Glucocorticoid Receptor Contributes to Electroacupuncture-Induced Analgesia by Inhibiting Nav1.7 Expression in Rats With Inflammatory Pain Induced by Complete Freund's Adjuvant

A systematic review of the pain-related emotional and cognitive impairments in chronic inflammatory pain induced by CFA injection and its mechanism

Emotional and cognitive impairments are comorbidities commonly associated with chronic inflammatory pain. To summarize the rules and mechanisms of comorbidities in a complete Freund's adjuvant (CFA)-induced pain model, we conducted a systematic review of 66 experimental studies identified in a search of three databases (PubMed, Web of Science, and ScienceDirect). Anxiety-like behaviors developed at 1- or 3-days post-CFA induction but also appeared between 2- and 4 weeks post-induction. Pain aversion, pain depression, and cognitive impairments were primarily observed within 2 weeks, 4 weeks, and 2-4 weeks post-CFA injection, respectively. The potential mechanisms underlying the comorbidities between pain and anxiety predominantly involved heightened neuronal excitability, enhanced excitatory synaptic transmission, and neuroinflammation of anterior cingulate cortex (ACC) and amygdala. The primary somatosensory cortex (S1)Glu→caudal dorsolateral striatum (cDLS)GABA, medial septum (MS)CHAT→rACC, rACCGlu→thalamus, parabrachial nucleus (PBN)→central nucleus amygdala (CeA), mediodorsal thalamus (MD)→basolateral amygdala (BLA), insular cortex (IC)→BLA and anteromedial thalamus nucleus (AM)CaMKⅡ→midcingulate cortex (MCC)CaMKⅡ pathways are enhanced in the pain-anxiety comorbidity. The ventral hippocampal CA1 (vCA1)→BLA and BLA→CeA pathways were decreased in the pain-anxiety comorbidity. The BLA→ACC pathway was enhanced in the pain-depression comorbidity. The infralimbic cortex (IL)→locus coeruleus (LC) pathway was enhanced whereas the vCA1→IL pathway was decreased, in the pain-cognition comorbidity. Inflammation/neuroinflammation, oxidative stress, apoptosis, ferroptosis, gut-brain axis dysfunction, and gut microbiota dysbiosis also contribute to these comorbidities.

Glucose attenuates the long-term adverse neurodevelopment effect of neonate pain stimulus via CRF/GR in rats

BACKGROUND

Neonates undergo numerous painful procedures throughout their hospitalization. Repeated procedural pain may cause adverse long-term effects. Glucose as a non-pharmacological analgesia, is used for neonate pain management. In this study, potential mechanism of attenuate pain induced by glucose in neurodevelopment effect of neonate pain stimulus was investigated.

METHODS

Neonatal rats to perform a repetitive injury model and glucose intervention model in the postnatal day 0-7(P0-7). Pain thresholds were measured by von Frey test weekly. The puberty behavioral outcome, tissue loss and protein expression in hippocampus were analyzed.

RESULTS

Oral administration of glucose after repeated pain stimulation can maintain the hippocampal structure in, and reduce the expressions of corticotropin releasing factor (CFR) and glucocorticoid receptor (GR), therefore, resulted in long-term threshold of pain and cognitive improvement.

CONCLUSION

Exposure to neonatal repeated procedural pain causes persistent mechanical hypersensitivity and the dysfunction of spatial memory retention at puberty. In addition, glucose can relieve these adverse effects, possibly via decreasing CRF/GR levels to change the hypothalamus-pituitary-adrenal (HPA) axis.

Role of SIRT5 in the analgesic effectiveness of moxibustion at ST36 in mice with inflammatory pain

Sirtuine5 (SIRT5) is an important molecule involved in the pathology of inflammatory diseases. To investigate the impact of SIRT5 on the analgesic effectiveness of moxibustion, we established a complete Freund's adjuvant- (CFA-) induced inflammatory pain in mice model. Moxibustion was applied at the Zusanli (ST36) acupoint in mice with inflammatory pain. The analgesic effectiveness was evaluated by thermal hyperalgesia and mechanical allodynia tests in the right paws after CFA injection. The expression of inflammatory cytokines, including the pro-inflammatory factors IL-1β and TNF-α, and the anti-inflammatory factors IL-4 and TGF-β expressions, was evaluated using by ELISA. Furthermore, SIRT5 was evaluated by immunofluorescence and western blotting. The results showed that, compared with the CFA group, both thermal and mechanical pain thresholds increased with moxibustion and the SIRT5 inhibitor MC3482 intervention at ST36. Additionally, compared to the CFA-induced group, the inflammatory mediators, including IL-1β and TNF-α, decreased, while the anti-inflammatory cytokines IL-4 and TGF-β increased with moxibustion and MC3482 ST36 acupoint injection. Western blot results showed a decreased expression of SIRT5 at the ST36 site with moxibustion and MC3482 injection, compared to the CFA-induced group. SIRT5 expression in the right paw of mice injected with moxibustion and MC3482 was higher than that in the CFA-induced group. This study revealed that SIRT5 expression is involved in moxibustion analgesia and may be a potential mediator in the regulation of analgesia.

