Large Ventral Lateral Neurons Modulate Arousal and Sleep in Drosophila

Background: Large ventral lateral clock neurons (ILNvs) exhibit higher daytime-light-driven spontaneous action-potential firing rates in Drosophila, coinciding with wakefulness and locomotor-activity behavior. To determine whether the ILNvs are involved in arousal and sleep/wake behavior, we examined the effects of altered electrical excitation of the LNvs. Results: LNv-hyperexcited flies reverse the normal day-night firing pattern, showing higher ILNv firing rates at night and pigment-dispersing-factor-m ediated enhancement of nocturnal locomotor-activity behavior and reduced quantity and quality of sleep. ILNv hyperexcitation impairs sensory arousal, as shown by physiological and behavioral assays. ILNv-hyperexcited flies lacking sLNvs exhibit robust hyperexcitation-induced increases in nocturnal behavior, suggesting that the sLNvs are not essential for mediation of arousal. Conclusions: Light-activated ILNvs modulate behavioral arousal and sleep in Drosophila.