Abstract
Normal subjects with bipolarity phenotype, even though not diagnosed bipolar disorder, are known to show distinct properties. In this study, we investigate the changes in molecular circadian rhythm after bright light exposure before sleep in normal subjects with bipolarity phenotype. 25 young male subjects were divided to 14 for bipolarity group and 11 for non-bipolarity group after scoring of the mood disorder questionnaire (MDQ). During the first two study days, the subjects were exposed to the normal-living light (150 lux) for 2.5 hours before sleep, and the saliva and buccal cells of subjects were collected for a total six regular times periodically. During the subsequent five days, the subjects were exposed to the bright light (1,000 lux), and the saliva and buccal cells were collected in the same way. The molecular circadian rhythm of cortisol and circadian gene expression ratio (Per1/Bmal1) were analyzed with cosinor regression. Circadian rhythm of cortisol showed a delay of acrophase in both groups after bright light exposure (p<0.001), and bipolarity group showed a significant delay than non-bipolar group (p=0.008). Circadian rhythm of circadian gene expression ratio showed a delay of acrophase (p<0.001) and a decrease of amplitude (p<0.001) after bright light exposure in both groups, but there was no group difference. Bipolarity group showed hypersensitivity in cortisol rhythm than non-bipolarity group after bright light exposure, but not in circadian gene expression. These results suggest that the characteristic molecular circadian rhythm change of bipolarity group may be related to the biological process after circadian gene expression.
Keywords: bipolarity, circadian rhythm, cortisol, circadian gene, light exposure