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Objective: To observe the expression of GABA A receptor mRNA in different brain regions of the central nervous system in chronic inflammatory pain rats and the intervention effect of electroacupuncture (EA)., Methods: A total of 48 SPF male SD rats were randomly divided into a blank control group, a model control group, an EA group and a sham EA group, 12 rats in each group. The model of chronic inflammatory pain was established by injecting Freund's complete adjuvant into the foot. The EA group was treated with EA 28 days after the model establishment. The "Housanli" (ST 36) and "Kunlun" (BL 60) were selected and treated with dilatational wave, 2 Hz/100 Hz in frequency, 0.5-1.5 mA for 30 min; EA was given only once. In the sham EA group, the same acupoints were selected but the needles were only inserted into subcutaneous area; EA was connected for 30 min without electrical stimulation. The behavior changes of mechanical pain threshold and thermal pain threshold before model establishment, 1 day, 3 days, 7 days, 14 days, 21 days and 28 days after the model establishment as well as emotional behavior 29 days after the model establishment were observed; the relative expressions of GABA A receptor mRNA in anterior cingulate cortex, amygdala and hypothalamus were observed., Results: Compared with the blank control group, the change rates of mechanical pain threshold and thermal pain threshold in the model control group were decreased significantly 1 day, 3 days, 7 days, 14 days, 21 days, 28 days after model establishment ( P <0.01); 29 days after model establishment, the movement distance and staying time in the central area of open field test in the model control group were decreased significantly ( P <0.05). After EA intervention, compared with the model control group and the sham EA group, the change rates of mechanical pain threshold and thermal pain threshold, as well as the movement distance and the staying time of central area were significantly increased in the EA group ( P <0.01, P <0.05). Twenty-nine days after model establishment, the expression of GABA A receptor mRNA in anterior cingulate cortex and hypothalamus was not significantly different among all groups ( P >0.05). Compared with the blank control group, the expression of GABA A receptor mRNA in the amygdala was decreased significantly in the model control group ( P <0.01); compared with the model control group and the sham EA group, the expression of GABA A receptor mRNA in amygdala was increased after intervention in the EA group ( P <0.01)., Conclusion: Single treatment of EA could significantly increase the mechanical pain threshold and thermal pain threshold, improve abnormal emotional behavior in rats with chronic inflammatory pain, which may be related to the increasing of expression of GABA A receptor mRNA in the amygdala.

The aim was to observe the analgesic effect of Fengshi Qutong Capsules(FSQTC) on chronic inflammatory pain in mice, and investigate its effect on p-ERK/COX-2 signal molecular activity. A model of chronic inflammatory pain was induced in mice by complete Freund's adjuvant(CFA). The mice were divided into normal control group, model group, model+FSQTC 0.3, 0.6 and 1.2 g·kg~(-1 )groups, model+positive control drug ibuprofen(IBP, 0.34 mg·kg~(-1)·d~(-1)) group, and normal control+ FSQTC 1.2 g·kg~(-1)group. FSQTC or IBP was given once a day by oral administration. Standard Von Frey fiber was used to evaluate the mechanical pain threshold, and the acetone stimulation was used to induce inflammatory plantar and observe the cold pain reaction scores. The mechanical pain threshold and cold pain reaction scores were observed before administration and 1, 2, 3, 4, 6 h after administration on the first day, as well as 3 h after administration on the 3 rd to 7 th day. The protein levels of PGE&#95;2, COXs-1,2 and p-ERK in the spinal cord of the inflammatory foot and lumbar 4-5 were detected by enzyme-linked immunosorbent assay, Western blot, immunohistochemistry and immunofluorescence. The results showed that the mechanical pain threshold of the model group decreased and the cold pain reaction score increased as compared with the normal group. FSQTC application could dose-dependently increase the mechanical pain threshold and decrease the cold pain reaction score. The effect lasted for 6 h, most significant at 3 h. The effect of ibuprofen was similar to that of the 0.6 g·kg~(-1) dose group. In addition, FSQTC could reduce the abnormally increased protein content of PGE&#95;2, COX-2 and p-ERK in the inflammatory foot and/or spinal cord of the model group, and the effect was most significant in middle and high dose groups. However, it had no effect on COX-1 in the inflammatory foot and spinal cord of mice. The results suggest that FSQTC has ob-vious analgesic effect on chronic inflammatory pain in mice, which may be related to inhibition of p-ERK/COX-2 signaling pathway.

