The impact of baroreflex function on endogenous pain control: a microneurography study

The interaction between sympathetic vasoconstrictor activity to muscles [muscle sympathetic nerve activity (MSNA), burst frequency (BF) and burst incidence (BI)] and different stress and somatosensory stimuli is still unclear. Eighteen healthy men (median age 28 years) underwent microneurography recordings from the peroneal nerve. MSNA was recorded during heat pain (HP) and cold pain (CP) alone as well as combined with different stress tasks (mental arithmetic, singing, giving a speech). An additional nine healthy men (median age 26 years) underwent the stimulation protocol with an additional control task (thermal pain combined with listening to music) to evaluate possible attentional confounders. MSNA was significantly increased by CP and HP. CP‐evoked responses were smaller. The diastolic blood pressure followed the time course of MSNA while heart rate remained unchanged. The mental stress tasks further increased MSNA and were sufficient to reduce pain while the control task had no effect. MSNA activity correlated negatively with pain intensity and positively with analgesia. High blood pressure values were associated with lower pain intensity. Our study indicates an impact of central sympathetic drive on pain and pain control. Using microneurography we found thermal pain to increase MSNA. Different mental stress tasks further increased MSNA independent from perceived stress. In contrast to the control task, the mental stress tasks were sufficient to reduce thermal pain indicating stress‐induced analgesia. High MSNA vasoconstrictor outflow was associated with decreased thermal pain intensity and high stress‐induced pain reduction. Our study directly indicates an impact of central sympathetic drive on pain and pain control.