From genes to circuits and behaviors: Neuropeptides expand the coding potential of the nervous system.

Neuropeptide signaling remodels the composition of a chemosensory circuit and shapes behavior in Caenorhabditis elegans. We reported that the ASE left (ASEL) salt sensory neuron uses a proprotein convertase， BLI-4， to cleave the insulin-like peptide INS-6. INS-6 peptides are released from the ASEL neuron in response to large， but not small changes in salt stimuli. Fast INS-6 signaling functionally transforms the AWC olfactory sensory neuron into an interneuron in the neural circuit for high salt. This new circuit configuration potentiates behavioral attraction to high salt. Here， in the context of genes， circuits， and behaviors， we discuss the diverse modes of neuropeptide processing and signaling， which expand the coding potential of the nervous system. First， neuropeptide processing and release genes prepare insulin peptides to signal in the nervous system. Second， this neuropeptide signaling diversifies the communication of neural circuits and introduces circuit-level flexibility. Finally， the resulting multisensory neurons and circuits drive finely tuned behavioral choices.