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TitlePHYSIOLOGICAL CONSEQUENCES OF CIRCADIAN DISRUPTION BY NIGHTTIME LIGHT ...
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mammalian circadian clock (suprachiasmatic nuclei; SCN). Extrinsic light information

travels directly from the intrinsically photosensitive retina ganglion cells (ipRGCs) to the

SCN via the retinohypothalamic tract (Hattar, Liao, Takao, Berson, & Yau, 2002)

synchronizing daily physiological rhythms to the external light-dark cycle (Reppert &

Weaver, 2002). Aberrant light exposure can disrupt the circadian system creating

desynchrony between internal rhythms and the external environment.

Circadian rhythms are important for many homeostatic functions including those

associated with the immune system (Lange, Dimitrov, & Born, 2010). There are circadian

components to many immunological processes including antigen presentation, toll-like

receptor function, cytokine production, and lymphocyte proliferation (Arjona & Sarkar,

2006; A. C. Silver, Arjona, Walker, & Fikrig, 2012) and many immune cells such as

natural killer cells, macrophages, dendritic cells, and B cells possess molecular clock

mechanisms necessary for self-sustaining oscillations (Arjona & Sarkar, 2005; Keller et

al., 2009; A. C. Silver, Arjona, Hughes, Nitabach, & Fikrig, 2012). This reciprocal

relationship between the circadian system and immune function has led to multiple

studies evaluating the effects of chronic circadian disruption on human physiology. Shift-

workers, who are chronically exposed to LAN, are at increased risk for several

inflammatory disorders including heart disease (Ha & Park, 2005), cancer (Davis &

Mirick, 2006; Schernhammer et al., 2001), disrupted rhythmicity of neuroendocrine

function (such as corticotrophin releasing hormone, glucocorticoids, and prolactin)

(Claustrat, Valatx, Harthe, & Brun, 2008; Persengiev, Kanchev, & Vezenkova, 1991),

metabolic disorders and diabetes, as well as mood disorders (Dumont & Beaulieu, 2007).

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