Light, Clocks and Sleep: Keeping an eye on the time

We and most organisms possess a 24h biological (circadian) clock which acts to ‘fine-tune’ physiology and behaviour to the varying demands of the day/night cycle. Such a clock is only useful if biological time remains synchronised to solar time, and the daily change in the gross amount of light (irradiance) at dawn or dusk provides the most reliable indicator of the time of day. In mammals the “master clock” is located within small paired nuclei at the base of the brain called the suprachiasmatic nuclei (SCN). The SCN receive direct retinal projections which adjust the clock to the light/dark cycle, and eye loss in mammals blocks this completely. But how does the eye detect this light to provide the re-setting signal? Surprisingly, we found that visually blind mice, with genetic defects in the rods and cones, could still use their eyes to regulate the circadian system. These, and a host of subsequent experiments including studies in humans with genetic defects of the eye, showed that the processing of light information by the circadian and classical visual systems is different and that the mammalian eye contains an additional non-rod, non-cone photoreceptor based upon a small number of photosensitive retinal ganglion cells (pRGCs). These remarkable, and recently discovered receptors use “melanopsin” as their photopigment, which is sensitive in the blue part of the spectrum around 480nm. This presentation will explore the discovery, biology and clinical importance of this third photoreceptor system of the eye.

Russell Foster

About the Speaker:
Russell Foster is Professor of Circadian Neuroscience and the Head of Department of Ophthalmology. He is also a Nicholas Kurti Senior Fellow at Brasenose College. Prior to this, Russell was at Imperial College where Russell was Chair of Molecular Neuroscience within the Faculty of Medicine. Russell Foster’s research spans basic and applied circadian and photoreceptor biology.

He received his education at the University of Bristol under the supervision of Professor Sir Brian Follett. from 1988–1995 he was a member of the National Science Foundation Center for Biological Rhythms at the University of Virginia and worked closely with Michael Menaker. In 1995 he returned to the UK and established his group at Imperial College. For his discovery of non-rod, non-cone ocular photoreceptors he has been awarded the Honma prize (Japan), Cogan award (USA), and Zoological Society Scientific & Edride-Green Medals (UK). He is the co-author of Rhythms of Life, a popular science book on circadian rhythms.