Polyphasic circadian neural circuits drive differential activities in multiple downstream rhythmic centers

Abstract

Circadian clocks align various behaviors such as locomotor activity, sleep/wake, feeding, and mating to times of day that are most adaptive. How rhythmic information in pacemaker circuits is translated to neuronal outputs is not well understood. Here we used brain-wide, 24-hr in vivo calcium imaging in the Drosophila brain and searched for circadian rhythmic activity among identified clusters of dopaminergic (DA) and peptidergic neuroendocrine (PNE) neurons. Such rhythms were widespread and imposed by the PERIOD-dependent clock activity within the [~]150 cell circadian pacemaker network. The rhythms displayed either a Morning, an Evening, or Mid-Day phase. Different sub-groups of circadian pacemakers imposed neural activity rhythms onto different downstream non-clock neurons. Outputs from the canonical M and E pacemakers converged to regulate DA-PPM3 and DA-PAL neurons. E pacemakers regulate the Evening-active DA-PPL1 neurons. In addition to these canonical M and E oscillators, we present evidence for a third dedicated phase occurring at Mid-Day (MD): the l-LNv pacemakers present the MD activity peak and they regulate the MD-active DA-PPM1/2 neurons and three distinct PNE cell types. Thus, the Drosophila circadian pacemaker network is a polyphasic rhythm generator. It presents dedicated M, E and MD phases that are functionally transduced as neuronal outputs to organize diverse daily activity patterns in downstream circuits.