id_643. OPPOSING DIURNAL TRAJECTORIES OF DOPAMINE D2 AND MU-OPIOID RECEPTOR AVAILABILITY AND THEIR SEASONAL MODULATION IN THE HUMAN BRAIN
Michal Rafal Zareba1, Juha Rinne2,3, Jarmo Hietala2,3,4, Pirjo Nuutila2,3,5, Lauri Nummenmaa2,3,6, Lihua Sun2,3,7
1 Jaume I University, Department of Basic and Clinical Psychology and Psychobiology, Castellon de la Plana, Spain
2 University of Turku, Turku PET Centre, Turku, Finland
3 Turku University Hospital, Turku PET Centre, Turku, Finland
4 Turku University Hospital, Department of Psychiatry, Turku, Finland
5 Turku University Hospital, Department of Endocrinology, Turku, Finland
6 University of Turku, Department of Psychology, Turku, Finland
7 University of Turku, Turku Collegium for Science, Medicine and Technology, Turku, Finland
INTRODUCTION: Diurnal variability in arousal, motivation and cognitive performance are known to be modulated by seasonal differences in light exposure, with the intricate connections between these phenomena being especially evident in seasonal affective disorder.
AIM(S): Considering the role of the dopaminergic and opioidergic systems in the aforementioned cognitive processes, the current work used a large positron emission tomography (PET) dataset (n = 377) to explore the presence of time-of-day (TOD)-dependent fluctuations in receptor availability, considering the previously reported effects of seasonality and subclinical anxiety.
METHOD(S):
RESULTS: The data revealed decreased dopamine type-2 (D2R) and increased mu-opioid receptor (MOR) availability in the afternoon compared to morning. The impact of the interactions with the seasonal daylength changes was, however, observed only for MOR, mapping onto brain networks implicated in emotion processing, affective regulation and social cognition. Interestingly, the MOR availability in the aforementioned regions was also sensitive to the interactions of TOD and individual anxiety levels.
CONCLUSIONS: As such, the current results reveal the diurnal variability in indices of dopaminergic and opioidergic neurotransmission by highlighting the opposing trajectory between the two systems. Furthermore, the data pinpoints the special role that the opioid system may play in linking together diurnal and seasonal rhythms with affective and anxiety disorders.
FINANCIAL SUPPORT: Michal Rafal Zareba received financial support from the Fundación Balaguer-Gonel Hermanos in the form of a mobility grant. Lauri Nummenmaa was supported by the European Research Council Advanced Grant (101141656).