Researchers from Washington University in St. Louis identified a subset of neurons involved in setting daily rhythms of the body.
All essential functions of the body are highly synchronized by circadian clock with the local time. The suprachiasmatic nucleus (SCN) is a tiny region situated directly above the optic chiasm in the hypothalamus. It is responsible for controlling circadian rhythms and reminds a person to wake up and go to sleep at a regular time each day. A disturbance in the rhythm majorly due to shift work or crossing time zones leads to jet lags with symptoms of fatigue, disorientation, and insomnia. Now, researchers at Washington University in St Louis suggested that a small subset of SCN neurons are involved in the mechanism of the body clock as it produces vasoactive intestinal polypeptide (VIP), which is used by neurons to communicate and synchronize their daily rhythms with one another. The researchers developed a method to characterize the normal daily firing patterns of VIP neurons. The millisecond-long action potentials recorded for a set of neurons revealed two classes of VIP neurons, namely tonic VIP neurons and VIP irregular neurons. The tonic VIP neurons fired with consistent intervals and VIP irregular neurons fired in doublets or triplets with equally spaced intervals after each doublet or triplet. The research was published online in Neuron on July 12, 2018.
The researchers kept mice in total darkness with no environmental clues of time to determine whether activation of VIP neurons would shift the daily schedule of the SCN and the mice. Optogenetics enabled the activation of VIP neurons at the same time every day. The procedure mimicked flying to a new time zone. It was observed that mice were cured from jet lag effectively with VIP irregular neurons. However, firing of tonic VIP neurons revealed that the mice were slower to adjust to the new local time. The research is expected to help understand ways to encourage VIP neurons to release their VIP to pick the clock’s lock and reduce jet lag for human travelers and shift workers.