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An action spectrum for melatonin suppression: evidence for a novel non-rod, non-cone photoreceptor system in humans

Thapan, K, Arendt, J and Skene, DJ (2001) An action spectrum for melatonin suppression: evidence for a novel non-rod, non-cone photoreceptor system in humans J PHYSIOL-LONDON, 535 (1). pp. 261-267.

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Abstract

1. Non-image forming, irradiance-dependent responses mediated by the human eye include synchronisation of the circadian axis and suppression of pineal melatonin production. The retinal photopigment(s) transducing these light responses in humans have not been characterised. 2. Using the ability of light to suppress nocturnal melatonin production, we aimed to investigate its spectral sensitivity and produce an action spectrum. Melatonin suppression was quantified in 22 volunteers in 215 light exposure trials using monochromatic light (30 min pulse administered at circadian time (CT) 16–18) of different wavelengths (gmax 424, 456, 472, 496, 520 and 548 nm) and irradiances (0.7–65.0 μW cm_2). 3. At each wavelength, suppression of plasma melatonin increased with increasing irradiance. Irradiance–response curves (IRCs) were fitted and the generated half-maximal responses (IR50) were corrected for lens filtering and used to construct an action spectrum. 4. The resulting action spectrum showed unique short-wavelength sensitivity very different from the classical scotopic and photopic visual systems. The lack of fit (r2 < 0.1) of our action spectrum with the published rod and cone absorption spectra precluded these photoreceptors from having a major role. Cryptochromes 1 and 2 also had a poor fit to the data. Fitting a series of Dartnall nomograms generated for rhodopsin-based photopigments over the gmax range 420–480 nm showed that rhodopsin templates between gmax 457 and 462 nm fitted the data well (r2 ≥ 0.73). Of these, the best fit was to the rhodopsin template with gmax 459 nm (r2 = 0.74). 5. Our data strongly support a primary role for a novel short-wavelength photopigment in lightinduced melatonin suppression and provide the first direct evidence of a non-rod, non-cone photoreceptive system in humans.

Item Type: Article
Authors :
AuthorsEmailORCID
Thapan, KUNSPECIFIEDUNSPECIFIED
Arendt, JUNSPECIFIEDUNSPECIFIED
Skene, DJUNSPECIFIEDUNSPECIFIED
Date : 15 August 2001
Uncontrolled Keywords : NOCTURNAL PLASMA MELATONIN, HUMAN CIRCADIAN PACEMAKER, BRIGHT LIGHT, RETINOHYPOTHALAMIC TRACT, OCULAR PHOTORECEPTORS, RHYTHMS, PINEAL, SENSITIVITY, WAVELENGTH, ALERTNESS
Depositing User : Symplectic Elements
Date Deposited : 28 Mar 2017 14:39
Last Modified : 28 Mar 2017 14:39
URI: http://epubs.surrey.ac.uk/id/eprint/207050

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