Sunshine-exposure variation of human striatal dopamine D₂/D₃ receptor availability in healthy volunteers

Background: In addition to the serotonergic system, the central dopaminergic system has been reported to be correlated with seasonality. The aim of this study was to explore the difference in striatal dopamine D₂/D₃ receptor availability between healthy volunteers who had a high-sunshine exposure and those who had a low exposure. Methods: Sixty-eight participants were enrolled, and those in the upper and lower quartiles in terms of sunshine exposure were categorized into high- (n=17) and low-sunshine-exposure (n=18) subgroups. Single photon emission computed tomography with [¹²³I] iodo-benzamide was used to measure striatal dopamine D₂/D₃ receptor availability. Results: Striatal dopamine D₂/D₃ receptor availability was significantly greater in the subjects with high-sunshine exposure than in those with low-sunshine exposure (F=7.97, p=0.01) after controlling for age, sex, and smoking status. Limitations: Different subjects were examined at different time points in our study. In addition, the sex and tobacco use distributions differed between groups. Conclusion: The central dopaminergic system may play a role in the neurobiological characteristics of sunshine-exposure variation.