Chronobiology international
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Light treatment has been used as a non-pharmacological tool to help mitigate poor sleep quality frequently found in older people. In order to increase compliance to non-pharmacological light treatments, new, more efficacious light-delivery systems need to be developed. A prototype personal light-treatment device equipped with low brightness blue light-emitting diodes (LEDs) (peak wavelength near 470 nm) was tested for its effectiveness in suppressing nocturnal melatonin, a measure of circadian stimulation. ⋯ The higher level of blue light suppressed melatonin more quickly, to a greater extent over the course of the 90 min exposure period, and maintained suppression after 60 min. The constant exposure of the low-light level resulted in a decrease in nocturnal melatonin suppression for the last sampling time, whereas for the high-light level, suppression continued throughout the entire exposure period. The present study performed with healthy adults suggests that the tested personal light-treatment device might be a practical, comfortable, and effective way to deliver light treatment to those suffering from circadian sleep disorders; however, the acceptance and effectiveness of personal light-treatment devices by older people and by other segments of the population suffering from sleep disorders in a real-life situation need to be directly tested.
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Behavioral rhythms of the Nile tilapia were investigated to better characterize its circadian system. To do so, the locomotor activity patterns of both male and female tilapia reared under a 12:12 h light-dark (LD) cycle were studied, as well as in males the existence of endogenous rhythmicity under free-running conditions (DD and 45 min LD pulses). When exposed to an LD cycle, the daily pattern of activity differed between individuals: some fish were diurnal, some nocturnal, and a few displayed an arrhythmic pattern. ⋯ However, interestingly in this case, activity was always confined to the dark phase. Furthermore, when the LD cycle was reversed, a third of the fish showed gradual resynchronization to the new phase, taking 7-10 days to be completely re-entrained. Taken together, these results suggest the existence of an endogenous circadian oscillator that controls the expression of locomotor activity rhythms in the Nile tilapia, although its anatomical localization remains unknown.