Medical Research Council (MRC) scientists in Scotland have discovered what makes the body's seasonal clock, which affects mood, appetite and energy levels, tick. The finding, published in Current Biology, will help scientists understand how the onset of winter's long evenings drives people to put on weight and become SAD*.
By studying a wild-type breed of Scottish sheep from the Outer Hebrides which has highly seasonal reproduction, scientists from the MRC Human Reproductive Sciences Unit working with colleagues at the University of Aberdeen, discovered that the body's seasonal clockwork is dependent on processes occurring inside individual cells in the brain. It is driven by the way certain genes interact with each other, and this is affected by day length.
Scientists already knew that these genes, called clock genes and clock controlled genes, act as the body's daily time-keepers, and that the timing of when they switch on and off determines, for example, when we wake up, when we feel tired and when we are hungry.
It has now been discovered that the timing of this gene interaction is altered according to the number of hours of darkness. As the nights get longer the time between clock genes peaks is stretched out, and as they get shorter again, with the coming of spring, the interval is squeezed back together. Because our actions and the way we feel is determined by the way genes interact with each other, this gives rise to seasonal cycles in appetite, body weight and behaviour.
Night length affects the timing of the clock genes through the production of a hormone called melatonin. Melatonin is produced when it is dark by the pineal gland in the brain. Long nocturnal melatonin signals register as winter, changing the interval between clock genes.
Lead scientist, Dr Gerald Lincoln, of the MRC's Human Reproductive Sciences Unit, said: "Because our moods, appetites and energy levels are affected by the seasons, unravelling at a molecular level what makes our seasonal clocks tick is important for understanding and treating seasonal and lifestyle related illnesses and diseases."
Dr David Hazlerigg, Senior Lecturer, School of Biological Sciences, University of Aberdeen, who was involved in the study, added: "Our mechanistic understanding of how treatments involving light or melatonin alleviate mood or sleep disorders is rather poor. We hope that our research will help fill this knowledge gap."
Seasonal clocks are widespread in nature, ensuring that cycles in reproduction, moulting, migration, hibernation and other familiar events occur at the appropriate season.
For further information, or to arrange an interview with Dr David Hazlerigg, Senior Lecturer, School of Biological Sciences, please contact him direct on: 01224 272871. Please be advised that Dr Hazlerigg is only available to speak to the media between 2.00-3.00pm today (Tuesday, 17 February). Please do not call him outwith this hour.
For a copy of the paper contact Heidi Hardman in the Cell Press Office on 001 617 397 2879 or 001 857 928 5630.