Electroacupuncture Attenuates Neuropathic Pain and Comorbid Negative Behavior: The Involvement of the Dopamine System in the Amygdala

Neuropathic pain (NeuP) is an important clinical problem accompanying negative mood symptoms. Neuroinflammation in the amygdala is critically involved in NeuP, and the dopamine (DA) system acts as an important endogenous anti-inflammatory pathway. Electroacupuncture (EA) can improve the clinical outcomes in NeuP, but the underlying mechanisms have not been fully elucidated. This study was designed to assess the effectiveness of EA on pain and pain-related depressive-like and anxiety-like behaviors and explore the role of the DA system in the effects of EA. Male Sprague-Dawley rats were subjected to the chronic constrictive injury (CCI) model to induce NeuP. EA treatment was carried out for 30 min once every other day for 3 weeks. The results showed that CCI caused mechanical hyperalgesia and depressive and anxiety-like behaviors in rats and neuroinflammation in the amygdala, such as an increased protein level of TNFα and IL-1β and activation of astrocytes. EA treatment significantly improved mechanical allodynia and the emotional dysfunction induced by CCI. The effects of EA were accompanied by markedly decreased expression of TNFα, IL-1β, and glial fibrillary acid protein (GFAP) in the amygdala. Moreover, EA treatment reversed CCI-induced down-regulation of DA concentration, tyrosine hydroxylase (TH) expression, and DRD1 and DRD2 receptors. These results suggest that EA-ameliorated NeuP may possibly be associated with the DA system to inhibit the neuroinflammation in the amygdala.

Epigenetic modification of BDNF mediates neuropathic pain via miR-30a-3p/EP300 axis in CCI rats

Recent investigation of microRNAs on chronic pain has developed a breakthrough in neuropathic pain management. In the present study, decreased expression of miR-30a-3p was reported using qRT-PCR analysis and loss of miR-30a-3p promoted neuropathic pain progression in sciatic nerve chronic constrictive injury rats through determining the pain threshold. We predicted miR-30a-3p could target E-cadherin transcriptional activator (EP300) via bioinformatics analysis. Meanwhile, we found that brain-derived neurotrophic factor (BDNF) is involved in neuropathic pain. Here, we exhibited that EP300 epigenetically up-regulated BDNF via enhancing acetylated histone H3 and H4 on the promoter. For another, miR-30a-3p was able to modify the level of BDNF and acetylated histone H3 and H4. Loss of miR-30a-3p enhanced EP300 and BDNF colocalization in CCI rats. Subsequently, it was shown that increased EP300 induced neuropathic pain by an enhancement of neuronal BDNF level in vivo. To sum up, it was revealed that epigenetic modification of BDNF promoted neuropathic pain via EP300 induced by miR-30a-3p in CCI rats.

SIRT1 Mediates Neuropathic Pain Induced by Sciatic Nerve Chronic Constrictive Injury in the VTA-NAc Pathway

Background. Mounting evidence has shown that sirtuin 1 (SIRT1), a class III histone deacetylase, alleviated several types of neuropathic pain in the spinal cord and dorsal root ganglion and regulated some aberrant behaviors in the ventral tegmental area (VTA) and the nucleus accumbens (NAc). Methods. In this context, the effect of SIRT1 on neuropathic pain in the VTA-NAc pathway was investigated in the model of chronic constrictive injury (CCI). Results. SIRT1 was localized in the VTA neurons in naive mice. The expression of SIRT1 was decreased in the contralateral VTA of CCI mice. After microinjection of SRT1720 (an activator of SIRT1) in the contralateral VTA of CCI mice, the established thermal hyperalgesia was attenuated. However, it was further exacerbated by EX-527 (an inhibitor of SIRT1). The elevated level of acetyl-histone 3 was reduced by SRT1720 but further elevated by EX-527 in the contralateral VTA of CCI mice. The increased expression of Fos in both VTA and NAc was downregulated by SRT1720 but further upregulated by EX-527 in CCI mice. Conclusions. The discovery of the effect of SIRT1 on neuropathic pain in the VTA represents an important step forward in understanding the analgesic mechanisms of the VTA-NAc pathway.

