Excitatory amino acid receptor antagonists and electroacupuncture synergetically inhibit carrageenan-induced behavioral hyperalgesia and spinal fos expression in rats

Electroacupuncture Alleviates Streptozotocin-Induced Diabetic Neuropathic Pain via the TRPV1-Mediated CaMKII/CREB Pathway in Rats

Diabetic neuropathic pain (DNP) is a diabetic complication that causes severe pain and deeply impacts the quality of the sufferer's daily life. Currently, contemporary clinical treatments for DNP generally exhibit a deficiency in effectiveness. Electroacupuncture (EA) is recognized as a highly effective and safe treatment for DNP with few side effects. Regrettably, the processes via which EA alleviates DNP are still poorly characterized. Transient receptor potential vanilloid 1 (TRPV1) and phosphorylated calcium/calmodulin-dependent protein kinase II (p-CaMKII) are overexpressed on spinal cord dorsal horn (SCDH) in DNP rats, and co-localization is observed between them. Capsazepine, a TRPV1 antagonist, effectively reduced nociceptive hypersensitivity and downregulated the overexpression of phosphorylated CaMKIIα in rats with DNP. Conversely, the CaMKII inhibitor KN-93 did not have any impact on TRPV1. EA alleviated heightened sensitivity to pain caused by nociceptive stimuli and downregulated the level of TRPV1, p-CaMKIIα, and phosphorylated cyclic adenosine monophosphate response element-binding protein (p-CREB) in DNP rats. Intrathecal injection of capsaicin, on the other hand, reversed the above effects of EA. These findings indicated that the CaMKII/CREB pathway on SCDH is located downstream of TRPV1 and is affected by TRPV1. EA alleviates DNP through the TRPV1-mediated CaMKII/CREB pathway.

Acupuncture therapies for relieving pain in pelvic inflammatory disease: A systematic review and meta-analysis

BACKGROUND

Studies investigating the effectiveness of acupuncture therapies in alleviating pain in pelvic inflammatory disease (PID) have gained increasing attention. However, to date, there have been no systematic reviews and meta-analyses providing high-quality evidence regarding the efficacy and safety of acupuncture therapies in this context.

OBJECTIVE

The objective of this review was to assess the efficacy and safety of acupuncture therapies as complementary or alternative treatments for pain relief in patients with PID.

METHOD

A comprehensive search was conducted in eight databases from inception to February 20, 2023: PubMed, Embase, Web of Science, the Cochrane Library, China National Knowledge Infrastructure, Wanfang Database, VIP Database, and Chinese Biomedical Literature Database. Randomized controlled trials (RCTs) investigating acupuncture therapies as complementary or additional treatments to routine care were identified. Primary outcomes were pain intensity scores for abdominal or lumbosacral pain. The Cochrane risk of bias criteria was applied to assess the methodological quality of the included trials. The Grading of Recommendations, Assessment, Development, and Evaluations (GRADE) system was used to evaluate the quality of evidence. Data processing was performed using RevMan 5.4.

RESULT

This systematic review included twelve trials comprising a total of 1,165 patients. Among these, nine trials examined acupuncture therapies as adjunctive therapy, while the remaining three did not. Meta-analyses demonstrated that acupuncture therapies, whether used alone or in combination with routine treatment, exhibited greater efficacy in relieving abdominal pain compared to routine treatment alone immediately after the intervention (MD: -1.32; 95% CI: -1.60 to -1.05; P < 0.00001). The advantage of acupuncture therapies alone persisted for up to one month after the treatment (MD: -1.44; 95% CI: -2.15 to -0.72; P < 0.0001). Additionally, acupuncture therapies combined with routine treatment had a more pronounced effect in relieving lumbosacral pain after the intervention (MD: -1.14; 95% CI: -2.12 to -0.17; P < 0.00001) in patients with PID. The incidence of adverse events did not increase with the addition of acupuncture therapies (OR: 0.56; 95% CI: 0.21 to 1.51; P = 0.25). The findings also indicated that acupuncture therapies, as a complementary treatment, could induce anti-inflammatory cytokines, reduce pro-inflammatory cytokines, alleviate anxiety, and improve the quality of life in patients with PID.

CONCLUSION

Our findings suggest that acupuncture therapies may effectively reduce pain intensity in the abdomen and lumbosacral region as complementary or alternative treatments, induce anti-inflammatory cytokines, decrease pro-inflammatory cytokines, alleviate anxiety, and enhance the quality of life in patients with PID, without increasing the occurrence of adverse events. However, due to the low quality of the included trials, the conclusion should be interpreted with caution, highlighting the need for further high-quality trials to establish more reliable conclusions.

What is the analgesic range of acupuncture stimulus for treating acute pain?

Introduction

Since the analgesic effect of acupuncture stimulation is derived from different mechanisms depending on the type of pain, it is important to know which acupuncture points to stimulate. In this study, to confirm the effect of acupuncture stimulation on acute pain from a neurological point of view, somatosensory evoked potential and sensory threshold changes were evaluated to identify the nerve range that is affected by acupuncture stimulation on LI4 (Hapgok acupuncture point, of the radial nerve) during acute pain.

Methods

The subjects were 40 healthy men and women aged 19-35 years. The study was designed as a randomly controlled, crossover trial with acupuncture stimulation at LI4 as the intervention. The washout period for acupuncture stimulation was 2 weeks, and the subjects were divided into two groups, i.e., an acupuncture stimulation group and a nonstimulation group, with 10 men and 10 women in each group. Somatosensory evoked potential measurement was carried out for 5 min by alternately applying 2 HZ-pulse electrical stimulation to the thumb and the little finger of the hand acupunctured with a 64-channel electroencephalogram. The verbal rating scale was used before and after each acupuncture stimulation session.

Result and discussion

The results of the study confirmed that the somatosensory evoked potential amplitude value of the thumb was significantly decreased and that the intensity of sensory stimulation corresponding to a verbal rating scale score of 6 was significantly increased only in the thumb after acupuncture stimulation. Therefore, the results show that acupuncture treatment for acute pain is more effective when direct acupuncture stimulation is applied to the painful area.

Phosphoproteomic Profiling of Rat's Dorsal Root Ganglia Reveals mTOR as a Potential Target in Bone Cancer Pain and Electro-Acupuncture's Analgesia

Bone cancer pain (BCP) is a clinical refractory mixed pain involving neuropathic and inflammatory pain, with the underlying mechanisms remaining largely unknown. Electro-acupuncture (EA) can partly alleviate BCP according to previous research. We aim to explore the proteins and major pathways involved in BCP and EA treatment through phosphoproteomic profiling. BCP rat model was built by tibial inoculation of MRMT-1 mammary gland carcinoma cells. Mechanical hyperalgesia determined by paw withdrawal thresholds (PWTs) and bone destruction manifested on the radiographs confirmed the success of modeling, which were attenuated by EA treatment. The differentially expressed phosphorylated proteins (DEPs) co-regulated by BCP modeling and EA treatment in rat dorsal root ganglions (DRGs) were analyzed through PEX100 Protein microarray. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that DEPs were significantly enriched in mammalian target of rapamycin (mTOR) signaling pathway. The phosphorylations of mTOR at Ser2448 and Thr2446 were increased in BCP and downregulated by EA. In addition, the phosphorylation of S6K and Akt, markers of the mTOR complex, were also increased in BCP and downregulated by EA. Inhibition of mTOR signaling alleviated the PWTs of BCP rats, while the mTOR agonist impaired the analgesic effect of EA. Thus, our study provided a landscape of protein phosphorylation changes in DRGs of EA-treated BCP rats and revealed that mTOR signaling can be potentially targeted to alleviate BCP by EA treatment.

