Journal Article

Melanopsin Bistability: A Fly's Eye Technology in the Human Retina

Institut National de la Santé et de la Recherche Médicale (INSERM), Department of Ophtalmology ; Hôpital Edouard Herriot [CHU - HCL] ; Hospices Civils de Lyon (HCL)-Hospices Civils de Lyon (HCL), Mure, Ludovic, INSERM U846, département de chronobiologie, Cornut, Pierre-Loic, Denis, Philippe, Centre de recherche en neurosciences de Lyon - Lyon Neuroscience Research Center (CRNL) ; Université Claude Bernard Lyon 1 (UCBL) ; Université de Lyon-Université de Lyon-Université Jean Monnet - Saint-Étienne (UJM)-Institut National de la Santé et de la Recherche Médicale (INSERM)-Centre National de la Recherche Scientifique (CNRS), Rieux, Camille, Gronfier, Claude, Drouyer, Elise, Institut cellule souche et cerveau (SBRI) ; Institut National de la Recherche Agronomique (INRA)-Université Claude Bernard Lyon 1 (UCBL) ; Université de Lyon-Université de Lyon-Institut National de la Santé et de la Recherche Médicale (INSERM), Université Claude Bernard Lyon 1 (UCBL) ; Université de Lyon, Centre Hospitalier Universitaire de Lyo

2009

Overview

In addition to rods and cones, the human retina contains light-sensitive ganglion cells that express melanopsin, a photopigment with signal transduction mechanisms similar to that of invertebrate rhabdomeric photopigments (IRP). Like fly rhodopsins, melanopsin acts as a dual-state photosensitive flip-flop in which light drives both phototransduction responses and chromophore photoregeneration that bestows independence from the retinoid cycle required by rods and cones to regenerate photoresponsiveness following bleaching by light. To explore the hypothesis that melanopsin in humans expresses the properties of a bistable photopigment in vivo we used the pupillary light reflex (PLR) as a tool but with methods designed to study invertebrate photoreceptors. We show that the pupil only attains a fully stabilized state of constriction after several minutes of light exposure, a feature that is consistent with typical IRP photoequilibrium spectra. We further demonstrate that previous exposure to long wavelength light increases, while short wavelength light decreases the amplitude of pupil constriction, a fundamental property of IRP difference spectra. Modelling these responses to invertebrate photopigment templates yields two putative spectra for the underlying R and M photopigment states with peaks at 481 nm and 587 nm respectively. Furthermore, this bistable mechanism may confer a novel form of \"photic memory\" since information of prior light conditions is retained and shapes subsequent responses to light. These results suggest that the human retina exploits fly-like photoreceptive mechanisms that are potentially important for the modulation of non-visual responses to light and highlights the ubiquitous nature of photoswitchable photosensors across living organisms.

• Publisher: CCSD,Public Library of Science,Public Library of Science (PLoS)
• Subject: Adult / Bistability / Bleaching / Brain research / Cones / Cornea - drug effects / Experiments / Exposure / Eye / Female / Glaucoma / Humans / Hypotheses / Invertebrates / Kinetics / Life Sciences / Light / Light Signal Transduction / Male / Melanopsin / Melatonin / Neuroscience/Sensory Systems / Ophthalmology / Photopigments / Photoreceptors / Photosensitivity / Phototransduction / Physiology/Sensory Systems / Pigmentation / Pupil - physiology / Retina / Retina - metabolism / Retinal ganglion cells / Rod Opsins - metabolism / Rod Opsins - physiology / Rods / Sensitivity and Specificity / Signal transduction / Spectra / Spectrophotometry / Stem cells / Tropicamide - pharmacology / Wavelength