Background & Aims
Interactions between pain and the sympathetic nervous system (SNS) are complicated and vary depending on many stimulus-related factors. Acute pain can induce a stress response, and acute stress suppresses pain (i.e., stress-induced analgesia). Sympathetic activation, specifically muscle sympathetic nerve activity (MSNA), can be measured via microneurographic targeting and recording of sympathetic efferent nerve impulses. MSNA is believed to increase when a participant is exposed to an acute painful stimulus. However, while the effects of acute pain on MSNA have been sufficiently investigated, what is less understood is the response of MSNA to long-lasting pain, the far more important clinical entity, as chronic SNS activation is linked to the development and maintenance of chronic pain. Therefore, the primary aim of this study was to examine the relationship between MSNA and pain during an extended 6-min cold pressor test (CPT), a potent pain and sympathetic stimulus. We hypothesized that changes in MSNA would be positively correlated with changes in pain ratings, and that both would increase steadily and concomitantly throughout a 6-min CPT.
Methods
We obtained integrated MSNA—quantified as burst frequency (bursts/minute)—using peroneal microneurography (NeuroAmp, ADI) during 10-min of supine, baseline rest (BSL) and CPT (~4 °C) in 18 young, healthy individuals (9 men, 9 women; ages 18-35). Participants reported pain on a numerical rating scale (0–10) during BSL and CPT (timepoints: 30 s, 120 s, 240 s, and 330 s).
Results
Both pain (p<0.001) and total MSNA (p<0.001) increased in the initial 30-sec of the CPT and did not significantly change thereafter. Only females showed initial increases in burst frequency (p<0.001) and burst incidence (p=0.049). A linear regression analysis of the relationship between pain and burst frequency (PainxBF) demonstrated that both males (r=0.54, p=0.13) and females (r=0.43, p=0.17) display a moderate positive relationship during the first 30-sec of the CPT, but this relationship gradually weakens over time. Females showed a consistent moderate positive relationship between area-under-the-curve (AUC) values of PainxBF (r=0.39, p=0.20) and PainxTotalMSNA (r=0.42, p=0.17) over the first 4-mininutes of the CPT, while males showed a significant positive linear relationship between PainxHeartRate (p=0.001) during this time.
Conclusions
In summary, pain and MSNA covary acutely, yet do not covary over a tonic timespan. This tonic variation differs between sexes and therefore may be influenced by different endogenous mechanisms. These findings imply that prolonged pain stimuli may activate descending pain modulation mechanisms, altering the relationship between MSNA and long-lasting pain in a manner that needs further investigation.
References
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Presenting Author
Laila A Chaudhry
Poster Authors
Laila Chaudhry
BSc
Alan Edwards Centre for Research on Pain, McGill University, Montreal, Quebec, Canada
Lead Author
Yasmine Coovadia
MSc
Cardiovascular Health and Autonomic Regulation Lab, Department of Kinesiology & Physical Education, McGill University, Montreal, Quebec, Canada
Lead Author
Brittany K Schwende
MSc
Cardiovascular Health and Autonomic Regulation Lab, Department of Kinesiology & Physical Education, McGill University, Montreal, Quebec, Canada
Lead Author
Danielle E Berbrier
MSc
Cardiovascular Health and Autonomic Regulation Lab, Department of Kinesiology & Physical Education, McGill University, Montreal, Quebec, Canada
Lead Author
Will Huckins
BSc
Cardiovascular Health and Autonomic Regulation Lab, Department of Kinesiology & Physical Education, McGill University, Montreal, Quebec, Canada
Lead Author
Jinan Saboune
MSc
Cardiovascular Health and Autonomic Regulation Lab, Department of Kinesiology & Physical Education, McGill University, Montreal, Quebec, Canada
Lead Author
Derek A Skolnik
BSc
Cardiovascular Health and Autonomic Regulation Lab, Department of Kinesiology & Physical Education, McGill University, Montreal, Quebec, Canada
Lead Author
Emily K VanBerkel
BSc
Cardiovascular Health and Autonomic Regulation Lab, Department of Kinesiology & Physical Education, McGill University, Montreal, Quebec, Canada
Lead Author
Jeffrey Mogil
Alan Edwards Centre for Research on Pain, McGill University, Montreal, Quebec, Canada
Lead Author
Charlotte W Usselman
PhD
Cardiovascular Health and Autonomic Regulation Lab, Department of Kinesiology & Physical Education, McGill University, Montreal, Quebec, Canada
Lead Author
Topics
- Gender/Sex Differences