Islet-cell autoantigen 69 mediates the antihyperalgesic effects of electroacupuncture on inflammatory pain by regulating spinal glutamate receptor subunit 2 phosphorylation through protein interacting with C-kinase 1 in mice

Supplemental Digital Content is Available in the Text.

A clear role of ICA69 in mediating the antihyperalgesic effects of electroacupuncture was confirmed, and the ICA69-PICK1-GluR2 molecular mechanism to explain these effects is proposed.

Electroacupuncture (EA) is widely used in clinical settings to reduce inflammatory pain. Islet-cell autoantigen 69 (ICA69) has been reported to regulate long-lasting hyperalgesia in mice. ICA69 knockout led to reduced protein interacting with C-kinase 1 (PICK1) expression and increased glutamate receptor subunit 2 (GluR2) phosphorylation at Ser880 in spinal dorsal horn. In this study, we evaluated the role of ICA69 in the antihyperalgesic effects of EA and the underlying mechanism through regulation of GluR2 and PICK1 in spinal dorsal horn. Hyperalgesia was induced in mice with subcutaneous plantar injection of complete Freund adjuvant (CFA) to cause inflammatory pain. Electroacupuncture was then applied for 30 minutes every other day after CFA injection. When compared with CFA group, paw withdrawal frequency of CFA+EA group was significantly decreased. Remarkable increases in Ica1 mRNA expression and ICA69 protein levels on the ipsilateral side were detected in the CFA+EA group. ICA69 expression reached the peak value around day 3. More importantly, ICA69 deletion impaired the antihyperalgesic effects of EA on GluR2-p, but PICK1 deletion could not. Injecting ICA69 peptide into the intrathecal space of ICA69-knockout mice mimicked the effects of EA analgesic and inhibited GluR2-p. Electroacupuncture had no effects on the total protein of PICK1 and GluR2. And, EA could increase the formation of ICA69-PICK1 complexes and decrease the amount of PICK1-GluR2 complexes. Our findings indicate that ICA69 mediates the antihyperalgesic effects of EA on CFA-induced inflammatory pain by regulating spinal GluR2 through PICK1 in mice.

Peripheral ionotropic glutamate receptors contribute to Fos expression increase in the spinal cord through antidromic electrical stimulation of sensory nerves

Previous studies have shown that peripheral ionotropic glutamate receptors are involved in the increase in sensitivity of a cutaneous branch of spinal dorsal ramus (CBDR) through antidromic electrical stimulation (ADES) of another CBDR in the adjacent segment. CBDR in the thoracic segments run parallel to each other and no synaptic contact at the periphery is reported. The present study investigated whether the increased sensitivity of peripheral sensory nerves via ADES of a CBDR induced Fos expression changes in the adjacent segments of the spinal cord. Fos expression increased in the T8 - T12 segments of the spinal cord evoked by ADES of the T10 CBDR in rats. The increased Fos expression in the T11 and T12, but not T8 - T10 spinal cord segments, was significantly blocked by local application of either N-methyl-D-aspartate (NMDA) receptor antagonist dizocilpine maleate (MK-801) or non-NMDA receptor antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX) into the receptive field of T11 CBDR. The results suggest that endogenous glutamate released by ADES of sensory nerve may bind to peripheral ionotropic glutamate receptors and activate adjacent sensory nerve endings to increase the sensitivity of the spinal cord. These data reveal the potential mechanisms of neuron activation in the spinal cord evoked by peripheral sensitization.

Differential involvement of ipsilateral and contralateral spinal cord astrocyte D-serine in carrageenan-induced mirror-image pain: role of σ1 receptors and astrocyte gap junctions

BACKGROUND AND PURPOSE

Although we have recently demonstrated that spinal astrocyte gap junctions mediate the development of mirror-image pain (MIP), it is still unclear which astrocyte-derived factor is responsible for the development of MIP and how its production is controlled. In the present study, we focused on the role of ipsilateral versus contralateral D-serine in the development of MIP and investigated the possible involvement of σ1 receptors and gap junctions in astrocyte D-serine production.

EXPERIMENTAL APPROACH

Following carrageenan injection, mechanical allodynia was tested at various time points to examine the effect of individual drugs. Immunohistochemistry and Western blot analyses were performed to clarify the expression levels of spinal D-serine, serine racemase, σ1 receptors and connexin 43.

KEY RESULTS

The expression of ipsilateral D-serine was up-regulated during the early phase of inflammation, while contralateral D-serine increased during the later phase of inflammation. The pharmacological inhibition of D-serine during the early phase blocked the development of both ipsilateral and contralateral mechanical allodynia. However, the inhibition of D-serine during the later phase of inflammation blocked contralateral, but not ipsilateral mechanical allodynia. Furthermore, the inhibition of σ1 receptors during the earlier phase of inflammation inhibited the increase in ipsilateral D-serine. Conversely, the blockade of astrocyte gap junctions suppressed the up-regulation of contralateral D-serine during the later phase of inflammation.

CONCLUSION AND IMPLICATIONS

Spinal astrocyte D-serine plays an important role in the development of mirror-image pain. Furthermore, σ1 receptors and astrocyte gap junction signalling mediate ipsilateral and contralateral D-serine production respectively.

Electroacupuncture Inhibits the Activation of p38MAPK in the Central Descending Facilitatory Pathway in Rats with Inflammatory Pain

The mitogen-activated protein kinases (MAPKs), especially p38MAPK, play a pivotal role in chronic pain. Electroacupuncture (EA) relieves inflammatory pain underlying the descending pathway, that is, the periaqueductal gray (PAG), the rostral ventromedial medulla (RVM), and the spinal cord dorsal horn (SCDH). However, whether EA antagonizes inflammatory pain through regulation of p38MAPK in this descending facilitatory pathway is unclear. Complete Freund's adjuvant (CFA) was injected into the hind paw of rats to establish inflammatory pain model. EA was administrated for 30 min at Zusanli and Kunlun acupoints at 0.5, 24.5, 48.5, and 72.5 h, respectively. The paw withdrawal threshold (PWT), paw edema, and Phosphor-p38MAPK-Immunoreactivity (p-p38MAPK-IR) cells were measured before (0 h) and at 1, 3, 5, 7, 25, and 73 h after CFA or saline injection. EA increased PWT at 1, 3, 25, and 73 h and inhibited paw edema at 25 and 73 h after CFA injection. Moreover, the increasing number of p-p38MAPK-IR cells which was induced by CFA was suppressed by EA stimulation in PAG and RVM at 3 and 5 h and in SCDH at 5, 7, 25, and 73 h. These results suggest that EA suppresses inflammation-induced hyperalgesia probably through inhibiting p38MAPK activation in the descending facilitatory pathway.

