Synergistic Impact of Sleep Disturbance and Social Isolation in Adult but Not Adolescent Female Mice.

Sleep quality and social isolation are two of the numerous environmental, social and health-related factors that contribute to major depressive disorder (MDD). In human studies, a strong association has been found between sleep quality and perceived loneliness, with each potentially exacerbating the other. In mouse studies, sleep deprivation is performed on either group-housed or individually housed mice, depending on the protocol, but the effect of social isolation is often not assessed. Here, we aimed to investigate the potential synergistic effects of sleep disturbances and social isolation in adolescent (Postnatal day 36) and young adult (9 weeks old) female mice. The mice were subjected to sleep disturbances for 7 days, consisting of 4 h of sleep restriction during the light phase, while group- or single-housed for 7 days. Both the individual and combined effects of sleep disturbance and social isolation were assessed. Our findings reveal significantly longer immobility in the tail suspension test in young adult mice after 7 days of sleep disturbance + social isolation compared to those in the sleep disturbance + socially housed group. The same effect was not seen with adolescent mice. This interaction between sleep disturbance and social isolation in the young adult group suggests a synergistic effect. In conclusion, single housing of mice can change the behavioural outcome of a sleep disturbance protocol. Further, adolescent mice appeared more resilient to the adverse behavioural effects of sleep disturbance in combination with social isolation than young adult mice.