• Kenta Wakaizumi, Takashige Kondo, Yusuke Hamada, Michiko Narita, Rui Kawabe, Hiroki Narita, Moe Watanabe, Shigeki Kato, Emiko Senba, Kazuto Kobayashi, Naoko Kuzumaki, Akihiro Yamanaka, Hiroshi Morisaki, and Minoru Narita.
• Department of Anesthesiology, Keio University of Medicine, Tokyo, Japan.
• Mol Pain. 2016 Jan 1; 12.

BackgroundExercise alleviates pain and it is a central component of treatment strategy for chronic pain in clinical setting. However, little is known about mechanism of this exercise-induced hypoalgesia. The mesolimbic dopaminergic network plays a role in positive emotions to rewards including motivation and pleasure. Pain negatively modulates these emotions, but appropriate exercise is considered to activate the dopaminergic network. We investigated possible involvement of this network as a mechanism of exercise-induced hypoalgesia.MethodsIn the present study, we developed a protocol of treadmill exercise, which was able to recover pain threshold under partial sciatic nerve ligation in mice, and investigated involvement of the dopaminergic reward network in exercise-induced hypoalgesia. To temporally suppress a neural activation during exercise, a genetically modified inhibitory G-protein-coupled receptor, hM4Di, was specifically expressed on dopaminergic pathway from the ventral tegmental area to the nucleus accumbens.ResultsThe chemogenetic-specific neural suppression by Gi-DREADD system dramatically offset the effect of exercise-induced hypoalgesia in transgenic mice with hM4Di expressed on the ventral tegmental area dopamine neurons. Additionally, anti-exercise-induced hypoalgesia effect was significantly observed under the suppression of neurons projecting out of the ventral tegmental area to the nucleus accumbens as well.ConclusionOur findings suggest that the dopaminergic pathway from the ventral tegmental area to the nucleus accumbens is involved in the anti-nociception under low-intensity exercise under a neuropathic pain-like state.© The Author(s) 2016.

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