Evidences reported that high mobility group box 1 (HMGB1) played a pivotal role in the modulation of chronic inflammatory pain. Celastrol, a bioactive component extracted from Tripterygium wilfordii Hook, possesses anti-inflammatory activity, but the underlying mechanism remains to be fully clarified. We aim to investigate whether HMGB1 in dorsal root ganglion (DRG) participates in the effect of celastrol on inflammatory pain. Complete Freund's adjuvant (CFA)-induced inflammatory pain rat model was used. Paw withdrawal latency (PWL) was detected to evaluate the effects of celastrol on CFA-evoked inflammatory pain. After application of celastrol (1mg/kg, i.p.) on day 1, 3, 7 and 14 post-CFA injection, the expression levels of HMGB1, NF-κB, some proinflammatory markers, GFAP and CD11b in DRG were determined by qRT-PCR and western blot analysis. These results showed that celastrol significantly suppressed HMGB1, NF-κB and IL-1β mRNA and protein expression in DRG and alleviated CFA-evoked thermal hyperalgesia. Furthermore, celastrol obviously inhibited COX-2 protein expression and down-regulated IL-6, IL-17, TNF-α, MCP-1, GFAP and CD11b mRNA levels in DRG of CFA rats. Collectively, the present study firstly provide evidences of the anti-inflammatory effect of celastrol via suppressing CFA-induced the activation of HMGB1/NF-κB signaling pathway in DRG, which maybe a potential therapeutic target for celastrol alleviating inflammatory pain., (Copyright © 2018 Elsevier B.V. All rights reserved.)

The analgesic effects of gastrodin (GAS), an active component derived from the Chinese herb Tian ma (Gastrodia elata Blume), on chronic inflammatory pain of mice and the involved molecular mechanisms were investigated. GAS significantly attenuated mice chronic inflammatory pain induced by hindpaw injection of complete Freund's adjuvant (CFA) and the accompanying anxiety-like behaviors. GAS administration reduced CFA-induced up-regulation of GluR1-containing α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, GluN2A- and GluN2B-containing N-methyl-d-aspartate (NMDA) receptors, and Ca 2+ /calmodulin-dependent protein kinase II-alpha (CaMKII-α) in the anterior cingulate cortex (ACC). The GluN2A and GluN2B subunits of NMDA receptors, the GluR1 type of AMPA receptor, and CaMKII-α are key molecules responsible for neuroplasticity involved in chronic pain and the accompanying anxiety. Moreover, GAS administration reduced the activation of astrocyte and microglia and the induction of TNF-α and IL-6 in the ACC of the CFA-injected mice. Therefore, GAS administration relieved chronic pain, exerted anxiolytic effects by regulating neuroplasticity molecules, and attenuated the inflammatory response by reducing the induction of TNF-α and IL-6 in the ACC of the CFA-injected mice., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Pyruvate dehydrogenase kinases (PDK1-4) are mitochondrial metabolic regulators that serve as decision makers via modulation of pyruvate dehydrogenase (PDH) activity to convert pyruvate either aerobically to acetyl-CoA or anaerobically to lactate. Metabolic dysregulation and inflammatory processes are two sides of the same coin in several pathophysiological conditions. The lactic acid surge associated with the metabolic shift has been implicated in diverse painful states. In this study, we investigated the role of PDK-PDH-lactic acid axis in the pathogenesis of chronic inflammatory pain. Deficiency of Pdk2 and/or Pdk4 in mice attenuated complete Freund's adjuvant (CFA)-induced pain hypersensitivities. Likewise, Pdk2/4 deficiency attenuated the localized lactic acid surge along with hallmarks of peripheral and central inflammation following intraplantar administration of CFA. In vitro studies supported the role of PDK2/4 as promoters of classical proinflammatory activation of macrophages. Moreover, the pharmacological inhibition of PDKs or lactic acid production diminished CFA-induced inflammation and pain hypersensitivities. Thus, a PDK-PDH-lactic acid axis seems to mediate inflammation-driven chronic pain, establishing a connection between metabolism and inflammatory pain., Significance Statement: The mitochondrial pyruvate dehydrogenase (PDH) kinases (PDKs) and their substrate PDH orchestrate the conversion of pyruvate either aerobically to acetyl-CoA or anaerobically to lactate. Lactate, the predominant end product of glycolysis, has recently been identified as a signaling molecule for neuron-glia interactions and neuronal plasticity. Pathological metabolic shift and subsequent lactic acid production are thought to play an important role in diverse painful states; however, their contribution to inflammation-driven pain is still to be comprehended. Here, we report that the PDK-PDH-lactic acid axis constitutes a key component of inflammatory pain pathogenesis. Our findings establish an unanticipated link between metabolism and inflammatory pain. This study unlocks a previously ill-explored research avenue for the metabolic control of inflammatory pain pathogenesis., (Copyright © 2015 the authors 0270-6474/15/3514354-17$15.00/0.)