Bogijetong Decoction and Its Selected Formulation Are Involved in Alleviating Neuropathic Pain in a Rat Model of Chronic Constrictive Injury

Bogijetong decoction (BGJTD) is a formulation that is used for the treatment of neuropathic pain caused by cancer therapy, diabetes, and peripheral nerve injury. In the previous study, we selected four herbal constituents from BGJTD, formulated new decoction (BeD), and demonstrated its efficacy on the neuroprotection of peripheral sciatic nerve in streptozotocin-induced diabetic animals. Here, we report attenuating effects of BGJTD and BeD on neuropathic pain. Neuropathic pain was induced by ligation of the sciatic nerve to generate chronic constrictive injury (CCI). BeD was more effective than BGJTD in alleviating neuropathic pain lasting 3 – 4 weeks after CCI. In vivo administration of BeD did not alter the levels of brain-derived neurotrophic factor (BDNF) which were strongly induced by CCI in the sciatic nerve but downregulated TrkB production in the sciatic nerve. Downregulation of TrkB signals by BeD was confirmed in cultured DRG neurons. BGJTD was more effective in attenuating TNF-α production in the sciatic nerve than BeD, whereas BeD increased IL-6 more efficiently than BGJTD. Furthermore, phopsho-Erk1/2 was increased in the sciatic nerve and dorsal root ganglia (DRG) after BeD treatment. Neurite outgrowth of primary DRG neurons prepared from rats which had undergone CCI for 7 days was significantly increased in BeD-treated group of animals compared to the control and BGJTD-treated groups. Compositional comparison of BeD revealed that the neurite outgrowth was facilitated by the treatments of Panax ginseng and Paeonia lactiflora. Together, these data suggest that BeD induces unique molecular response at the injury site and may trigger retrograde signaling into the neuronal cell body to modulate pain responses.

Intrathecal Injection of Dual Zipper Kinase shRNA Alleviating the Neuropathic Pain in a Chronic Constrictive Nerve Injury Model

Dual leucine zipper kinase (DLK) is a member of mitogen-activated protein kinase kinase kinase (MAP3K) family mainly involved in neuronal degeneration. However, the role of DLK signaling in the neuropathic pain has not yet been fully determined. Chronic constrictive injury (CCI) was conducted by four 3-0 chromic gut ligatures loosely ligated around the sciatic nerve. Escalated DLK expression over the dorsal root ganglion was observed from one to four rings of CCI. Remarkable expression of DLK was observed in primary dorsal root ganglion cells culture subjected to electrical stimulation and attenuated by DLK short hairpin RNA (shRNA) treatment. Intrathecal injection of DLK shRNA attenuates the expression of DLK over the dorsal root ganglion and hippocampus neurons and increased the threshold of mechanical allodynia and decreased thermal hyperalgesia. In CatWalk gait analysis, significant decreases of print area, maximum contact maximum intensity, stand phase, single stance, and regular index by CCI were alleviated by the DLK shRNA administration. In conclusion, the expression of DLK was up-regulated in chronic constrictive injury and attenuated by the administration of DLK shRNA, which paralleled the improvement of neurobehavior of neuropathic pain. The modulation of DLK expression is a potential clinic treatment option for neuropathic pain.

Mambalgins, the Venom-origin Peptides as a Potentially Novel Group of Analgesics: Mini Review

Background: Despite a wide variety of current analgesia regimens, chronic pain is an incredibly difficult condition to treat. Its pathophysiology, initiation, development and course involve a range of different receptors and transmitters. The acid-sensing ion channels (ASICs) are being attributed to an increasingly larger significance in pain aetiology. Over the last few years, the mechanism of ASICs action, influence of their antagonists/agonists and clinical applications have been well described. However, the importance of this protein is significantly larger, not only from the perspective of pain management, but also in psychiatry of addiction or fear. Recently discovered peptides from three-finger toxin group, called mambalgins (isolated from Dendroaspis polylepis polylepsis) exhibit potent analgesic mechanisms of action on ASICs in animal model. Aims & Methods: The article reviews current knowledge in the field of mambalgins and assesses their potential analgesic application, based on the recent experimental evidence. Results: The mambalgins seem to decrease the intensity of the inflammatory, neuropathic and mechanic pain. This has been demonstrated in animal studies of different pain models, including carrageenan- induced inflammatory pain, chronic constrictive injury-induced neuropathic pain and thermal pain. The mechanism of mambalgin action is not clearly defined, but it is suspected that they bind directly to the pH-sensitive region of the ASIC. Conclusion: In this short review, we attempted to summarise the current knowledge about mambalgins and their potential applications as a new substance in searching for the ideal analgesia without common side effects of the other drug groups.