Background & Aims
Muscle sensations triggered by acidosis are often labeled as pain and are typically transmitted by nociceptors. However, it’s noteworthy that up to 80% of non-nociceptive muscle afferents are sensitive to acidity, suggesting a potential role in non-pain sensations associated with acidosis. Sng, a prevalent non-pain complaint, is commonly reported among Chinese speakers. In our previous study, we demonstrated a spinal cord injury patient who lost pain sensation on his injured leg but with intact proprioceptive function. Interestingly, he can still feel sng. Despite the impaired spinothalamic tract function, the intact proprioceptive tract may allow the patient to experience sng. Nevertheless, the influence of acidosis-induced proprioceptive signals on brain activity remains largely unexplored. The aims of this study were to ascertain whether an acidic solution triggers a sng response and to explore the influence of acidosis-evoked proprioceptive signals on brain connectivity using fMRI.
Methods
This is a prospective single-blinded study. Thirty-eight healthy subjects (18 males and 20 females) participated in a single visit, which included an 8-minute baseline fMRI scan, an 8-minute infusion fMRI scan with simultaneous intramuscular infusion of pH 5.2 acidic sodium phosphate solution into the left tibialis muscle at a rate of 40 ml/hr, and a 15-minute post-infusion fMRI scan. Sng and pain visual analogue scales (VAS) were assessed before, during and after the fMRI trial. Functional connectivity (FC) related to proprioception (S1_3a and S1_3b) were analyzed at different stages of the fMRI process.
Results
The acidic solution induced a strong sng VAS in the muscles and a mild muscle pain VAS (immediately after acidic PBS infusion: 5.34 ± 2.40 and 2.53 ± 2.19; 4-minute post-infusion: 2.71 ± 2.24 and 0.97 ± 1.39, respectively) — this effect was not dependent on gender. In cases of significant sng response (sng VAS immediately after acidic PBS infusion ? 3, pain VAS < 3, n=16), when regions of interest (ROIs) were chosen at S1_3a and S1_3b, the significant higher functional connectivity was observed at the ACC, paracingulate gyrus, frontal pole, superior frontal gyrus, angular gyrus and lateral occipital cortex during the infusion. The S1_3b – precentral gyrus and S1_3a – superior frontal gyrus demonstrated the significant differences at the first and third 4-minute time points of post-infusion stage, respectively.
Conclusions
The preliminary results indicate that muscle acidosis can give rise to non-pain sensation, specifically the sensation of sng. S1_3a and S1_3b are identified as potential key proprioceptive signals triggered by acidosis which may contribute to the perception of sng in the brain.
References
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Presenting Author
Chen-Ling Lan
Poster Authors
Chen-Ling Lan
Taipei Medical University Hospital
Lead Author
Yu-Chun Lo
Taipei Medical University Hospital
Lead Author
Ting-Chun Lin
Taipei Medical University Hospital
Lead Author
Yu-Wen Yu
Taipei Medical University Hospital
Lead Author
Li-Chun Hsieh
Taipei Medical University Hospital
Lead Author
Chih-Cheng Chen
Taipei Medical University Hospital
Lead Author
Jiann-Her Lin
MD, PhD
Taipei Medical University Hospital
Lead Author
Topics
- Pain Imaging