Neurons in the brain's master clock that adjust their activity in response to light have a key role in the resetting of an animal's daily cycle, finds a study of male and female mice published in JNeurosci. These cells may be responsible for circadian rhythm disruptions stemming from exposure to artificial light at night.

By demonstrating in mice that suprachiasmatic nucleus (SCN) neurons expressing the neuropeptide vasoactive intestinal peptide (VIP) exhibit a regular cycle in their activity levels that is disrupted under conditions of constant light, Erik Herzog and colleagues resolve long-standing questions about how the SCN synchronizes the body's daily rhythms to environmental light.

Shifts In Daily Rhythms

Blocking the activity of these neurons reduced the severity of shifts in daily rhythms. These findings suggest a potential mechanism by which the modern advent of light at night may have led to an increased prevalence of sleep disorders.

Daily rhythms in Behavior and Physiology

It includes sleep/wake and hormone release, are synchronized to local time by the master circadian pacemaker, the suprachiasmatic nucleus (SCN). The advent of artificial lighting and, consequently, light exposure at night, is associated with an increased risk of disease due to disrupted circadian rhythms.

However, the mechanisms by which the SCN encodes normal and pathological light information are unclear. Here, we find that vasoactive intestinal peptide (VIP)-producing SCN neurons exhibit daily rhythms in neuronal activity and VIP release and that blocking the activity of these neurons attenuates light-induced phase shifts.

Rhythmic VIP Neurons

The authors conclude that rhythmic VIP neurons are an essential component of the circadian light transduction pathway.