Effects of Chronic Dim-light-at-night Exposure on Sleep in Young and Aged Mice

Dim-light-at-night (DLAN) exposure is associated with health problems, such as metabolic disruptions, immunological modulations, oxidative stress, sleep problems, and altered circadian timing. Neurophysiological parameters, including sleep patterns, are altered in the course of aging in a similar way. Here, we investigated the effect of chronic (three months) DLAN exposure (12 L:12 Dim-light, 75:5 lux) on sleep and the sleep electroencephalogram (EEG), and rest-activity behavior in young (6-month-old, n = 9) and aged (18- n = 8, 24-month-old, n = 6) C57BL/6J mice and compared with age-matched controls (n = 11, n = 9 and n = 8, respectively). We recorded the EEG and electromyogram continuously for 48-h and conducted a 6-h sleep-deprivation. A delay in the phase angle of entrainment of locomotor activity and daily vigilance state rhythms was apparent in mice following DLAN exposure, throughout the whole age spectrum, rendering sleep characteristics similar among the three age DLAN groups and significantly different from the age-matched controls. Notably, slow-wave-activity in NREM sleep (SWA, EEG power density in 0.5-4.0 Hz) was differentially altered in young and aged DLAN mice. Particularly, SWA increased as a function of age, which was further accentuated following DLAN exposure. However, this was not found in the young DLAN animals, which were characterized by the lowest SWA levels. Concluding, long-term DLAN exposure induced more pronounced alterations in the sleep architecture of young mice, towards an aging phenotype, while it enhanced age-associated sleep changes in the older groups. Our data suggest that irrespective of age, chronic DLAN exposure deteriorates sleep behavior and may consequently impact general health.