Melatonin attenuates the vestibulosympathetic but not vestibulocollic reflexes in humans: selective impairment of the utricles.
Study Goal
The researchers aimed to determine if melatonin alters the vestibulosympathetic reflex (VSR) and vestibulocollic reflex (VCR) in humans.
Results Summary
Melatonin significantly attenuated MSNA responses during head-down rotation (HDR) compared to placebo, indicating an effect on the VSR, but did not alter the timing or amplitude of vestibular evoked myogenic potentials (VEMP), suggesting no effect on the VCR.
Population
12 healthy subjects (28 ± 1 yr; 6 men, 6 women) for study 1; 10 healthy subjects (26 ± 1 yr; 4 men, 6 women) for study 2.
Effective Dosage
3 mg melatonin (single dose).
Duration
Acute (45 minutes post-ingestion for study 1; timing not specified for study 2).
Interactions
None mentioned
| Intervention | Direction | Endpoint | Population | Dosage | Impact | Claim # |
|---|---|---|---|---|---|---|
melatonin | decrease | nerve activity of medial vestibular nuclei | the rat | - | has been reported to decrease | #1 |
melatonin | decrease | muscle sympathetic nerve activity (MSNA) responses to baroreceptor unloading | humans | - | is associated with attenuated | #2 |
melatonin (3 mg) | decrease | MSNA responses during HDR | 12 healthy subjects (28 ± 1 yr; 6 men, 6 women) | burst frequency Δ 4 ± 1 vs. Δ 7 ± 1 bursts/min, and total MSNA Δ 51 ± 20 and Δ 96 ± 15%, respectively | significantly attenuated | #3 |
melatonin (3 mg) | no change | the timing of the p13 and n23 peaks | 10 healthy subjects (26 ± 1 yr; 4 men and 6 women) | pre-melatonin 13.2 ± 0.4 and 21.3 ± 0.6 ms vs. post-melatonin 13.5 ± 0.4 and 21.4 ± 0.7 ms, respectively | did not alter | #4 |
melatonin (3 mg) | no change | the p13-n23 interpeak amplitudes | 10 healthy subjects (26 ± 1 yr; 4 men and 6 women) | pre-melatonin 22.5 ± 4.6 arbitrary units (au) and post-melatonin 22.7 ± 4.6 au | did not alter | #5 |
melatonin | decrease | the VSR | - | - | attenuates | #6 |
melatonin | decrease | orthostatic tolerance | - | - | negatively affects | #7 |
melatonin | no change | the VCR | humans | - | does not alter | #8 |
Melatonin has been reported to decrease nerve activity of medial vestibular nuclei in the rat and is associated with attenuated muscle sympathetic nerve activity (MSNA) responses to baroreceptor unloading in humans. The purpose of this study was to determine if melatonin alters the vestibulosympathetic reflex (VSR) and vestibulocollic reflex (VCR) in humans. In study 1, MSNA, arterial blood pressure, and heart rate were measured in 12 healthy subjects (28 ± 1 yr; 6 men, 6 women) during head-down rotation (HDR) before and 45 min after ingestion of either melatonin (3 mg) or placebo (sucrose). Subjects returned at least 2 days later at the same time of day to repeat the trial after ingesting the opposite treatment (melatonin or placebo). Melatonin significantly attenuated MSNA responses during HDR compared with placebo (burst frequency Δ 4 ± 1 vs. Δ 7 ± 1 bursts/min, and total MSNA Δ 51 ± 20 and Δ 96 ± 15%, respectively; P < 0.02). In study 2, vestibular evoked myogenic potentials (VEMP) were measured in 10 healthy subjects (26 ± 1 yr; 4 men and 6 women) before and after ingestion of 3 mg melatonin. Melatonin did not alter the timing of the p13 and n23 peaks (pre-melatonin 13.2 ± 0.4 and 21.3 ± 0.6 ms vs. post-melatonin 13.5 ± 0.4 and 21.4 ± 0.7 ms, respectively) or the p13-n23 interpeak amplitudes [pre-melatonin 22.5 ± 4.6 arbitrary units (au) and post-melatonin 22.7 ± 4.6 au]. In summary, melatonin attenuates the VSR and supports the concept that melatonin negatively affects orthostatic tolerance. However, melatonin does not alter the VCR in humans suggesting melatonin's effect on the VSR appears to be mediated by the utricles.