The circadian clock is necessary for controlling many important homeostatic functions in our body. In the article, "A circadian output center controlling feeding: fasting rhythms in Drosophila" written by Austin P. Dreyer and colleagues, they examined how distinct pars intercerebralis (PI) cell populations in Drosophila contribute to feeding demonstrating the complex neuronal networks in place. One population of PI cells express Drosophila insulin-like peptides (DILPs) which affect the feeding pattern in fruit flies. Additionally, the nearby PI population has neurons expressing the neuropeptide SIFamide (SIFa) that can degrade feeding if manipulated. The importance of understanding the output pathways in the central neuronal clock can aid in understanding what factors can lead to disruption in sleep or other metabolic disorders. Dreyer et al. found that the PI populations contribute differently to circadian outputs. DH44+ cells selectively regulate rest/activity rhythms while SIFa+ cells impact not only rest/activity rhythms, but also feeding/fasting rhythms. What was the most interesting, that the study found, was the associated signaling population to a neuronal population for the regulation of feeding/fasting habits. If we look at mammals who live in different time zones or in various parts of the globe, the circadian clocks may vary. More importantly, this change in circadian rhythms could impact an animal's feeding behavior.
An article in the New York Times by Veronique Greenwood titled, "Perhaps Santa Had to Shout to His Eight Reindeer Because They Fell Asleep" discusses about Svalbard reindeer that reside on the arctic island of Svalbard in Norway. These reindeer eat incredible amounts of food to store up fat during the winter nights. Additionally, Svalbard reindeer are extraordinary because they can adapt to extreme weather conditions. Many researchers believed that these reindeer lacked a standard circadian rhythm, but a small study by Arnold and colleagues suggest otherwise.
In the article, "Circadian rhythmicity persists through the Polar night and midnight sun in Svalbard reindeer" they discuss how the Svalbard reindeer do have internal clocks, but they work differently. Arnold et al. were able to observe the patterns in body temperature, heart rate, and movement by administering a harmless pill-shaped, metal capsule that contained sensors to track this information in the stomach of reindeer. Dr. Arnold and colleagues observed a diurnal rhythm in body temperature. Additionally, the circadian cycles in these reindeer varied quite rapidly in the months leading up to the summer period, which drives the animals to forage what they can.The circadian clock in the Svalbard reindeer weakens during the summer allowing them to easily ignore their internal clock and eat as much as they can. This allows the reindeer to have enough energy stored before winter arrives. It is understood that humans must eat at certain periods of the day in order to maintain normal functioning of the body. Thus, it is interesting how the metabolism in Svalbard reindeer is unaffected even when they stay up all night consuming food.
Work Cited
Arnold, W., Ruf, T., Loe, L.E. et al. Circadian rhythmicity persists through the Polar night and
midnight sun in Svalbard reindeer. Sci Rep 8, 144466 (2018). https://doi.org/10.1038/s41598- 018-32778-4
Dreyer AP, Martin MM, Fulgham CV, Jabr DA, Bai L, Beshel J, et al. (2019) A circadian output center controlling feeding:fasting rhythms in Drosophila. PLoS Genet 15(11): e1008478. https://doi.org/10.1371/journal.pgen.1008478
Greenwood, Veronique. "Perhaps Santa Had to Shout to His Eight Reindeer Because They Fell Asleep." The New York Times, The New York Times, 24 Dec. 2018, www.nytimes.com/2018/12/24/science/reindeer-body-clock.html?searchResultPosition=1
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