Daily variation of nociceptive responses in Drosophila.

The circadian clock regulates a wide range of physiological and behavioral rhythms. Daily variation in nociceptive responsiveness to harmful stimuli has been demonstrated in mammalian models; however, whether such variation is present in non-mammalian species including insects has remained unclear. Here, we found that behavioral responses to noxious heat stimuli in the fruit fly Drosophila melanogaster exhibit significant variation throughout the day. In contrast, null mutants for the clock genes per and tim failed to exhibit daily variation in nociceptive responses. Consistently, we found daily changes of calcium responses toward noxious heat in peripheral nociceptive neurons, which is likely to be under the control of the clock gene. Together, our data show the clock gene-dependent daily variation of nociceptive responses in Drosophila, and support a potential model in which sensory systems, including nociception, operate under distinct temporal dynamics, enabling animals to adjust their behavior in response to environmental changes across the day.