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Title: Brain Serotonin Production Directly Related To Degree Of Sunlight

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Lancet 2002; 360: 1840-42.
12/05/2002 07:02:00 PM
By Harvey McConnell

Turnover of serotonin by the brain is lowest in winter with the rate of production by the brain directly related to the prevailing duration of bright sunlight, Australian researchers have found. Direct measurements of blood from the brain was used by Dr Kristen Boschma and colleagues at the Baker Heart Research Institute, Melbourne, in a search for stronger evidence for the role of serotonin in mood disorders. They investigated a contradiction: the use of phototherapy and serotonin reuptake inhibitors suggest that serotonin itself plays a role in development of seasonal depression. However, concentrations of serotonin and other neurotransmitters, including dopamine and norepinephrine, are normal in the cerebrospinal fluid of patients with seasonal affective disorder. The researchers looked at measuring serotonin concentrations from blood vessels draining the brain--a more accurate way of measuring serotonin concentrations in the brain than by analysis of cerebrospinal fluid. In a cohort of 101 healthy men, aged between 18 and 79, percutaneously placed central venous and arterial catheters high in an internal jugular vein directly sampled venous blood from the brain. This allowed researchers to measure overflow of neurotransmitters and metabolites into the internal jugular venous effluent. Relation between concentration of serotonin metabolite and weather conditions and season were obtained from the Australian Commonwealth Bureau of Meteorology. The data included daily high and low temperatures, mean atmospheric pressures, total rainfall, and hours of bright sunlight. Dr Boschma and colleagues found, irrespective of the month of the year, turnover of serotonin in the brain was affected by acute changes in luminosity, with values being higher on bright days than on dull days There was no significant association between brain serotonin turnover and any of the other environmental factors they examined. The researchers conclude: "Our observations suggest that the prevailing amount of sunlight affects brain serotonergic activity, and thus underlies mood seasonality and seasonal affective disorder, although we do not know whether patients predisposed to affective disorders are affected by environmental factors in the same way as our healthy volunteers."

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