Large and small ventral lateral neurons play vital roles in circadian arousal circuits in drosophila melanogaster

Abstract

Neuronal circuits underline various simple and complex behaviours in animals, which are displayed in response to numerous stimuli in the environment. Drosophila melanogaster offers several simple but effective tools in the neurogenetic dissection of different behaviours. We have focused on two related neuronal circuits – the circadian clock network and sleeparousal circuit, and looked to evaluate the roles of two subgroups of circadian clock neurons – the large and small ventral lateral neurons (l-LNv and s-LNv) within these circuits. So far, the l-LNv have mostly been disregarded or have been given a auxiliary role in the hierarchical arrangement of the Drosophila circadian circuit. We aimed to re-evaluate this view by examining the contributions of l-LNv in governing an important clock function – phasing of locomotor activity peaks. Here, we report that electrical activity of l-LNv controls phasing of the evening peak of activity across a range of photoperiods. Further, we propose a model in which lLNv enable adaptation to seasonal changes by regulating the phase of the evening peak. Thus, our results have revealed a critical role for the l-LNv in the clock circuit, where it was erstwhile negligible. In contrast, in the sleep/arousal circuit, the l-LNv play a major role whereas so far, no known role for the s-LNv has been reported. Here, we have reprised the role for l-LNv in the arousal circuit; found novel role for s-LNv in mediating arousal that is modulated by l-LNv and identified a downstream target of the LNv neurons, which is localized in the Pars Intercerebralis, the neuroendocrine centre of the fly brain. Thus, our results underline the flexibility of neuronal function such that certain neurons can play integral roles in otherwise distinct circuits.