Abstract
Light has direct effects on sleep and wakefulness causing arousal in diurnal animals and sleep in nocturnal animals. In the present study, we assessed the modulation of light-induced sleep by melanopsin and the histaminergic system by exposing mice to millisecond light flashes and continuous light respectively. First, we show that the induction of sleep by millisecond light flashes is dose dependent as a function of light flash number. We found that exposure to 60 flashes of light occurring once every 60 seconds for 1-h (120-ms of total light over an hour) induced a similar amount of sleep as a continuous bright light pulse. Secondly, the induction of sleep by millisecond light flashes was attenuated in the absence of melanopsin when animals were presented with flashes occurring every 60 seconds over a 3-h period beginning at ZT13. Lastly, the acute administration of a histamine H3 autoreceptor antagonist, ciproxifan, blocked the induction of sleep by a 1-h continuous light pulse during the dark period. Ciproxifan caused a decrease in NREMS delta power and an increase in theta activity during both sleep and wake periods respectively. The data suggest that some form of temporal integration occurs in response to millisecond light flashes, and that this process requires melanopsin photoreception. Furthermore, the pharmacological data suggest that the increase of histaminergic neurotransmission is sufficient to attenuate the light-induced sleep response during the dark period.
Highlights
Light serves as an important regulator of behavior and physiology in mammals
We first assessed the ability of millisecond light flashes to induce sleep early in the dark period
A one-way repeated measures ANOVA revealed a significant effect of flash number on total sleep (F(4,28) = 18.5; p < 0.0001) and nonrapid eye movement sleep (NREMS) (F(4,28) = 11.0; p < 0.0001)
Summary
A key example of this is the circadian system which is entrained by light and, in turn, influences the timing of sleep and wake, locomotor activity, and hormone production [1]. A light pulse during the dark phase suppresses locomotor activity (negative masking) and rapidly induces sleep in both a phase dependent and dose-dependent manner [2,3,4]. Melanopsin and Histamine Modulation of Light-Induced Sleep eye serves as the only input of photic information into the brain [5]. The rod, cone, and melanopsin photoreceptors in the eye give mammals the ability to perform both image and nonimage forming functions ranging from the pupillary light reflex to sleep induction in mice [6,7,8,9,10,11]
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