Abstract
Visible light is the principal stimulus for resetting the mammalian central circadian pacemaker. Circadian phase resetting is most sensitive to short-wavelength (blue) visible light. We examined the effects of removing short-wavelengths < 500 nm from polychromatic white light using optical filters on circadian phase resetting in rats. Under high irradiance conditions, both long- (7 h) and short- (1 h) duration short-wavelength filtered (< 500 nm) light exposure attenuated phase-delay shifts in locomotor activity rhythms by (∼40–50%) as compared to unfiltered light exposure. However, there was no attenuation in phase resetting under low irradiance conditions. Additionally, the reduction in phase-delay shifts corresponded to regionally specific attenuation in molecular markers of pacemaker activation in response to light exposure, including c-FOS, Per1 and Per2. These results demonstrate that removing short-wavelengths from polychromatic white light can attenuate circadian phase resetting in an irradiance dependent manner. These results have important implications for designing and optimizing lighting interventions to enhance circadian adaptation.
Highlights
Circadian misalignment is associated with long-term health problems ranging from depression (Hickie and Rogers, 2011; Rajaratnam et al, 2011) to diabetes (Morris et al, 2015)
In the 1-h exposure condition at CT 16, phase shifts were significantly reduced by ∼50% in the < 500 nm filtered light (FL: -1.01 ± 0.14 h; p = 0.012) compared to the unfiltered light exposure group (UL: −2.02 ± 0.22 h) (Figures 2A,D)
Non-visual responses to ocular light exposure including changes in hormone secretion and phase shifts in locomotor activity rhythms have a peak sensitivity to short-wavelength visible light and are mediated via Intrinsically photosensitive retinal ganglion cells (ipRGCs) primarily through the photopigment melanopsin (Takahashi et al, 1984; Boulos, 1995; Brainard et al, 2001; Thapan et al, 2001; Lockley et al, 2003, 2006; Cajochen et al, 2005; Bedrosian et al, 2013)
Summary
Circadian misalignment is associated with long-term health problems ranging from depression (Hickie and Rogers, 2011; Rajaratnam et al, 2011) to diabetes (Morris et al, 2015). Repeated changes in the light-dark schedule, as is common in shift work, can induce circadian misalignment (James et al, 2007; Skene et al, 2018). Light is the strongest environmental time cue for synchronizing the endogenous pacemaker in the suprachiasmatic nuclei (SCN) (Duffy et al, 1996; Czeisler and Gooley, 2007) and controlling the light-dark schedule can attenuate circadian misalignment (Czeisler et al, 1990; Santhi et al, 2005; Santhi et al, 2007). One of the major operational challenges in controlling the light-dark schedule is avoiding light exposure at Circadian Resetting Under Spectrally-Tuned Light inappropriate times. Modulating the characteristics of light such as intensity and spectrum may provide a mechanism to control the disruptive effects of aberrant light exposure on circadian rhythms
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