Neuropeptide modulation of olfactory sensory neurons. (a) A C. elegans chemosensory neuron releases a neuropeptide, NLP-1, which binds an interneuron-expressed receptor, NPR-11, that in turn suppresses odorevoked responses of the sensory neuron. (b) Drosophila olfactory sensory neurons expressing the same receptor project to target cells in aglomerulus. Local interneurons in the antennal lobe release a tachykininrelated peptide, DTK, that binds its receptor, DTKR, on olfactory sensory neuron axons and suppresses neurotransmitter release from them. (c) In mouse, a similar mechanism is postulated.