Night eating model shows time-specific depression-like behavior in the forced swimming test.

The circadian clock system is associated with feeding and mood. Patients with night eating syndrome (NES) delay their eating rhythm and their mood declines during the evening and night, manifesting as time-specific depression. Therefore, we hypothesized that the NES feeding pattern might cause time-specific depression. We established new NES model by restricted feeding with high-fat diet during the inactive period under normal-fat diet ad libitum. The FST (forced swimming test) immobility time in the NES model group was prolonged only after lights-on, corresponding to evening and early night for humans. We examined the effect of the NES feeding pattern on peripheral clocks using PER2::LUCIFERASE knock-in mice and an in vivo monitoring system. Caloric intake during the inactive period would shift the peripheral clock, and might be an important factor in causing the time-specific depression-like behavior. In the NES model group, synthesis of serotonin and norepinephrine were increased, but utilization and metabolism of these monoamines were decreased under stress. Desipramine shortened some mice's FST immobility time in the NES model group. The present study suggests that the NES feeding pattern causes phase shift of peripheral clocks and malfunction of the monoamine system, which may contribute to the development of time-specific depression.