Constant light and single housing alter novelty-induced locomotor activity and sociability in female Swiss Webster mice.

Objective: Light exposure at night is known to produce behavioral aberrations in both human and animal models. One way to mimic light-at-night is through constant light exposure (LL), wherein animals are placed in an environment where a dark phase never occurs. Additionally, the type of housing condition for the rodents in experiments - grouped-housed vs singly-housed - can produce different behavioral responses, even in female mice. This study investigated whether LL produces alterations to emotionality and sociability, and whether group housing can alleviate some of those negative behavioral outcomes in female mice.

Methods: Female Swiss Webster mice were placed into group or single housing conditions and either into a standard 12:12 light:dark cycle or LL. Novelty-induced (open-field, light-dark box) and circadian locomotor activity, sociability, and serum oxytocin were measured during the middle of the day.

Results: LL and group-housing produced alterations to circadian home-cage activity and increases novelty-induced locomotor activity in the open-field and light-dark box. LL led to increased aggression in both group-housed and single-housed mice, while single-housed/LL mice showed reduced encounters towards the social mouse. Group-housed/LL mice exhibited increased interactions with the empty enclosure. Additionally, both LL and group-housing increased oxytocin levels.

Conclusions: The increase in oxytocin may be a contributing factor to why female mice exhibit increased aggression and other impaired social behaviors in LL. Socialization via group housing was ineffective in reducing the negative sociability seen in mice under LL. These results indicate that aberrant light exposure and circadian misalignment are correlated with impaired social behaviors and emotionality.