Drosophila Pacemaker Neurons Require G Protein Signaling and GABAergic Inputs to Generate Twenty-Four Hour Behavioral Rhythms

Intercellular signaling is important for accurate circadian rhythms. In Drosophila, the small ventral lateral neurons (s-LN_vs) are the dominant pacemaker neurons and set the pace of most other clock neurons in constant darkness. Here we show that two distinct G protein signaling pathways are required in LN_vs for 24 hr rhythms. Reducing signaling in LN_vs via the G alpha subunit Gs, which signals via cAMP, or via the G alpha subunit Go, which we show signals via Phospholipase 21c, lengthens the period of behavioral rhythms. In contrast, constitutive Gs or Go signaling makes most flies arrhythmic. Using dissociated LN_vs in culture, we found that Go and the metabotropic GABA_B-R3 receptor are required for the inhibitory effects of GABA on LN_vs and that reduced GABA_B-R3 expression in vivo lengthens period. Although no clock neurons produce GABA, hyperexciting GABAergic neurons disrupts behavioral rhythms and s-LN_v molecular clocks. Therefore, s-LN_vs require GABAergic inputs for 24 hr rhythms.