INTRODUCTION: Dopaminergic neurons provide presynaptic input to the circadian clock network in Drosophila melanogaster, positioning dopamine (DA) to gate clock outputs that shape sleep architecture and locomotor rhythmicity. Because sleep fragmentation and circadian disruption are common non-motor symptoms of Parkinson’s disease (PD), we tested how PD-like dopaminergic dysfunction perturbs clock output circuitry, focusing on PDF⁺small ventrolateral neurons (sLNVs) that show day–night structural plasticity

AIM(S): Determine whether reduced DA signaling disrupts(i)day–night remodeling of PDF⁺ sLNv dorsal termini and(ii)phase-specific locomotor and sleep outputs, and to identify DA receptor pathways in PDF neurons

METHOD(S): We chronically reduced DA synthesis by GAL4–UAS knockdown of pale (ple; tyrosine hydroxylase) and quantified sLNv terminal complexity at ZT2 vs ZT14 with locomotor and sleep behavior. To model progression, we compared adults at 7 vs 30 days. To minimize developmental compensation, we induced acute adult DA depletion by feeding 3-iodo-L-tyrosine (3-IY). Dop1R1, Dop1R2, or Dop2R were silenced specifically in PDF neurons to probe receptor contributions

RESULTS: Controls exhibited higher sLNv arbor complexity at ZT2 than ZT14. ple KD abolished this rhythm in terminal complexity. Behaviorally, ple KD reduced total locomotor output and blunted both the evening activity peak and the dawn response, while overall sleep time was largely preserved but became more fragmented during the light phase. These phenotypes strengthened with age. Acute adult DA depletion via 3-IY recapitulated the structural and behavioral signatures of chronic ple knockdown. Receptor inhibition in PDF neurons was used to delineate DA pathways linking dopaminergic input to sLNv remodeling and circadian behavior.

CONCLUSIONS: Across chronic, acute, and neuron-specific manipulations, dopaminergic signaling is required to maintain day–night structural plasticity of PDF⁺ sLNv dorsal termini and to support phase-specific circadian locomotor outputs. Our research provides a mechanistic circuit framework to study PD-linked sleep and circadian dysfunction.

FINANCIAL SUPPORT: This project has received funding from the European Union's HORIZON 2023 research and innovation programme under the Marie Skłodowska-Curie grant nr. 101169474.