The endocannabinoid system, a novel and key participant in acupuncture's multiple beneficial effects

Acupuncture and its modified forms have been used to treat multiple medical conditions, but whether the diverse effects of acupuncture are intrinsically linked at the cellular and molecular level and how they might be connected have yet to be determined. Recently, an emerging role for the endocannabinoid system (ECS) in the regulation of a variety of physiological/pathological conditions has been identified. Overlap between the biological and therapeutic effects induced by ECS activation and acupuncture has facilitated investigations into the participation of ECS in the acupuncture-induced beneficial effects, which have shed light on the idea that the ECS may be a primary mediator and regulatory factor of acupuncture's beneficial effects. This review seeks to provide a comprehensive summary of the existing literature concerning the role of endocannabinoid signaling in the various effects of acupuncture, and suggests a novel notion that acupuncture may restore homeostasis under different pathological conditions by regulating similar networks of signaling pathways, resulting in the activation of different reaction cascades in specific tissues in response to pathological insults.

P2Y12 receptor-mediated activation of spinal microglia and p38MAPK pathway contribute to cancer-induced bone pain

Background

Cancer-induced bone pain (CIBP) is one of the most challenging clinical problems due to a lack of understanding the mechanisms. Recent evidence has demonstrated that activation of microglial G-protein-coupled P2Y₁₂ receptor (P2Y₁₂R) and proinflammatory cytokine production play an important role in neuropathic pain generation and maintenance. However, whether P2Y₁₂R is involved in CIBP remains unknown.

Methods

The purpose of this study was to investigate the role of P2Y₁₂R in CIBP and its molecular mechanisms. Using the bone cancer model inoculated with Walker 256 tumor cells into the left tibia of Sprague Dawley rat, we blocked spinal P2Y₁₂R through intrathecal administration of its selective antagonist MRS2395 (400 pmol/µL, 15 µL).

Results

We found that not only the ionized calcium-binding adapter molecule 1 (Iba-1)-positive microglia in the ipsilateral spinal cord but also mechanical allodynia was significantly inhibited. Furthermore, it decreased the phosphorylation of p38 mitogen-activated protein kinase (p38 MAPK) and the production of proinflammatory cytokines interleukin-1β (IL-1β) and interleukin-6 (IL-6), whereas it increased tumor necrosis factor-α (TNF-α).

Conclusion

Taken together, our present results suggest that microglial P2Y₁₂R in the spinal cord may contribute to CIBP by the activation of spinal microglia and p38MAPK pathway, thus identifying a potential therapeutic target for the treatment of CIBP.

Acupuncture for seasonal allergic rhinitis: a randomized controlled trial

BACKGROUND

Seasonal allergic rhinitis (SAR) is a common condition with relatively high prevalence in Australia. It causes a significant impact on sufferers' quality of life (QoL). Meta-analysis has shown that the efficacy of acupuncture for SAR is uncertain.

OBJECTIVE

To evaluate the efficacy and safety of 12 sessions of acupuncture treatment during 4 weeks for SAR in a randomized, subject- and assessor-blinded, sham-controlled trial conducted during the pollen seasons in 2009 through 2011 in Melbourne.

METHODS

Patients diagnosed with SAR and confirmed allergic to rye grass pollen were randomly allocated to receive real acupuncture (RA) or sham acupuncture (SA) treatment. RA was delivered manually, whereas SA involved superficial needling at non-acupoints without additional stimulation. Severity of SAR symptoms was the primary outcome measurement. Secondary outcomes were QoL, global change, SAR-related medication usage, and adverse events. Analysis of covariance using pollen count as a covariate was used to analyze outcome data.

RESULTS

A total of 175 participants were included in this trial. RA was significantly better than SA for decreasing SAR symptom severity (sneezing, mean difference -0.28, 95% confidence interval -0.51 to -0.05; itchiness of ears and palate, mean difference -0.40, 95% confidence interval -0.69 to -0.11) at the end of treatment and improving participants' QoL at the end of the treatment and follow-up phases. Furthermore, the acupuncture treatment was safe and well tolerated.

CONCLUSION

Four weeks of acupuncture treatment is a safe and effective option for clinical management of SAR in the Melbourne area for patients' symptom relief and QoL improvement.

Downregulation of Spinal G Protein-Coupled Kinase 2 Abolished the Antiallodynic Effect of Electroacupuncture

Acupuncture or electroacupuncture (EA) has been demonstrated to have a powerful antihypernociceptive effect on inflammatory pain. The attenuation of G protein-coupled receptor kinase 2 (GRK2) in spinal cord and peripheral nociceptor has been widely acknowledged to promote the transition from acute to chronic pain and to facilitate the nociceptive progress. This study was designed to investigate the possible role of spinal GRK2 in EA antiallodynic in a rat model with complete Freund's adjuvant (CFA) induced inflammatory pain. EA was applied to ST36 (“Zusanli”) and BL60 (“Kunlun”) one day after CFA injection. Single EA treatment at day 1 after CFA injection remarkably alleviated CFA induced mechanical allodynia two hours after EA. Repeated EA displayed significant antiallodynic effect from 2nd EA treatment and a persistent effect was observed during the rest of treatments. However, downregulation of spinal GRK2 by intrathecal exposure of GRK2 antisense 30 mins after EA treatment completely eliminated both the transient and persistent antiallodynic effect by EA treatment. These pieces of data demonstrated that the spinal GRK2 played an important role in EA antiallodynia on inflammatory pain.

Effect of electro-acupuncture stimulation of Ximen (PC4) and Neiguan (PC6) on remifentanil-induced breakthrough pain following thoracal esophagectomy

The clinical analgesic effect of electro-acupuncture (EA) stimulation (EAS) on breakthrough pain induced by remifentanil in patients undergoing radical thoracic esophagectomy, and the mechanisms were assessed. Sixty patients (ASAIII) scheduled for elective radical esophagectomy were randomized into three groups: group A (control) receiving a general anesthesia only; group B (sham) given EA needles at PC4 (Ximen) and PC6 (Neiguan) but no stimulation; and group C (EAS) electrically given EAS of the ipsilateral PC4 and PC6 throughout the surgery. The EAS consisting of a disperse-dense wave with a low frequency of 2 Hz and a high frequency of 20 Hz, was performed 30 min prior to induction of general anesthesia and continued through the surgery. At the emergence, sufentanil infusion was given for postoperative analgesia with loading dose of 7.5 μg, followed by a continuous infusion of 2.25 μg/h. The patient self-administration of sufentanil was 0.75 μg with a lockout of 15 min as needed. Additional breakthrough pain was treated with dezocine (5 mg) intravenously at the patient's request. Blood samples were collected before (T1), 2 h (T2), 24 h (T3), and 48 h (T4) after operation to measure the plasma β-EP, PGE2, and 5-HT. The operative time, the total dose of sufentanil and the dose of self-administration, and the rescue doses of dezocine were recorded. Visual Analogue Scale (VAS) scores at 2, 12, 24 and 48 h postoperatively and the incidence of apnea and severe hypotension were recorded. The results showed that the gender, age, weight, operative time and remifentanil consumption were comparable among 3 groups. Patients in EAS group had the lowest VAS scores postoperatively among the three groups (P<0.05). The total dose of sufentanil was 115±6.0 μg in EAS group, significantly lower than that in control (134.3±5.9 μg) and sham (133.5±7.0 μg) groups. Similarly, the rescue dose of dezocine was the least in EAS group (P<0.05) among the three groups. Plasma β-EP levels in EAS group at T3 (176.90±45.73) and T4 (162.96±35.00 pg/mL) were significantly higher than those in control (132.33±36.75 and 128.79±41.24 pg/mL) and sham (136.56±45.80 and 129.85±36.14 pg/mL) groups, P<0.05 for all. EAS could decrease the release of PGE2. Plasma PGE2 levels in EAS group at T2 and T3 (41±5 and 40±5 pg/mL respectively) were significantly lower than those in control (64±5 and 62±7 pg/mL) and sham (66±6 and 62±6 pg/mL) groups. Plasma 5-HT levels in EAS group at T2 (133.66±40.85) and T3 (154.66±52.49 ng/mL) were significantly lower than those in control (168.33±56.94 and 225.28±82.03) and sham (164.54±47.53 and 217.74±76.45 ng/mL) groups. For intra-group comparison, plasma 5-HT and PGE2 levels in control and sham groups at T2 and T3, and β-EP in EAS group at T3 and T4 were significantly higher than those at T1 (P<0.05); PGE2 and 5-HT levels in EAS group showed no significant difference among the different time points (P>0.05). No apnea or severe hypotension was observed in any group. It was concluded that intraoperative ipsilateral EAS at PC4 and PC6 provides effective postoperative analgesia for patients undergoing radical esophagectomy with remifentanil anesthesia and significantly decrease requirement for parental narcotics. The underlying mechanism may be related to stimulation of the release of endogenous β-EP and inhibition of inflammatory mediators (5-HT and PGE2).

