Effect of Photoperiod and Lethal Yellow Mutation on Depression-Like Behavior and Expression of Proinflammatory Cytokines in the Hypothalamus in Mice.

We studied the influence of obesity caused by lethal yellow (AY) mutation in the agouti gene, short photoperiod (4/20 h light/darkness), and combination of these factors on depressive-like behavior in the forced swimming test and expression of genes encoding proinflammatory cytokines in the hypothalamus of heterozygous male C57Bl/6-AY/a mice and their wild-type littermate controls (C57Bl/6-a/a). It was shown that AY mutation as well as short photoperiod increased depressive-like behavior in mice. No effect of the interaction of AY mutation and photoperiod on immobility in the forced swimming test was revealed. In wild-type mice, increased depressive-like behavior caused by short photoperiod was accompanied by enhanced expression of Tnf gene. Exposure to short daylight increased the expression of Nos2.