Light pulses administered during the circadian dark phase alter expression of cell cycle associated transcripts in mouse brain (original) (raw)

Acute Light Exposure Suppresses Circadian Rhythms in Clock Gene Expression

Journal of Biological Rhythms, 2011

Circadian arrhythmia can be induced in mammals by several weeks of constant light (Daan and Pittendrigh, 1976) or by a brief light stimulus given at the transition point of the phase response curve (i.e., the singularity point) (Winfree, 1980). More recently, some laboratories have employed novel light treatments that induce circadian arrhythmia in the Siberian hamster (Phodopus sungorus). In these studies, circadian arrhythmia was induced by using a phaseadv ancing light pulse on one night followed by a phase-delaying signal on the next night (Steinlechner et al., 2002; Ruby et al., 2004). Arrhythmia was reported for locomotor activity, body temperature, sleep/ wake cycles, and melatonin levels (Ruby et al., 2004; Steinlechner et al., 2002). The light treatment consistently caused a marked shortening of the active phase (i.e., alpha compression), resulting in arrhythmia within 2 to 5 circadian cycles that persisted despite the continued presence of the light-dark (LD) cycle. We hypothesized that the loss of overt rhythms was due to light-induced arrhythmia in the suprachiasmatic nucleus (SCN) because it is the central circadian LETTER

Nighttime dim light exposure alters the responses of the circadian system

Neuroscience, 2010

The daily light dark cycle is the most salient entraining factor for the circadian system. However, in modern society, darkness at night is vanishing as light pollution steadily increases. The impact of brighter nights on wild life ecology and human physiology is just now being recognized. In the present study, we tested the possible detrimental effects of dim light exposure on the regulation of circadian rhythms, using CD1 mice housed in light/dim light (LdimL, 300 lux:20 lux) or light/dark (LD, 300 lux:1 lux) conditions. We first examined the expression of clock genes in the suprachiasmatic nucleus (SCN), the locus of the principal brain clock, in the animals of the LD and LdimL groups. Under the entrained condition, there was no difference in PER1 peak expression between the two groups, but at the trough of the PER 1 rhythm, there was an increase in PER1 in the LdimL group, indicating a decrease in the amplitude of the PER1 rhythm. After a brief light exposure (30 min, 300 lux) a...