The amount of light exposure can have a profound effect on an individual’s sleep pattern. Stronger light intensity enables noradrenergic locus coeruleus (LC) neurons, which regulate arousal, to function normally and, therefore, provide a circadian regulation of the sleep-wake cycle. Light deprivation, on the other hand, induces a loss of noradrenergic fibers, which, in turn, throws a person’s sleep-wake rhythm out of kilter, a study published in the October 1 issue of the journal SLEEP said.

The study, conducted by Mónica M.C.  González, PhD, and Gary Aston-Jones, PhD, of the University of Pennsylvania, Philadelphia, focused on rats that were maintained on a light-dark (LD) schedule or in constant darkness (DD) for 3 to 4 weeks, and treated with DSP-4, a neurotoxic agent specific for noradrenergic-LC projections. Vigilance states were analyzed before and 3 weeks after LC lesion. The DSP-4 lesion was verified by the immunohistochemistry of noradrenergic fibers in the frontal cortex.

“DSP-4 decreased the amplitude of the sleep-wake rhythm in LD animals by significantly decreasing wakefulness and increasing sleep during the active period,” the authors wrote. “However, DSP-4 had no effect on the sleep-wake cycle of DD animals. Moreover, DD itself decreased the amplitude of the sleep-wake cycle similar to that of the neurotoxic lesion of the noradrenergic system in LD animals.”