Working to Understand Circadian Rhythms

The circadian rhythm is a cycle that biological organisms go through every 24 hours. This rhythm is associated with many important homeostatic processes that organisms are responsible for maintaining every day. Some of these functions include sleep/wake cycles, feeding and reproductive behaviors. This rhythm is regulated by a complicated interconnected system that is made up of genes, neurotransmitters, hormones, and sensory input from the organism’s environment (i.e. food and light levels). Researcher Dr. Dreyer and colleagues published a paper in 2019, “A Circadian Output Center Controlling Feeding:Fasting Rhythms in Drosophila”, which focused on researching areas of the Drosophila brain that are downstream or output regions from the Clock centers in the brain. An area of focus in the Drosophila brain was the pars intercerebralis, which is analogous to the human hypothalamic brain region. The researchers found that Drosophila Insulin Like Peptides were important for the regulation of feeding amounts, but not the regulation of feeding:fasting rhythms (Dreyer). The regulation of feeding:fasting rhythms was instead controlled by the SIFamide neuropeptide (Dreyer).

Another set of researchers including Dr. Priya Crosby wrote a research article “Insulin/IGF-1 Drives PERIOD Synthesis to Entrain Circadian Rhythms with Feeding Time” published in May 2019, which demonstrates the effects of insulin in mammals on their circadian rhythms. The results of their studies showed that insulin induced the production of PER2:LUC, which through previous research has been shown to help reset the circadian rhythm (Crosby). The researchers were also able to demonstrate that IGF-1 was relevant to the induction of PER2:LUC production (Crosby). They tested the suprachiasmatic nucleus (SCN), a region of the brain known for its importance in circadian rhythm regulation, which showed insulin receptors, specifically on the lateral aspect, that were reset by insulin (Crosby). This resetting in the SCN only showed results when the cells had been previously treated with tetrodotoxin in order to uncouple the cells from other networks (Crosby). The results of this study demonstrate the importance of insulin in the regulation of proteins that are essential to the circadian rhythm network in mammals. This study emphasizes how important a good scientific understanding of the circadian rhythm is so that when it becomes disordered (commonly seen in shift work), issues can be resolved.

Circadian rhythm research is incredibly important because there are so many biological functions that are regulated by them. Disruptions in the circadian rhythm can cause focus and memory issues, weight change, cognitive impairment, mood issues, body temperature misalignment, and difficulties at school or work. Disruptions in circadian rhythm are often caused by nontraditional shift work, which affects one out of every five employees in the working world (Wickwire). Having a better understanding of the neuronal pathways and the mechanisms that the body uses to maintain the circadian rhythms will allow scientists to find helpful treatments for the side effects of a disrupted circadian rhythm.

Sources:

Crosby, Priya, et al. “Insulin/IGF-1 Drives PERIOD Synthesis to Entrain Circadian Rhythms with Feeding Time.” Cell, vol. 177, no. 4, 2019, pp. 896–909.e20.

Dreyer, Austin P, et al. “A Circadian Output Center Controlling Feeding:Fasting Rhythms in Drosophila.” PLoS Genetics, vol. 15, no. 11, 2019, p. e1008478.

Wickwire, Emerson M., et al. “Shift Work and Shift Work Sleep Disorder Clinical and Organizational Perspectives.” Chest, vol. 151, no. 5, 2017, pp. 1156–1172.