Electroacupuncture attenuates mechanical allodynia by suppressing the spinal JNK1/2 pathway in a rat model of inflammatory pain

BACKGROUND

Electroacupuncture (EA) has a substantial analgesic effect on inflammatory pain induced by complete Freund's adjuvant (CFA). The activation of the c-Jun N-terminal kinase 1/2 (JNK1/2) signal transduction pathway in the spinal cord is associated with inflammatory pain. However, the relationship between EA's analgesic effect and the JNK1/2 signal transduction pathway in the inflammatory pain remain unclear. In the present study, we used the established rat model of CFA-induced inflammatory pain to investigate the role of the spinal JNK1/2 pathway in EA-mediated analgesia.

RESULTS

We observed a decrease in paw withdrawal thresholds and an increase in paw edema at 1 and 3 days after injecting CFA into the right hindpaw. CFA, 3 days after injection, upregulated expression of phospho-c-Jun N-terminal kinase1/2 (p-JNK1/2) protein and its downstream targets, the transcriptional regulators p-c-Jun and activator protein-1 (AP-1), as well as cyclooxygenase-2 (COX-2) and the transient receptor potential vanilloid 1 (TRPV1). EA significantly alleviated CFA-induced inflammatory pain. In addition, EA reduced p-JNK1/2 protein levels and COX-2 mRNA expressions, a degree of down-regulated p-c-Jun protein level and AP-1 DNA binding activity in the spinal dorsal horn of CFA-administered animals, but it had no effect on TRPV1 mRNA expression. Furthermore, EA and the JNK inhibitor SP600125 synergistically inhibited CFA-induced hyperalgesia and suppressed the COX-2 mRNA expression in the spinal dorsal horn.

CONCLUSIONS

Our findings indicate that EA alleviates inflammatory pain behavior, at least in part, by reducing COX-2 expression in the spinal cord via the JNK1/2 signaling pathway. Inactivation of the spinal JNK1/2 signal transduction pathway maybe the potential mechanism of EA's antinociception in the inflammatory pain model.

Activation of spinal neuregulin 1-ErbB2 signaling pathway in a rat model of cancer-induced bone pain

Current therapies for cancer-induced bone pain (CIBP) are still limited. Until recently, the molecular mechanisms underlying the spinal cell-mediated CIBP remain largely unknown. To better understand the role of spinal cells in CIBP, we investigated the role of spinal neuregulin1 (NRG1)‑ErbB2 signaling pathway in CIBP. In this study, a rat model of CIBP was established by intra-tibia inoculation of Walker 256 mammary gland carcinoma cells. Tibia bone destruction was evaluated using various methods of Walker 256 inoculation, radiobioassay and histological analysis. Pain-like behavior including thermal hyperalgesia and mechanical allodynia were determined by measuring paw withdrawal latency (PWL) and mechanical paw withdrawal thresholds (PWT). The expression level of mRNA or protein of target genes was examined by quantitative reverse transcription-polymerase chain reaction (qPCR) and western blot analysis, respectively. Bone destruction, as well as thermal hyperalgesia and mechanical allodynia, were observed at the 6th day following Walker 256 inoculation. A time-dependent increase in the levels of NRG1, ErbB2 and p-ErbB2 could be detected within three weeks after tumor cell injection. ErbB2 signaling inactivation by PD168393 treatment significantly attenuated pain-like behavior, associated with inhibition of Akt-1 and p38MAPK activation. Administration of exogenous NRG1 provoked pain-like behavior in rats by induction of activation of ErbB2, Akt-1 and p38MAPK, which could be blocked by ErbB2 inhibitor. Our results indicate that activation of NRG1‑ErbB2 signaling pathway plays a critical role in the induction of CIBP. Akt-1 and p38MAPK may be potent players involved in the NRG1-ErbB2 pathway in CIBP.

Mechanisms of acupuncture-electroacupuncture on persistent pain

In the last decade, preclinical investigations of electroacupuncture mechanisms on persistent tissue injury (inflammatory), nerve injury (neuropathic), cancer, and visceral pain have increased. These studies show that electroacupuncture activates the nervous system differently in health than in pain conditions, alleviates both sensory and affective inflammatory pain, and inhibits inflammatory and neuropathic pain more effectively at 2 to 10 Hz than at 100 Hz. Electroacupuncture blocks pain by activating a variety of bioactive chemicals through peripheral, spinal, and supraspinal mechanisms. These include opioids, which desensitize peripheral nociceptors and reduce proinflammatory cytokines peripherally and in the spinal cord, and serotonin and norepinephrine, which decrease spinal N-methyl-D-aspartate receptor subunit GluN1 phosphorylation. Additional studies suggest that electroacupuncture, when combined with low dosages of conventional analgesics, provides effective pain management which can forestall the side effects of often-debilitating pharmaceuticals.

Intervention of electroacupuncture on spinal p38 MAPK/ATF-2/VR-1 pathway in treating inflammatory pain induced by CFA in rats

Background

Previous studies have demonstrated that p38 MAPK signal transduction pathway plays an important role in the development and maintenance of inflammatory pain. Electroacupuncture (EA) can suppress the inflammatory pain. However, the relationship between EA effect and p38 MAPK signal transduction pathway in inflammatory pain remains poorly understood. It is our hypothesis that p38 MAPK/ATF-2/VR-1 and/or p38 MAPK/ATF-2/COX-2 signal transduction pathway should be activated by inflammatory pain in CFA-injected model. Meanwhile, EA may inhibit the activation of p38 MAPK signal transduction pathway. The present study aims to investigate that anti-inflammatory and analgesic effect of EA and its intervention on the p38 MAPK signal transduction pathway in a rat model of inflammatory pain.

