Repeated social stress at night, but not during the day, affects the brain’s internal molecular clock

Mice subjected to repeated social defeat during the dark phase exhibited increased PER2::LUC rhythm amplitude in the brain's circadian center.

• Social defeat during the dark phase led to changes in circadian rhythms in the brain compared to those during the light phase.
• Increased PER2 protein expression was observed in the posterior part of the brain's circadian center in mice exposed to dark-phase stress.
• Mice experiencing social defeat in the light phase showed a 2-hour phase advance in the adrenal gland's circadian rhythm.
• Elevated plasma levels of brain-derived neurotrophic factor (BDNF) were found in light-phase stressed mice, suggesting a potential protective mechanism.
• The molecular rhythmicity in the brain's circadian center was affected by dark-phase stress but not by light-phase stress.

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