Interstitial concentration of serotonin is increased in myalgic human trapezius muscle during rest, repetitive work and mental stress - an in vivo microdialysis study

• OBJECTIVES: The pathophysiology of trapezius myalgia is not fully elucidated. Serotonin (5-HT) is involved in modulation of nociception and hyperalgesia. Our aim was to compare the interstitial 5-HT levels of the trapezius muscle in women with chronic trapezius myalgia and in pain-free controls. MATERIALS AND METHODS: Microdialysate of the trapezius muscle collected every 20 minutes during rest, work (100 min) and stress (20 min) was used to study the dynamics of 5-HT in women with chronic trapezius myalgia (MYA; n=18) and in pain-free controls (CON; n=30). RESULTS: MYA had higher levels of 5-HT than CON at baseline, during repetitive work, during mental stress and during recovery. There were no significant time effects on 5-HT levels. CONCLUSION: 5-HT has the potential of a biomarker of chronic myalgia. Elevated levels of 5-HT may be involved in maintenance of habitual chronic pain and might contribute to increased pain during exercise by facilitating the effect of released algesic substances linked to such muscle demands.

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