The melanin-concentrating hormone (MCH) is a peptidergic neuromodulator synthesized by neurons in the lateral hypothalamus and zona incerta. MCHergic neurons project throughout the central nervous system, indicating the involvements of many physiological functions, but the role in pain has yet to be determined. In this study, we found that pMCH−/− mice showed lower baseline pain thresholds to mechanical and thermal stimuli than did pMCH+/+ mice, and the time to reach the maximum hyperalgesic response was also significantly earlier in both inflammatory and neuropathic pain. To examine its pharmacological properties, MCH was administered intranasally into mice, and results indicated that MCH treatment significantly increased mechanical and thermal pain thresholds in both pain models. Antagonist challenges with naltrexone (opioid receptor antagonist) and AM251 (cannabinoid 1 receptor antagonist) reversed the analgesic effects of MCH in both pain models, suggesting the involvement of opioid and cannabinoid systems. MCH treatment also increased the expression and activation of CB1R in the medial prefrontal cortex and dorsolateral- and ventrolateral periaqueductal grey. The MCH1R antagonist abolished the effects induced by MCH. This is the first study to suggest novel analgesic actions of MCH, which holds great promise for the application of MCH in the therapy of pain-related diseases.

Over the past several decades, clinical studies have shown significant analgesic effects of acupuncture. The efficacy of acupuncture treatment has improved with the recent development of nanoporous needles (PN), which are produced by modifying the needle surface using nanotechnology. Herein, we showed that PN at acupoint ST36 produces prolonged analgesic effects in an inflammatory pain model; the analgesic effects of PN acupuncture were sustained over 2 h, while those using a conventional needle (CN) lasted only 30 min. In addition, the PN showed greater therapeutic effects than CN after 10 acupuncture treatments once per day for 10 days. We explored how the porous surface of the PN contributes to changes in local tissue, which may in turn result in enhanced analgesic effects. We showed that the PN has greater rotational torque and pulling force than the CN, particularly at acupoints ST36 and LI11, situated on thick muscle layers. Additionally, in ex vivo experiments, the PN showed greater winding of subcutaneous connective tissues and muscle layers. Our results suggest that local mechanical forces are augmented by the PN and its nanoporous surface, contributing to the enhanced and prolonged analgesic effects of PN acupuncture.

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Objectives : Mast cells, the multifunctional immune cells which can be activated by various stimulations, have been in the limelight recently at the fields of acupuncture research. This study aimed to investigate the association between the distribution of mast cell and acupoint specificity. We focused on the characteristics of mast cell distribution of acupoints in normal, pathologically sensitized, and acupoint-stimulated state. Methods : Literature searches were performed on PubMed and EMBASE for dates ranging to February 2019, by using terms "acupuncture", "moxibustion", "acupoint", "mast cell". Finally, 18 papers were collected by inclusion and exclusion criteria. To assess the quality of included studies, modified SYRCLE's risk of bias tool for animal studies was used. Results : Overall, the studies showed that the number of the mast cells was higher in acupoints than non-acupoints. After pathological sensitization, increasing tendency towards the mast cell number was reported in acupoints. The increase of mast cells was also observed after acupuncture or moxibustion. However, when the acupoint stimulation was repeated for several days in pathological models, the results did not show consistent tendency. In quality assessments, most of the studies showed unclear risk of bias. Conclusions : The studies showed a consistent trend about the association with mast cell distribution and acupoint specificity. However, we could not certainly affirm the relationship due to insufficient qualities of included studies. Not only the distribution but also the functions should be considered in further researches to identify the relationship between mast cells and acupuncture effect.