Intercellular signaling is important for accurate circadian rhythms. In Drosophila, the small ventral lateral neurons (s-LNvs) 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 LNvs for 24 hr rhythms. Reducing signaling in LNvs 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 LNvs in culture, we found that Go and the metabotropic GABAB-R3 receptor are required for the inhibitory effects of GABA on LNvs and that reduced GABAB-R3 expression in vivo lengthens period. Although no clock neurons produce GABA, hyperexciting GABAergic neurons disrupts behavioral rhythms and s-LNv molecular clocks. Therefore, s-LNvs require GABAergic inputs for 24 hr rhythms.
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