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Abstract
Objective. Climate, in particular sunshine, influences mood and energy levels, creating a positive upswing of mood on bright, sunny days and negative downswing in cold, dark winter seasons. Higher serotonin transporter availability in healthy human subjects in times of lesser light exposure and lower serotonin levels have been shown in winter. Methods. We examined the light-dependent variations in serotonin-1A receptor binding in limbic regions in 36 drug-naive healthy human subjects. Receptor binding was quantified using positron emission tomography and the radioligand [carbonyl-11C]WAY-100635. Binding potential values were related to the amount of individual exposure to sunlight (daily duration of sunshine) and global radiation (total light intensity). Results. We found a 20–30% lower serotonin-1A receptor binding in the group exposed to a lower amount of global light radiation. Partial correlation analysis revealed significant positive correlations between the regional postsynaptic serotonin-1A receptor binding and global radiation accumulated over a period of 5 days. Conclusions. Seasonal factors, such as daily amount of sunshine and global radiation, influence serotonin-1A receptor binding in limbic brain regions of healthy human subjects. Combined with recently demonstrated seasonal fluctuations in the serotonin transporter availability, our results underline the importance of seasonal factors in the regulation of the serotonergic transmission.
Acknowledgments
This research was partly supported by grants from the Austrian National Bank (OENB P11468) to R. Lanzenberger and the Austrian Science Fund (FWF P16549). We are grateful to the technical and medical team of the MUW PET Centre, especially to A. Becherer and R. Dudczak. Furthermore, we would like to thank the Central Institute for Meteorology and Geodynamics (ZAMG) in Vienna, Austria, for providing the meteorological data for this study.
Statement of Interest
S. Kasper received grant/research support from Eli Lilly, Lundbeck, Bristol-Myers Squibb, Servier, Sepracor, Glaxo SmithKline, Organon, and has served as a consultant or on advisory boards for Astra Zeneca, Austrian Sick Found, Bristol-Myers Squibb, Glaxo SmithKline, Eli Lily, Lundbeck, Pfizer, Organon, Sepracor, Janssen, and Novartis, and has served on speakers’ bureaus for Astra Zeneca, Eli Lilly, Lundbeck, Servier, Sepracor and Janssen. R. Lanzenberger received travel grants from Lundbeck A/S and Servier, research support from Lundbeck A/S, furthermore conference speaker honoraria from Lundbeck and Astra Zeneca. C. Spindelegger and P. Stein received a travel grant from Lundbeck; M. Willeit received travel grants from several companies in CNS research. U. Moser received travel grants from Bristol-Myers Squibb and Astra Zeneca.