Results

EA had a pronounced anti-inflammatory and analgesic effect on CFA-induced chronic inflammatory pain in rats. EA could quickly raise CFA-rat’s paw withdrawal thresholds (PWTs) and maintain good and long analgesic effect, while it subdued the ankle swelling of CFA rats only at postinjection day 14. EA could down-regulate the protein expressions of p-p38 MAPK and p-ATF-2, reduced the numbers of p-p38 MAPK-IR cells and p-ATF-2-IR cells in spinal dorsal horn in CFA rats, inhibited the expressions of both protein and mRNA of VR-1, but had no effect on the COX-2 mRNA expression.

Conclusions

The present study indicates that inhibiting the activation of spinal p38 MAPK/ATF-2/VR-1 pathway may be one of the main mechanisms via central signal transduction pathway in the process of anti-inflammatory pain by EA in CFA rats.

The anti-inflammatory effects of acupuncture and their relevance to allergic rhinitis: a narrative review and proposed model

Classical literature indicates that acupuncture has been used for millennia to treat numerous inflammatory conditions, including allergic rhinitis. Recent research has examined some of the mechanisms underpinning acupuncture's anti-inflammatory effects which include mediation by sympathetic and parasympathetic pathways. The hypothalamus-pituitary-adrenal (HPA) axis has been reported to mediate the antioedema effects of acupuncture, but not antihyperalgesic actions during inflammation. Other reported anti-inflammatory effects of acupuncture include an antihistamine action and downregulation of proinflammatory cytokines (such as TNF-α, IL-1β, IL-6, and IL-10), proinflammatory neuropeptides (such as SP, CGRP, and VIP), and neurotrophins (such as NGF and BDNF) which can enhance and prolong inflammatory response. Acupuncture has been reported to suppress the expression of COX-1, COX-2, and iNOS during experimentally induced inflammation. Downregulation of the expression and sensitivity of the transient receptor potential vallinoid 1 (TRPV1) after acupuncture has been reported. In summary, acupuncture may exert anti-inflammatory effects through a complex neuro-endocrino-immunological network of actions. Many of these generic anti-inflammatory effects of acupuncture are of direct relevance to allergic rhinitis; however, more research is needed to elucidate specifically how immune mechanisms might be modulated by acupuncture in allergic rhinitis, and to this end a proposed model is offered to guide further research.

Inhibition of Activity of GABA Transporter GAT1 by δ-Opioid Receptor

Analgesia is a well-documented effect of acupuncture. A critical role in pain sensation plays the nervous system, including the GABAergic system and opioid receptor (OR) activation. Here we investigated regulation of GABA transporter GAT1 by δOR in rats and in Xenopus oocytes. Synaptosomes of brain from rats chronically exposed to opiates exhibited reduced GABA uptake, indicating that GABA transport might be regulated by opioid receptors. For further investigation we have expressed GAT1 of mouse brain together with mouse δOR and μOR in Xenopus oocytes. The function of GAT1 was analyzed in terms of Na⁺-dependent [³H]GABA uptake as well as GAT1-mediated currents. Coexpression of δOR led to reduced number of fully functional GAT1 transporters, reduced substrate translocation, and GAT1-mediated current. Activation of δOR further reduced the rate of GABA uptake as well as GAT1-mediated current. Coexpression of μOR, as well as μOR activation, affected neither the number of transporters, nor rate of GABA uptake, nor GAT1-mediated current. Inhibition of GAT1-mediated current by activation of δOR was confirmed in whole-cell patch-clamp experiments on rat brain slices of periaqueductal gray. We conclude that inhibition of GAT1 function will strengthen the inhibitory action of the GABAergic system and hence may contribute to acupuncture-induced analgesia.

Electroacupuncture alleviates affective pain in an inflammatory pain rat model

Pain has both sensory-discriminative and emotional-affective dimensions. Previous studies demonstrate that electroacupuncture (EA) alleviates the sensory dimension but do not address the affective. An inflammatory pain rat model, produced by a complete Freund adjuvant (CFA) injection into the hind paw, was combined with a conditioned place avoidance (CPA) test to determine whether EA inhibits spontaneous pain-induced affective response and, if so, to study the possibility that rostral anterior cingulate cortex (rACC) opioids underlie this effect. Male Sprague-Dawley rats (250-275 g, Harlan) were used. The rats showed place aversion (i.e. affective pain) by spending less time in a pain-paired compartment after conditioning than during a preconditioning test. Systemic non-analgesic morphine (0.5 and 1.0 mg/kg, i.p.) inhibited the affective reaction, suggesting that the affective dimension is underpinned by mechanisms different from those of the sensory dimension of pain. Morphine at 0.5 and at 1 mg/kg did not induce reward. Rats given EA treatment before pain-paired conditioning at GB 30 showed no aversion to the pain-paired compartment, indicating that EA inhibited the affective dimension. EA treatment did not produce reward or aversive effect. Intra-rACC administration of D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr amide (CTOP), a selective mu opioid receptor antagonist, but not norbinaltorphimine (nor-BNI), a selective kappa opioid receptor antagonist, blocked EA inhibition of the affective dimension. These data demonstrate that EA activates opioid receptors in the rACC to inhibit pain-induced affective responses and that EA may be an effective therapy for both the sensory-discriminative and the affective dimensions of pain.

Peripheral nerve injury decreases the expression of metabolic glutamate receptor 7 in dorsal root ganglion neurons

Group II and III metabolic glutamate receptors (mGluRs) are responsible for the glutamate-mediated postsynaptic excitation of neurons. Previous pharmacological evidences show that activation of mGluR7 could inhibit nociceptive reception. However, the distribution and expression patterns of mGluR7 after peripheral injury remain unclear. Herein we found that mGluR7 was expressed in the rat peptidergic dorsal root ganglion (DRG) neurons and large neurons, but rarely in isolectin B4 positive neurons. Sciatic nerve ligation experiment showed that mGluR7 was anterogradely transported from cell body to the peripheral site. Furthermore, after peripheral nerve injury, mGluR7 expression was down-regulated in both peptidergic and large DRG neurons. Our work suggests that mGluR7 might be involved in the regulation of pathological pain after peripheral nerve injury.

Electroacupuncture Confers Antinociceptive Effects via Inhibition of Glutamate Transporter Downregulation in Complete Freund's Adjuvant-Injected Rats

When we evaluated changes of glial fibrillary acidic protein (GFAP) and two glutamate transporter (GTs) by immunohistochemistry, expression of GFAP showed a significant increase in complete Freund's adjuvant (CFA)-injected rats; however, this expression was strongly inhibited by electroacupuncture (EA) stimulation. Robust downregulation of glutamate-aspartate transporter (GLAST) and glutamate transporter-1 (GLT-1) was observed in CFA-injected rats; however, EA stimulation resulted in recovery of this expression. Double-labeling staining showed co-localization of a large proportion of GLAST or GLT-1 with GFAP. Using Western blot, we confirmed protein expression of two GTs, but no differences in the mRNA content of these GTs were observed. Because EA treatment resulted in strong inhibition of CFA-induced proteasome activities, we examined the question of whether thermal sensitivities and GTs expression could be regulated by proteasome inhibitor MG132. CFA-injected rats co-treated with EA and MG132 showed a significantly longer thermal sensitivity, compared with CFA-injected rats with or without MG132. Both EA and MG132 blocked CFA-induced GLAST and GLT-1 downregulation within the spinal cord. These results provide evidence for involvement of GLAST and GLT-1 in response to activation of spinal astrocytes in an EA antinociceptive effect. Antinociceptive effect of EA may be induced via proteasome-mediated regulation of spinal GTs.

