# Dynamic encoding of temperature in the central circadian circuit coordinates physiological activities

## TL;DR

This study reveals how temperature-sensitive neurons in fruit flies help regulate sleep and activity patterns by responding to temperature changes.

## Contribution

The study identifies DN1a neurons as key temperature sensors in the circadian circuit and their role in modulating sleep and activity.

## Key findings

- DN1a neurons are the most sensitive to temperature changes in the circadian circuit.
- The DN1a-E cell circuit controls evening activity in response to cold temperatures.
- The DN1a-DN3 circuit regulates sleep reduction during warm temperatures.

## Abstract

The circadian clock regulates animal physiological activities. How temperature reorganizes circadian-dependent physiological activities remains elusive. Here, using in-vivo two-photon imaging with the temperature control device, we investigated the response of the Drosophila central circadian circuit to temperature variation and identified that DN1as serves as the most sensitive temperature-sensing neurons. The circadian clock gate DN1a’s diurnal temperature response. Trans-synaptic tracing, connectome analysis, and functional imaging data reveal that DN1as bidirectionally targets two circadian neuronal subsets: activity-related E cells and sleep-promoting DN3s. Specifically, behavioral data demonstrate that the DN1a-E cell circuit modulates the evening locomotion peak in response to cold temperature, while the DN1a-DN3 circuit controls the warm temperature-induced nocturnal sleep reduction. Our findings systematically and comprehensively illustrate how the central circadian circuit dynamically integrates temperature and light signals to effectively coordinate wakefulness and sleep at different times of the day, shedding light on the conserved neural mechanisms underlying temperature-regulated circadian physiology in animals.

The central circadian circuit’s role in integrating temperature changes is not fully understood. Here, the authors demonstrate that temperature-sensitive DN1a circadian neurons in the Drosophila brain bidirectionally influence downstream circadian neurons, regulating temperature-dependent physiological activities.