A study published in Current Biology reveals new insights into the function of circadian network neurons that undergo daily structural change. 

Circadian networks are collections of neurons that serve as master body clocks in all animals, helping them know when to sleep and when to be productive. Scientists have long studied the circadian networks of the Drosophila melanogaster (better known as the fruit fly) to gain insight into how the human body clock operates. Recently, investigators at the Advanced Science Research Center at The Graduate Center, CUNY (CUNY ASRC) and Barnard College examined the function of small regions of important neuronal clocks in the fly’s brain.

Some segments of the neurons in these regions undergo daily remodeling, displaying a highly branched structure at the beginning of the day and a simpler structure at the beginning of the night. Scientists previously believed that these segments — called the dorsal medial termini — served a critical output function, sending signals that tell the fruit fly’s brain what time of day it is. But the research team discovered that they actually serve in an input capacity, receiving cues from the external environment about the time of day.

“The circadian network shapes the timing of sleep and activity through two key mechanisms: an endogenous clock, which runs on a cycle that is slightly longer or shorter than the Earth’s 24-hour solar day; and the process of entrainment, which adjusts the endogenous clock every day to keep it in sync with the solar day,” said Orie Shafer, a professor with the CUNY ASRC Neuroscience Initiative and the study’s co-senior investigator.

“For years, the field has assumed that the dorsal medial termini would be required for a strong endogenous clock. But when we tested this prediction in flies in which the formation of these segments was prevented, we found the flies’ clocks were absolutely fine but that they had a difficult time synchronizing them to the rising and falling of environmental temperatures.”

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