Effects of the C1473G Polymorphism in the Tryptophan Hydroxylase 2 Gene and the Length of Daylight on Behavior in Mice

Abstract

Seasonal depressive disorder occurs in conditions of seasonal reductions in the duration of daylight and is a significant medical, social, and economic problem. The risk of seasonal depressive disorders is linked with impairments to the serotonin system of the brain. Tryptophan hydroxylase 2 (TPH2) is the key enzyme in serotonin synthesis in the brain. The C1473G polymorphism in the gene encoding TPH2 in mice leads to a twofold decrease in the activity of this enzyme in the mouse brain. The aim of the present work was to study the effects of the length of daylight on the behavior of mature males of the congenic strains B6-1473C and B6-1473G, which have high and low levels of TPH2 activity, respectively. Adult males of these strains were kept for one month in conditions of long (14 h) or short (4 h) daylight durations. Being kept in conditions of short daylight had no effect on mean day-round movement activity, food and water consumption, or anxiety in the open field and elevated plus maze tests in either mouse strain, but decreased mean sleep duration (p < 0.002) and active resistance in the forced swimming test (p < 0.01), changes being similar in both strains. Thus, the C1743G polymorphism had no effect on changes in behavior induced in mice by short daylight.