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Circadian clock neurons & environmental conditions

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Comment on "Circadian clock neurons constantly monitor environmental temperature to set sleep timing" by S.Yadlapalli & C. Jiang et al., Nature 2018

Have you ever noticed that you fall asleep faster if you decrease the temperature of your room? But why? S.Yadlapalli & C. Jiang et al. identified the neuronal mechanism behind this process in their Nature paper.

The authors used Drosophila melanogaster – a species of fruit fly with a genome close to the human genome – and performed two-photon calcium imaging experiments to unravel how changes in environmental temperature modulate the activity of clock neurons.

They found that dorsal posterior neurons 1 constantly monitored modest temperature changes and they are inhibited by heating and activated by cooling. The external thermoreceptors located in a segment of the antennae (aristae) and in the body (chordotonal organs) confer the thermal sensitivity to clock neurons. The authors examined the activity of the dorsal posterior neurons 1 in naturalistic environments to analyze the relationship with sleep timing and motor activity. They set up a constant cycling temperature to mimic rising temperatures during the morning and falling temperatures during the evening. Flies slowly and gradually increase their locomotor activity during heating phase through the inhibition of dorsal posterior neurons 1. In contrast, the cooling phase activates clock neurons and precipitates flies into sleep mode.

S.Yadlapalli & C. Jiang revealed how environmental temperature regulates the activity of  the circadian clock neurons and set sleep timing. However, decades of research showed that light affects sleep behavior. Further studies should address how temperature and light intermingle in the control of sleep timing. A better knowledge of sleep control could improve our health as sleep deficit leads to depression, memory deficit, and increased risk of cardiovascular diseases.

Written by Isabelle Arnoux; Edited by Radhika Menon. Featured Image: NGC/Carine Thalman.

Reference: Yadlapalli, S., Jiang, C., Bahle, A. et al. Circadian clock neurons constantly monitor environmental temperature to set sleep timing. Nature 555, 98–102 (2018).

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