Electroacupuncture inhibition of hyperalgesia in an inflammatory pain rat model: involvement of distinct spinal serotonin and norepinephrine receptor subtypes

BACKGROUND

Although acupuncture analgesia is well documented, its mechanisms have not been thoroughly clarified. We previously showed that electroacupuncture (EA) activates supraspinal serotonin- and norepinephrine-containing neurones that project to the spinal cord. This study investigates the involvement of spinal alpha(2)-adrenoceptors (α2-ARs) and 5-hydroxytryptamine (serotonin) receptors (5-HTRs) in EA effects on an inflammatory pain rat model.

METHODS

Inflammatory hyperalgesia was induced by injecting complete Freund's adjuvant (CFA, 0.08 ml) into the plantar surface of one hind paw and assessed by paw withdrawal latency (PWL) to a noxious thermal stimulus. The selective α2a-AR antagonist BRL-44408, α2b-AR antagonist imiloxan hydrochloride, 5-HT2B receptor (5-HT2BR) antagonist SB204741, 5-HT3R antagonist LY278584, or 5-HT1AR antagonists NAN-190 hydrobromide, or WAY-100635 were intrathecally administered 20 min before EA or sham EA, which was given 2 h post-CFA at acupoint GB30.

RESULTS

EA significantly increased PWL compared with sham [7.20 (0.46) vs 5.20 (0.43) s]. Pretreatment with α2a-AR [5.35 (0.45) s] or 5-HT1AR [5.22 (0.38) s] antagonists blocked EA-produced anti-hyperalgesia; α2b-AR, 5-HT2BR, and 5-HT3R antagonist pretreatment did not. Sham plus these antagonists did not significantly change PWL compared with sham plus vehicle, indicating that the antagonists had little effect on PWL. Immunohistochemical staining demonstrated that α2a-ARs are on primary afferents and 5-HT1ARs are localized in N-methyl-d-aspartic acid (NMDA) subunit NR1-containing neurones in the spinal dorsal horn.

CONCLUSIONS

The data show that α2a-ARs and 5-HT1ARs are involved in the EA inhibition of inflammatory pain and that the NMDA receptors are involved in EA action.

Comparison of the effects of carbamyl-beta-methylcholine chloride administered by intravenous, intramuscular and intra-acupuncture point injections

OBJECTIVE

To compare the effects of carbamyl-beta-methylcholine chloride (CMCC) administered by intra-acupuncture point injection (IAI), intramuscular injection (IMI), and intravenous injection (IVI), and to analyze the mechanisms.

METHODS

In the IAI group, CMCC was injected into the Zusanli acupoint (ST 36) immediately after 30-min stimulation by electro-acupuncture (EA) at the acupoints, and into the femoral vein and skeletal muscle in IVI and IMI groups, respectively. Intra-gastric pressure was detected. The plasma concentration of CMCC was measured at various times.

RESULTS

The gastric effect of CMCC in the IVI group was enhanced and attenuated more rapidly than in the other groups. In the IAI group, this effect was significantly stronger than that in the IMI group at 2 min and 15 min, but not significantly different between the two groups at 5 min and 30 min. Plasma concentration of CMCC in the IAI group was similar to that in the IVI group at 2 min, but higher than that in the IMI group. The concentration in the IAI group was higher than that in the IV group and similar to that in the IMI group at 5, 15 and 30 min, indicating rapid increase and slower reduction of the plasma concentration of the drug in the IAI group. There was a positive correlation between the plasma concentration of CMCC and intragastric pressure in all groups.

CONCLUSION

The effect of IAI with CMCC was stronger than that of IMI and longer-lasting than that of IVI, which correlated with the blood concentration of CMCC.

Effects of Electroacupuncture at BL60 on Formalin-Induced Pain in Rats

Acupuncture was used to treat symptoms of pain in the ancient orient. The present study was conducted to determine the effects of electroacupuncture (EA) at the BL60 acupoint on male Sprague-Dawley rats. Each rat received EA at BL60 acupoint before formalin injection. Behavioral responses were recorded using a video camera and c-Fos immunohistochemistry was performed thereafter. Treatment of EA at BL60 significantly inhibited flinching behavior and c-fos expression induced by formalin injection into the paw, compared to a control group. These results suggest that electroacupuncture at BL60 acupoint may be effective in relieving inflammatory pain.

N-Methyl-D-Aspartate Antagonist Inhibits NR-1 Subunit Phosphorylation of the Spinal N-Methyl-D-Aspartate Receptor Induced by Low Frequency Electroacupuncture

We investigated whether the 2 Hz electroacupuncture (EA) analgesia is associated with phosphorylation of N-methyl-D-aspartate receptor (NMDAR) NR-1 subunits and NMDAR antagonism in the lumbar spinal cord of rats. EA stimulation produced an increase of serine phosphorylation of NMDAR NR-1 subunits in the spinal cord as compared with normal conditions. However, the intrathecal injection of NMDAR antagonist D-2-amino-5-phosphonopentanoic acid significantly prevented serine phosphorylation of NMDAR NR-1 subunits induced by EA stimulation in the dorsal horn of spinal cord. These results indicate that EA analgesia by stimulation of peripheral nerves may be involved in an increase of NR-1 serine phosphorylation in the dorsal horn of the spinal cord.

Effects of Electroacupuncture on N-Methyl-D-aspartate Receptor-Related Signaling Pathway in the Spinal Cord of Normal Rats

This study examined the influence of the N-methyl-D-aspartate receptor (NMDAR) on the modulation of related spinal signaling after electroacupuncture (EA) treatment in normal rats. Bilateral 2 Hz EA stimulations (1-2-3.0 mA) were delivered at acupoints corresponding to Zusanli (ST36) and Sanyinjiao (SP6) in men for 30 min. Thermal sensitization was strongly inhibited by EA, but this analgesia was reduced by preintrathecal injection of the NMDAR antagonist, MK801. Phosphorylation of the NMDAR NR2B subunit, cAMP response element-binding protein (CREB), and especially phosphatidylinositol 3-kinase (PI3K) were significantly induced by EA. However, these marked phosphorylations were not observed in MK801-pretreated rats. EA analgesia was reduced by preintrathecal injection with the calcium chelators Quin2 and TMB8, similar to the results evident using MK801. Phosphorylation of PI3K and CREB induced by EA was also inhibited by TMB8. Calcium influx by NMDAR activation may play an important role in EA analgesia of normal rats through the modulation of the phosphorylation of spinal PI3K and CREB.