Chronic inflammatory pain is a common clinical disease that tends to be associated with negative emotions such as anxiety and depression. The anterior cingulate cortex (ACC) is involved in pain and pain-related anxiety, and γ-aminobutyric acid (GABA)-ergic interneurons play an important role in chronic pain and anxiety. Electroacupuncture (EA) has good analgesic and antianxiety effect, but the underlying mechanisms have not yet been fully elucidated. In this study, we established a chronic inflammatory pain model and observed that this model induced anxiety-like behaviors and decreased the numbers of parvalbumin (PV) and somatostatin (SOM) positive cells. Activation of PV but not SOM interneurons by chemogenetic techniques alleviated anxiety-like behaviors and pain sensation. EA treatment improved pain sensation, anxiety-like behaviors and increased the number of PV- positive cells in the ACC, but did not affect on the number of SOM-positive cells in the ACC. Moreover, specific inhibition of PV interneurons by chemogenetic methods reversed the analgesic and antianxiety effects of EA. These results suggest that EA ameliorates chronic inflammatory pain and pain-related anxiety by upregulating PV but not SOM interneurons in the ACC. [ABSTRACT FROM AUTHOR]

Yuanyuan Wu,1 Xinmiao Yao,2 Yongliang Jiang,1 Xiaofen He,1 Xiaomei Shao,1 Junying Du,1 Zui Shen,1 Qiaoying He,1 Jianqiao Fang1 1Department of Neurobiology and Acupuncture Research, The Third Clinical Medical College, Zhejiang Chinese Medical University, Hangzhou, 2The Third Affiliated Hospital of Zhejiang Chinese Medical University, Zhejiang, China Abstract: Pain is considered a multidimensional conscious experience that includes a sensory component and a negative affective-motivational component. The negative affective-motivational component of pain is different from the sensory component and amplifies the pain experience. Nowadays, a significant number of preclinical research groups have focused their attention on the affective symptoms of pain. In the present study, we investigated the pain aversion and anxiety-like behavior of the complete Freund’s adjuvant (CFA)-induced chronic pain model. CFA rats experienced spontaneous pain during pain-paired conditioning (pain aversion) and spontaneous pain produces an affective response (anxiety-like behavior). Moreover, pain aversion was gradually attenuated, while the anxiety-like behavior increased in 4 weeks. Therefore, although the negative effect (including pain aversion and anxiety) is always associated with hyperalgesia, the manifestations of negative effect may follow different time courses, which may influence the progress of primary disease. The findings illustrate that targeted therapy should focus on a specific aspect in different stages of pain. Our study emphasizes the necessity of using multiple tests to study pain comorbidities. Keywords: pain, pain aversion, pain affection, anxiety-like behavior, chronic inflammatory pain, rat

Pain is considered a multidimensional conscious experience that includes a sensory component and a negative affective-motivational component. The negative affective-motivational component of pain is different from the sensory component and amplifies the pain experience. Nowadays, a significant number of preclinical research groups have focused their attention on the affective symptoms of pain. In the present study, we investigated the pain aversion and anxiety like behavior of the complete Freund's adjuvant (CFA)-induced chronic pain model. CFA rats experienced spontaneous pain during pain-paired conditioning (pain aversion) and spontaneous pain produces an affective response (anxiety-like behavior). Moreover, pain aversion was gradually attenuated, while the anxiety-like behavior increased in 4 weeks. Therefore, although the negative effect (including pain aversion and anxiety) is always associated with hyperalgesia, the manifestations of negative effect may follow different time courses, which may influence the progress of primary disease. The findings illustrate that targeted therapy should focus on a specific aspect in different stages of pain. Our study emphasizes the necessity of using multiple tests to study pain comorbidities. [ABSTRACT FROM AUTHOR]

Nitric oxide (NO) is a gaseous molecule implicated both in vascular tone and nociceptive transmission. The capillary blood supply to the dorsal root ganglia (DRG) is unique because it is highly permeable to several low and high molecular-weight compounds. This anatomical situation leads to a potential role of endothelial nitric oxide synthase (eNOS) in inflammatory nociception, which is not well established. Therefore, we examined the role of eNOS in DRG in a murine chronic inflammatory pain model induced by complete Freund's adjuvant using L-N5-(1-iminoethyl)ornithine (L-NIO), a potent inhibitor of eNOS activity. Pain state was examined using a behavioral test. The expression of eNOS, platelet endothelial cell adhesion molecule-1 (CD31) and vascular endothelial growth factor (VEGF) was examined by immunofluorescence. In control animals, CD31 was detected in vessels; VEGF was localized both in vessels and neurons while a weak eNOS immunopositivity was detected in both vessels and in neurons. Under inflammatory pain conditions, eNOS, CD31 and VEGF immunopositivity increased. Administration of L-NIO significantly attenuated thermal hyperalgesia by 24 h and decreased eNOS activity and CD31 immunopositivity by 7 days. VEGF was unaffected. Our results show that eNOS plays a nociceptive role in the early phases of inflammation while in the later phases it may be involved in neurotrophic support. Copyright © 2012 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Abstract: The CatWalk gait analysis system has recently been suggested as a rapid and objective alternative method over the von Frey test to assess mechanical allodynia in chronic neuropathic pain models. Our results demonstrate that no correlation exists between the development of mechanical allodynia and changes in CatWalk-gait parameters in a chronic inflammatory pain model. Hence, the use of the CatWalk in assessment of experimental chronic pain is discussed. [Copyright &y& Elsevier]