Voluntary exercise enhances activity rhythms and ameliorates anxiety- and depression-like behaviors in the sand rat model of circadian rhythm-related mood changes

•Diurnal fat sand rats are an advantageous model for circadian effects on mood.•In short photoperiods (SP), sand rats develop depression- and anxiety-like behaviors.•Voluntary exercise in sand rats strengthens circadian activity rhythms.•Voluntary exercise in sand rats ameliorates SP-induced pathological behavior.

Physical exercise is a non-pharmacological treatment for affective disorders. The mechanisms of its effects are unknown although some suggest a relationship to synchronization of circadian rhythms. One way to explore mechanisms is to utilize animal models. We previously demonstrated that the diurnal fat sand rat is an advantageous model for studying the interactions between photoperiods and mood. The current study was designed to evaluate the effects of voluntary exercise on activity rhythms and anxiety and depression-like behaviors in sand rats as a step towards better understanding of the underlying mechanisms.Male sand rats were housed in short photoperiod (SP; 5 h light/19 h dark) or neutral light (NP; 12 h light/12 h dark) regimens for 3 weeks and divided into subgroups with or without running wheels. Activity was monitored for 3 additional weeks and then animals were tested in the elevated plus-maze, the forced swim test and the social interaction test.Activity rhythms were enhanced by the running wheels. As hypothesized, voluntary exercise had significant effects on SP animals' anxiety- and depression-like behaviors but not on NP animals.Results are discussed in the context of interactions between physical exercise, circadian rhythms and mood. We suggest that the sand rat model can be used to explore the underlying mechanism of the effects of physical exercise for mood disorders.