Electroacupuncture inhibits phosphorylation of spinal phosphatidylinositol 3-kinase/Akt in a carrageenan-induced inflammatory rat model

We investigated the changes of pain-related spinal signaling pathway after electroacupuncture (EA) stimulation in a carrageenan-induced rat model. EA stimulation (2Hz, 1mA) was needle-delivered for 30 min at acupoints corresponding to Zusanli and Sanyinjiao 3 h after carrageenan injection. Thermal and mechanical sensitivity of the hindpaw induced by carrageenan was strongly inhibited by EA stimulation. Phosphorylation of extracellular signal-regulated kinase, phosphatidylinositol 3-kinase (PI3K), Akt, and cAMP response element-binding protein (CREB) were examined in the L4-5 segments of the spinal cord by Western blot analysis 4h and 5h after carrageenan injection. Phosphorylation of Akt and especially PI3K were significantly induced by carrageenan-induction, but these expressions were markedly inhibited by EA stimulation. CREB phosphorylation showed a similar, but insignificant, pattern as like PI3k/Akt. Immunohistochemical analyses confirmed that phosphorylation of PI3K and Akt showed a similar pattern as Western blotting and were observed in most neurons and a few astrocytes. EA and PI3K inhibitor synergistically inhibited carrageenan-induced hyperalgesia. These results reveal that both neuronal PI3K and Akt may play an important role in EA-induced antinociception via inactivation in an inflammatory pain model.

The effects of opioid receptor antagonists on electroacupuncture-produced anti-allodynia/hyperalgesia in rats with paclitaxel-evoked peripheral neuropathy

Research supports the effectiveness of acupuncture for conditions such as chronic low back and knee pain. In a five-patient pilot study the modality also improved the symptoms of chemotherapy-induced neuropathic pain. Using an established rat model of paclitaxel-induced peripheral neuropathy, we evaluated the effect of electroacupuncture (EA) on paclitaxel-induced hyperalgesia and allodynia that has not been studied in an animal model. We hypothesize that EA would relieve the paclitaxel-induced mechanical allodynia and hyperalgesia, which was assessed 30 min after EA using von Frey filaments. Beginning on day 13, the response frequency to von Frey filaments (4-15 g) was significantly increased in paclitaxel-injected rats compared to those injected with vehicle. EA at 10 Hz significantly (P<0.05) decreased response frequency at 4-15 g compared to sham EA; EA at 100 Hz only decreased response frequency at 15 g stimulation. Compared to sham EA plus vehicle, EA at 10 Hz plus either a μ, δ, or κ opioid receptor antagonist did not significantly decrease mechanical response frequency, indicating that all three antagonists blocked EA inhibition of allodynia and hyperalgesia. Since we previously demonstrated that μ and δ but not κ opioid receptors affect EA anti-hyperalgesia in an inflammatory pain model, these data show that EA inhibits pain through different opioid receptors under varying conditions. Our data indicate that EA at 10 Hz inhibits mechanical allodynia/hyperalgesia more potently than does EA at 100 Hz. Thus, EA significantly inhibits paclitaxel-induced allodynia/hyperalgesia through spinal opioid receptors, and EA may be a useful complementary treatment for neuropathic pain patients.

Acupuncture alleviates the affective dimension of pain in a rat model of inflammatory hyperalgesia

Although studies demonstrate that electroacupuncture (EA) alleviates the sensory dimension of pain, they have not addressed EA's effect on the affective dimension. An inflammatory pain rat model, produced by a complete Freund adjuvant (CFA) injection into the hind paw, was combined with a conditioned place avoidance test to determine EA's effects and its underpinning mechanism on the affective dimension of pain. CFA-injected rats showed place aversion, i.e. the affective dimension of pain, by spending less time in a pain-paired compartment after conditioning than before, while saline-injected rats did not. CFA rats given EA treatment at GB30 before a post-conditioning test showed no aversion to the pain-paired compartment, indicating that EA inhibited the affective response. Intra-rostral anterior cingulate cortex (rACC) administration of a κ-, but not μ-opioid receptor antagonist, blocked EA action. These data demonstrate that EA activates opioid receptors in the rACC to inhibit the affective dimension of pain.

Involvement of spinal serotonin receptors in electroacupuncture anti-hyperalgesia in an inflammatory pain rat model

We previously showed that electroacupuncture (EA) activates medulla-spinal serotonin-containing neurons. The present study investigated the effects of intrathecal 5,7-dihydroxytryptamine creatinine sulfate, a selective neurotoxin for serotonergic terminals, the 5-hydroxytryptamine 1A receptor (5-HT1AR) antagonist NAN-190 hydrobromide and the 5-HT2C receptor (5-HT2CR) antagonist SB-242,084 on EA anti-hyperalgesia. EA was given twice at acupoint GB30 after complete Freund's adjuvant (CFA) injection into hind paw. CFA-induced hyperalgesia was measured by assessing hind paw withdrawal latency (PWL) to a noxious thermal stimulus 30 min post-EA. Serotonin depletion and the 5-HT1AR antagonist blocked EA anti-hyperalgesia; the 5-HT2CR antagonist did not. Immunohistochemical staining showed that spinal 5-HT1AR was expressed and that 5-HT2CR was absent in naive and CFA-injected animals 2.5 h post-CFA. These results show a correlation between EA anti-hyperalgesia and receptor expression. Collectively, the data show that EA activates supraspinal serotonin neurons to release 5-HT, which acts on spinal 5-HT1AR to inhibit hyperalgesia.

Rostral ventromedial medulla μ, but not κ, opioid receptors are involved in electroacupuncture anti-hyperalgesia in an inflammatory pain rat model

It has been reported that intracerebroventricular injection of a μ receptor antagonist blocked 2 but not 100Hz electroacupuncture (EA)-produced analgesia in an uninjured animal model. Because persistent pain changes neural response to external stimulation, we hypothesized that the mechanisms of EA anti-hyperalgesia may be different in persistent pain than in health. Hyperalgesia, decreased paw withdrawal latency (PWL) to a noxious thermal stimulus, was induced by subcutaneously injecting complete Freund's adjuvant (CFA) into the hind paws of rats. Selective antagonists against μ (CTOP: D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-ThrNH2, 6.25 nmol) and κ (Nor-BIN: nor-binaltorphimine, 10 nmol) opioid receptors were infused into the rostral ventromedial medulla (RVM) 10 min before a 30-min EA treatment at acupoint Huantiao (GB30) 1h 30 min post-CFA. PWL was measured before and 2.5 post-CFA. Both 10 Hz and 100 Hz EA-produced anti-hyperalgesia were blocked by intra-RVM μ, but not κ, receptor antagonists. Double immunofluorescence staining demonstrated that μ receptor-containing neurons were GABAnergic and that GABAa receptor-containing neurons were serotonergic in the RVM. The results demonstrated an involvement of RVM μ, but not κ, receptors in EA-produced anti-hyperalgesia. In summary, EA may induce release of endogenous endomorphins that activate μ opioid receptors in GABAnergic neurons to suppress the release of GABA. This removes the tonic inhibition of GABA on serotonergic neurons in the RVM, and activation of these serotonergic neurons inhibits pain. EA may be used as complementary treatment for inflammatory pain.

Peripheral muscarinic receptors mediate the anti-inflammatory effects of auricular acupuncture

BACKGROUND

The cholinergic and opioid systems play important roles in modulating inflammation. This study tests whether auricular acupuncture (AA) produces anti-inflammatory effects via opioid and peripheral cholinergic receptors in a rat model.

METHODS

Rats were anesthetized with chloral hydrate and inflammation was induced by intraplantar injection of carrageenan. Electroacupuncture was performed at auricular points bilaterally. The severity of inflammation was assessed using changes in paw volume and thermal and mechanical pain thresholds of the rats during recovery from anesthesia.

