Abstract
The core clock circuit is comprised of a small number of distinct groups of neurons in Drosophila melanogaster. Each group interacts with others to sense and integrate external cues from the environment and to give rise to a diurnal circadian behavior. Previous studies have shown that the PDF positive small-Ventral lateral neurons (s-LNvs) are the major pacemakers that integrate light information to set the rhythm and are also responsible for the morning activity in LD. The lateral dorsal neurons (LNds) and 5th s-LNv (PDF negative) mediate the evening locomotor activity, and the dorsal neurons 1 (DN1s) mediate the midday siesta. However, the roles of other circadian neuron groups are not well known.\r \r In this study, we describe a novel role for the DN3 group. By using opto- and thermogenetic tools, we show that some of these DN3 neurons are involved in promoting sleep, and they also can affect the timing of the evening locomotor activity peak. This might indicate that the DN3s are involved in the light-photoperiod circuit.\r \r The s-LNvs that are responsible for the morning activity (M-cells) are also responsible for maintaining rhythms in constant darkness (DD). Light-induced phase shifting behavior is dependent on blue light sensitive photoreceptor, CRY, and it has been published that light activation of CRY fires the LNs, resulting in a phase reset. However, this phenomenon of phase resetting is independent of CRY in the dark and may even be enhanced without CRY. In this study, we describe a novel role of CRY in the dark by using optogenetic mediated firing of pacemaker neurons. CRY seems to decrease membrane potential and therefore reduces neuronal excitability. We therefore suggest that light causes disinhibition and thereby facilitates neuronal depolarization, to start a new circadian cycle.