Distinct Receptors for a Promiscuous RFamide Neuropeptide Co-Regulate a Distributed Circuit for Locomotory Arousal in C. Elegans.

Neuropeptides modulate brain function by acting as ligands for a wide range of receptors. Systematic pharmacological screening efforts revealed extensive promiscuity in peptide-receptor pairs. However, the endogenous receptors and functions of promiscuous neuropeptides remain poorly understood. Here, we investigated how the Caenorhabditis elegans promiscuous RFamide-peptide FLP-14 and its receptors modulate a circuit for O2-evoked locomotory arousal. We show that FLP-14 peptides released from O2-sensing neurons and interneurons attenuate O2-evoked arousal by acting on three phylogenetically diverse G protein-coupled receptors (DMSR-3, FRPR-8, and NPR-40). Loss of each receptor individually confers strong hyperarousal by O2 comparable to the loss of flp-14. Distinct FLP-14 receptors have non-redundant roles in different target cells, including RID and RIM interneurons, that correlate antagonistically with locomotory arousal. Our results show that FLP-14 signaling requires coordinated modulation of multiple circuit nodes through distinct receptors in attenuating O2-evoked arousal. This promiscuous RFamide peptide network is reminiscent of monoaminergic neuromodulatory networks, which shape behavior through multiple receptors that differentially regulate distributed target neurons.