Consistent interindividual increases or decreases in muscle sympathetic nerve activity during experimental muscle pain

• Published in: Experimental brain research Vol. 232; no. 4; pp. 1309 - 1315
• Main Authors: Fazalbhoy, Azharuddin, Birznieks, Ingvars, Macefield, Vaughan G.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.04.2014; Springer; Springer Nature B.V
• Subjects: Adolescent; Adrenergic Fibers - drug effects; Adrenergic Fibers - physiology; Adult; Analysis; Biological and medical sciences; Biomedical and Life Sciences; Biomedicine; Blood pressure; Blood Pressure - drug effects; Blood Pressure - physiology; Chronic fatigue syndrome; Female; Fundamental and applied biological sciences. Psychology; Heart rate; Heart Rate - drug effects; Heart Rate - physiology; Human subjects; Humans; Hypotheses; Male; Muscle pain; Muscle, Skeletal - drug effects; Muscle, Skeletal - physiology; Myalgia; Myalgia - chemically induced; Myalgia - diagnosis; Myalgia - physiopathology; Nervous system; Nervous system, Sympathetic; Neurology; Neurosciences; Physiological aspects; Physiology; Recording sessions; Research Article; Saline Solution, Hypertonic - toxicity; Somesthesis and somesthetic pathways (proprioception, exteroception, nociception); interoception; electrolocation. Sensory receptors; Sympathetic Nervous System - drug effects; Sympathetic Nervous System - physiology; Vertebrates: nervous system and sense organs; Young Adult; Sydney New South Wales Australia; Australia; Muscle sympathetic nerve activity; Pain; Chronic pain; Nociceptive pain; Sympathetic nerve; Nociception; Chronic; Muscle
• ISSN: 0014-4819; 1432-1106
• DOI: 10.1007/s00221-014-3847-7

We recently showed that long-lasting muscle pain, induced by intramuscular infusion of hypertonic saline, evoked two patterns of cardiovascular responses across subjects: one group showed parallel increases in muscle sympathetic nerve activity (MSNA), blood pressure, and heart rate, while the other group showed parallel decreases. Given that MSNA is consistent day to day, we tested the hypothesis that individuals who show increases in MSNA during experimental muscle pain will show consistent responses over time. MSNA was recorded from the peroneal nerve, together with blood pressure and heart rate, during an intramuscular infusion of hypertonic saline causing pain for an hour in 15 subjects on two occasions, 2–27 weeks apart. Pain intensity ratings were not significantly different between the first (5.8 ± 0.4/10) and second (6.1 ± 0.2) recording sessions. While four subjects showed significant decreases in the first session (46.6 ± 9.2 % of baseline) and significant increases in the second (159.6 ± 8.9 %), in 11 subjects, there was consistency in the changes in MSNA over time: either a sustained decrease (55.6 ± 6.8 %, n  = 6) or a sustained increase (143.5 ± 6.1 %, n  = 5) occurred in both recording sessions. There were no differences in pain ratings between sessions for any subjects. We conclude that the changes in MSNA during long-lasting muscle pain are consistent over time in the majority of individuals, reflecting the importance of studying interindividual differences in physiology.