Combined-Acupoint Electroacupuncture Induces Better Analgesia via Activating the Endocannabinoid System in the Spinal Cord

Electroacupuncture (EA) therapy has been widely reported to alleviate neuropathic pain with few side effects in both clinical practice and animal studies worldwide. However, little is known about the comparison of the therapeutic efficacy among the diverse EA schemes used for neuropathic pain. The present study is aimed at investigating the therapeutic efficacy discrepancy between the single and combined-acupoint EA and to reveal the difference of mechanisms behind them. Electroacupuncture was given at both Zusanli (ST36) and Huantiao (GB30) in the combined group or ST36 alone in the single group. Paw withdrawal mechanical threshold (PWMT) was measured to determine the pain level. Electrophysiology was performed to detect the effects of EA on synaptic transmission in the spinal dorsal horn of the vGlut2-tdTomato mice. Spinal contents of endogenous opioids, endocannabinoids, and their receptors were examined. Inhibitors of CBR (cannabinoid receptor) and opioid receptors were used to study the roles of opioid and endocannabinoid system (ECS) in EA analgesia. We found that combined-acupoint acupuncture provide stronger analgesia than the single group did, and the former inhibited the synaptic transmission at the spinal level to a greater extent than later. Besides, the high-intensity stimulation at ST36 or normal stimulation at two sham acupoints did not mimic the similar efficacy of analgesia in the combined group. Acupuncture stimulation in single and combined groups both activated the endogenous opioid system. The ECS was only activated in the combined group. Naloxone totally blocked the analgesic effect of single-acupoint EA; however, it did not attenuate that of combined-acupoint EA unless coadministered with CBR antagonists. Hence, in the CCI-induced neuropathic pain model, combined-acupoint EA at ST36 and GB30 is more effective in analgesia than the single-acupoint EA at ST36. EA stimulation at GB30 alone neither provided a superior analgesic effect to EA treatment at ST36 nor altered the content of AEA, 2-AG, CB1 receptor, or CB2 receptor compared with the CCI group. Activation of the ECS is the main contributor of the better analgesia by the combined acupoint stimulation than that induced by single acupoint stimulation.

Spinal Sirtuin 3 Contributes to Electroacupuncture Analgesia in Mice with Chronic Constriction Injury–Induced Neuropathic Pain

BACKGROUND

Electroacupuncture (EA) is a traditional Chinese therapeutic technique that has a beneficial effect on neuropathic pain; however, the specific mechanism remains unclear. In this study, we investigated whether EA inhibits spinal Ca/calmodulin-dependent protein kinase II (CaMKIIα) phosphorylation through Sirtuin 3 (SIRT3) protein, thus relieving neuropathic pain.

MATERIALS AND METHODS

We used wild-type and SIRT3 knockout (SIRT3^-/-) mice and used chronic constriction injury (CCI) as a pain model. We performed Western blotting, immunostaining, von Frey, and Hargreaves tests to gather biochemical and behavioral data. Downregulation and overexpression and spinal SIRT3 protein were achieved by intraspinal injection of SIRT3 small interfering RNA and intraspinal injection of lentivirus-SIRT3. To test the hypothesis that CaMKIIα signaling was involved in the analgesic effects of EA, we expressed CaMKIIα-specific designer receptors exclusively activated by designer drugs (DREADDs) in the spinal dorsal horn (SDH) of mice.

RESULTS

These results showed that the mechanical and thermal hyperalgesia induced by CCI was related to the decreased spinal SIRT3 expression in the SDH of mice. A significant reduction of mechanical and thermal thresholds was found in the SIRT3^-/- mice. SIRT3 overexpression or EA treatment alleviated CCI-induced neuropathic pain and prevented the spinal CaMKIIα phosphorylation. Most importantly, EA increased the expression of spinal SIRT3 protein in the SDH. Downregulation of spinal SIRT3 or CaMKIIα Gq-DREADD activation inhibited the regulatory effect of EA on neuropathic pain.

CONCLUSION

Our results showed that CaMKIIα phosphorylation was inhibited by spinal SIRT3 in neuropathic pain and that EA attenuated CCI-induced neuropathic pain mainly by upregulating spinal SIRT3 expression in the SDH of mice.