Elsevier

Neuroscience Letters

Volume 232, Issue 1, 22 August 1997, Pages 57-61
Neuroscience Letters

The hypothermic effect of late evening melatonin does not block the phase delay induced by concurrent bright light in human subjects

https://doi.org/10.1016/S0304-3940(97)00553-3Get rights and content

Abstract

This constant routine study (n=9 men) compared the phase delay of the circadian system induced by a single pulse of evening light (5000 lx at 2100–2400 h) in the presence or absence of exogenous melatonin (5 mg p.o. at 2040 h). On the treatment day, light and melatonin protracted and accelerated, respectively, the evening decline in core body temperature (CBT). Subjective sleepiness ratings showed parallel shifts, the earlier the decline in CBT, the sleepier. On the post-treatment day, light induced a phase delay in the mid-range crossing time of CBT decline independent of whether melatonin was co-administered or not. Subjective sleepiness was delayed in parallel. The phase delay of the circadian system by evening light appears to be independent of an immediate hyperthermic effect and is not mediated by melatonin.

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Acknowledgements

This study was supported by SNF #32-4245.94 and the Sandoz Foundation. K.V.D. was a IBRO Switzerland Fellow. We thank C. Renz, M.-F. Dattler, G. Balestrieri and M. von Arb for their assistance in data acquisition.

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