RESULTS

Electroacupuncture at selected auricular acupoints significantly reduced paw edema and mechanical hyperalgesia, with no significant effect on thermal hyperalgesia. The anti-edematous and analgesic effects of AA were abolished by blockade of peripheral cholinergic muscarinic receptors with methyl atropine. Blockade of local muscarinic receptors at the inflamed site with a small dose of atropine also antagonized the anti-edematous effect of AA. By contrast, systemic opioid receptor blockade with naloxone did not antagonize the anti-inflammatory effects of AA.

CONCLUSION

This study discovers a role of peripheral muscarinic receptors in mediating the anti-inflammatory effects of AA. The cholinergic muscarinic mechanism appears to be more important than the opioid mechanism in the anti-inflammatory action of AA.

Electroacupuncture reduces neuroinflammatory responses in symptomatic amyotrophic lateral sclerosis model

Amyotrophic lateral sclerosis (ALS) is a paralyzing disorder that is characterized by the progressive degeneration and death of motor neurons. Acupuncture or electroacupuncture (EA) has been used for the treatment of various conditions including osteoarthritis, asthma, and other types of chronic pain conditions. It has been hypothesized that acupuncture exerts anti-inflammatory and anti-nociceptive effects on inflammatory reactions processes. The purpose of this study was to determine whether acupuncture at a specific acupoint could produce anti-inflammatory responses and suppress motor neuron loss in the hG93ASOD1 mouse, commonly used as a model for inherited ALS. We delivered EA at the Zusanli (ST36) acupuncture point in the symptomatic hSOD1G93A animal model. The EA-treated mutant hSOD1 transgenic mice showed decreases in microglial cell activity and TNF-alpha expression in the spinal cord and brain stem. Furthermore, EA significantly improved motor activity compared to the control group and reduced neuronal cell loss in hSOD1G93A mice. Our research suggests a potential functional link between EA therapy and anti-neuroinflammatory response in an ALS animal model.

Involvement of intracellular calcium on the phosphorylation of spinal N-methyl-D-aspartate receptor following electroacupuncture stimulation in rats

This study examined the role of the intracellular calcium chelator, bis-(2-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid (BAPTA), in modulating the phosphorylation of the spinal N-methyl-d-aspartate receptor (NMDAR) NR1 and NR2B subunits after 2Hz electroacupuncture (EA) in rats. The level of EA analgesia was reduced by an intraperitoneal injection of BAPTA at a higher dose after terminating EA stimulation. At 60min after the EA treatment, the total number of c-fos-immunolabeled neurons in each region of the dorsal horn in lumbar segments (L4-5) was decreased by the BAPTA injection, particularly in the Nucleus proprius. The BAPTA injection decreased significantly the mean integrated optical density of phosphorylated NR1 subunit in the superficial laminae and neck region, and the phosphorylated NR2B subunit in the superficial laminae. Western blot analyses confirmed decreased levels of both phosphorylated subunits. In conclusion, intracellular calcium may play an important role in low-frequency EA analgesia by modulating the phosphorylation state of the spinal NMDAR subunits.

Contralateral electroacupuncture pretreatment suppresses carrageenan-induced inflammatory pain via the opioid-mu receptor

Acupuncture has been used to treat various clinical diseases in Eastern medicine. To investigate the analgesic effect of electroacupuncture (EA) pretreatment on carrageenan-induced inflammatory pain, we studied on the effect of EA parameters on an animal model of acute arthritic pain. Pretreatment with 1 mA, 10 Hz EA prior to carrageenan injection under halothane anesthesia suppressed carrageenan-induced pain. Interestingly, EA stimulation of the 'Zu-San-Li' (ST36) acupuncture point (1 mA, 10 Hz) contralateral to the site of the carrageenan injection in the rat synovial cavity produced significantly greater improvement of the weight-bearing force compared with EA stimulation of the 'San-Yin-Jiao' acupuncture point. To determine how ST36 EA treatment suppresses carrageenan-induced inflammatory pain, we examined the effect of a mu opioid receptor antagonist on ST36 EA-induced analgesia. The selective antagonist of the mu opioid receptor (OR) significantly suppressed contralateral ST36 EA-induced analgesia against carrageenan-induced inflammation. These results suggested that the analgesic effect mediated by the mu OR during low-frequency contralateral EA pretreatment has an anti-nociceptive action against inflammatory pain and that it may provide a potential strategy to treat inflammatory arthritic pain.

NMDA NR2A and NR2B receptors in the rostral anterior cingulate cortex contribute to pain-related aversion in male rats

NMDA receptors, which are implicated in pain processing, are highly expressed in forebrain areas including the anterior cingulate cortex (ACC). The ACC has been implicated in the affective response to noxious stimuli. Using a combination of immunohistochemical staining, Western blot, electrophysiological recording and formalin-induced conditioned place avoidance (F-CPA) rat behavioral model that directly reflects the affective component of pain, the present study examined formalin nociceptive conditioning-induced changes in the expressions of NMDA receptor subunits NR1, NR2A, and NR2B in the rostral ACC (rACC) and its possible functional significance. We found that unilateral intraplantar (i.pl.) injection of dilute formalin with or without contextual conditioning exposure markedly increased the expressions of NMDA receptor subunits NR2A and NR2B but not of NR1 in the bilateral rACC. NMDA-evoked currents in rACC neurons were significantly greater in formalin-injected rats than in naïve or normal saline-injected rats. Selectively blocking either NR2A or NR2B subunit in the rACC abolished the acquisition of F-CPA and formalin nociceptive conditioning-induced Fos expression, but it did not affect formalin acute nociceptive behaviors and non-nociceptive fear stimulus-induced CPA. These results suggest that both NMDA receptor subunits NR2A and NR2B in the rACC are critically involved in pain-related aversion. Thus, a new strategy targeted at NMDA NR2A or NR2B subunit might be raised for the prevention of pain-related emotional disturbance.

Pre-emptive anti-hyperalgesic effect of electroacupuncture in carrageenan-induced inflammation: role of nitric oxide

Central sensitization theory has been defined as pivotal for understanding the excitability changes in central neurons following peripheral inflammation or neuropathic injury. Considerable evidence has demonstrated that activation of the N-methyl-D-aspartate (NMDA) subtype of glutamate receptors and subsequent nitric oxide (NO) production are the key in these changes. Consequently, neuromodulator drugs have been developed during the last decades. The electroacupuncture (EA) that acts as biochemical modulator in the spinal horn cord would prevent these changes. The aim of this study was to determine the thermal anti-hyperalgesic effect of EA (10 Hz, 3 mA) and its combination with L-NAME as nitric oxide synthase (NOS) inhibitor in carrageenan-induced hyperalgesia in rats. Also, it investigated the changes in the plasmatic concentrations of NO metabolites. Moreover, the EA combination with sub-effective dose of ketamine as a NMDA antagonist was tested. The EA pre-treatment conducted in unsedated, unrestrained and conscious animals showed a thermal anti-hyperalgesic effect in correspondence with plasmatic increase of NO metabolites. The L-NAME (30 mg/kg) pre-administration decreased significantly the plasmatic concentrations of NO(2)(-)/NO(3)(-) and suppressed the anti-hyperalgesic effect of EA. The combination of EA with ketamine enhanced the anti-hyperalgesic effect. These data constitute the first report that suggested the participation, at least in part, of the L-arginine-NOS-NO-GMPc pathway activation in anti-hyperalgesic effect of EA in carrageenan-induced inflammation model.