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Circadian variations of human flexion reflex
Giorgio Sandrini1, Enrico Alfonsi, Giorgio Bono
1Headache Centre, Neurological Department, "C. Mondino" Foundation, University of Pavia, 27100 Pavia, Italy Department of Obstetrics and Gynecology, University of Modena, ModenaItaly.
Pain
|June 1, 1986
Summary
Human nociceptive flexion reflexes show daily circadian rhythms, with pain sensitivity lowest in the early morning and highest at midnight. Beta-endorphin levels did not correlate with these reflex changes.
Area of Science:
- Neuroscience
- Chronobiology
- Human Physiology
Background:
- The human body exhibits daily biological rhythms, known as circadian rhythms, influencing various physiological processes.
- Nociception, the sensory nervous system's process of encoding noxious stimuli, is a complex pathway potentially modulated by circadian factors.
Purpose of the Study:
- To investigate the presence and characteristics of circadian rhythmicity in nociceptive flexion reflex thresholds in healthy human subjects.
- To explore potential correlations between circadian variations in nociceptive reflexes and plasma beta-endorphin levels.
Main Methods:
- Eight healthy male volunteers participated in the study.
- Reflex II (RII) and Reflex III (RIII) thresholds were measured every 6 hours over a 24-hour period.
- Mean cosinor analysis was employed to identify significant rhythms, and plasma beta-endorphin levels were assessed in a subset of participants.
Main Results:
- Both RII and RIII thresholds demonstrated significant circadian rhythmicity.
- Lowest reflex thresholds were observed in the early morning, while the highest were recorded around midnight.
- Mean cosinor analysis confirmed significant rhythms with acrophases at 20:12 for RII and 22:29 for RIII.
- No correlation was found between circadian changes in beta-endorphin levels and the RIII threshold.
Conclusions:
- Human nociceptive flexion reflexes exhibit a clear circadian rhythm, indicating daily fluctuations in pain sensitivity.
- Circadian variations in nociceptive reflexes are not directly correlated with plasma beta-endorphin levels, suggesting other regulatory factors are involved.