Exposure to continuous darkness leads to atypical symptoms of seasonal affective disorder in rats

Aim: Prolonged duration of nocturnal melatonin increase has been implicated in the pathogenesis of the seasonal affectivedisorder (SAD) winter depression. This study was designed to investigate behavioral and physiological consequences of constant dark exposure in male rats for its potential application to human affective disorders. Materials and methods: A total of 12 male Wistar-Albino rats (230-290 g) were assigned to control (LD 12:12 h; n = 6) and constant darkness (DD, 10 days; n = 6) groups. Experimental protocol included comparison of behavioral (FST,open field test, and sucrose preference) and physiological (body weight, food intake, and blood glucose level) parameters. Results:While food intake, weight gain, sucrose preference, and locomotor activity were significantly higher in the DD group, blood glucose level was lower in the same group. Depression-like behavioral despair was prominent in the DD group. As compared to control rats, total duration (s) of immobility was longer and swimming and climbing behaviors were shorter in the DD group.Conclusion: Although continuous darkness exposure for 10 days in male rats seems to mimic atypical symptoms of SAD in terms of depression, weight gain, and the increased sucrose preference, such an extrapolation from behavioral changes in nocturnal animals to human circadian disorders needs further verification.