Potential antidepressant effect of infrared irradiation has seasonality

This study aimed to explore the seasonality of the antidepressant effect of infrared ray (IR) irradiation.

IR has been found to reduce immobility in the forced swimming test (FST) in mice in the winter, suggesting an antidepressant effect. However, whether IR also possesses antidepressant effects in the summer remains questionable.

Fourteen mice were randomly assigned to the exposure group (n=7) and the control group (n=7). The mice in the exposure group received IR irradiation 60 minutes daily for six weeks in the summer. FSTs and tail suspension tests (TSTs) were administered to the two groups weekly. The mean immobility times in both tests were compared between and within groups.

In both FST and TST, there were no significant differences among the mean immobility times overall. (Repeated measures two-way ANOVA: p=0.648, 0.574, respectively). Weekly comparison between groups revealed no significant differences at baseline (two-sample t-test: t12=-0.743, 0.341, respectively) or at the end of the study (p=0.924, 0.925, respectively). A repeated measures ANOVA showed no significant differences within the exposure group during the study period (p=0.602, 0.465, respectively).

Taken together with the results of the previous study, the present results indicate that the antidepressant effect of IR irradiation has seasonality.