As part of the Daylight Awareness Week (13-17th of November 2023), Prof. Russell Foster (Head of the Nuffield Laboratory of Ophthalmology, and Director of the Sleep and Circadian Neuroscience Institute at the University of Oxford) talks about the differential impact of daylight and electric light on health. In the first part, we cover the basics of how daylight has shaped life on Earth and how it changes over the course of a 24-hour day. Prof. Foster further explains how light sets our inner time, the so-called circadian clock, and how light can influence sleep, alertness, cognitive performance, cardiovascular and metabolic health.

More information about the Daylight Awareness Week: https://daylight.academy/daylight-awareness-week-2023/

Chapters:

(0:00:00) Intro & Daylight Awareness Week

(0:02:20) Topics of this episode series

(0:04:34) Introducing Russell Foster

(0:11:22) Evolution through daylight

(0:16:38) Physical properties of light

(0:26:02) Discovery of how light sets the circadian clock

(0:37:01) Central & peripheral clocks

(0:41:00) Melatonin is the darkness hormone

(0:48:05) Physiological modulation by light

(0:53:05) Outro & Teaser to Part 2

Russell Foster's recently published book: "Lifetime"

Papers/books that Russell refers to:

"Spectral Sensitivity Tuning in the Deep-Sea" (Douglas et al. 2003)

https://link.springer.com/chapter/10.1007/978-0-387-22628-6_17

J. N. Lythgoe's book: "The Ecology of Vision"

"Sensitivity and integration in a visual pathway for circadian entrainment in the hamster (Mesocricetus auratus)" (Nelson & Takahashi 1991)

https://doi.org/10.1113/jphysiol.1991.sp018660

"Phase-dependent shift of free-running human circadian rhythms in response to a single bright pulse" (Honma et al. 1987)

https://link.springer.com/article/10.1007/BF01945525

"Phototransduction by Retinal Ganglion Cells That Set the Circadian Clock" (Berson et al. 2002)

https://doi.org/10.1126/science.1067262

Russell's group to demonstrate the existence of retinal ganglion cells in mice:

"Melanopsin retinal ganglion cells and the maintenance of circadian and pupillary responses to light in aged rodless/coneless (rd/rd cl) mice" (Semo et al. 2003)

https://doi.org/10.1046/j.1460-9568.2003.02616.x

Retinal ganglion cells in the macaque:

"Melanopsin-expressing ganglion cells in primate retina signal colour and irradiance and project to the LGN" (Dacey et al. 2005)

https://www.nature.com/articles/nature03387

Skin of frogs, melanophores --> melanopsin

"Melanopsin: An opsin in melanophores, brain, and eye" (Provencio et al. 1998)

https://pubmed.ncbi.nlm.nih.gov/9419377/

VA opsin only in fish, not in mammals

"A novel and ancient vertebrate opsin" (Soni & Foster 1998)

https://doi.org/10.1016/S0014-5793(97)00287-1

Samer Hattar’s work: projections to the hypothalamus from melanopsin

"Central projections of melanopsin-expressing retinal ganglion cells in the mouse" (Hattar et al. 2006)

https://doi.org/10.1002/cne.20970

"Circadian photoreception in the retinally degenerate mouse (rd/rd)" (Foster et al. 1991)

https://link.springer.com/article/10.1007/BF00198171

"Neural Reprogramming in Retinal Degeneration" (Marc et al. 2007)

https://doi.org/10.1167/iovs.07-0032

"Suprachiasmatic nucleus in the mouse: retinal innervation, intrinsic organization and efferent projections" (Abrahamson & Moore 2001)

https://doi.org/10.1016/S0006-8993(01)02890-6

Martin Ralph's tau mutant hamster, restore rhythms to the period of the donor:

"Transplanted suprachiasmatic nucleus determines circadian period" (Ralph et al. 1990)

https://www.science.org/doi/abs/10.1126/science.2305266

Peripheral clocks concept shown by Uli Schibler's group in fibroblasts:

"Resetting of Circadian Time in Peripheral Tissues by Glucocorticoid Signaling" (Balsalobre et al. 2000)

https://www.science.org/doi/10.1126/science.289.5488.2344

Josephine Arendt melatonin pioneer:

"Melatonin as a chronobiotic" (Arendt & Skene 2005)

https://doi.org/10.1016/j.smrv.2004.05.002

Contradictory evidence for the use of melatonin to facilitate the onset of sleep

Example meta-analysis article: "Effects of exogenous melatonin on sleep: a meta-analysis" (Brzezinski et al. 2005)

https://doi.org/10.1016/j.smrv.2004.06.004

Patients on beta-blockers produce less melatonin:

"Influence of beta-blockers on melatonin release" (Stoschitzky et al. 1999)

https://link.springer.com/article/10.1007/s002280050604

How to contact Russell Foster:

Email: russell.foster@eye.ox.ac.uk