice reduced pain thresholds and induced anxiety-like behavior, while also negating the beneficial effects of EA. These findings provide novel insights into the mechanistic interplay between chronic neuropathic pain and anxiety, highlighting the therapeutic potential of targeting vlPAG glutamatergic neurons in these conditions.
PDF
