A Neuropeptidergic Signaling Pathway for Olfactory Gain Modulation

Sensory systems are dynamically adjusted according to the animals ongoing needs by neuromodulators, such as neuropeptides. Although many neuropeptides are often widely-distributed throughout sensory networks, it is unclear whether such neuropeptides uniformly modulate network activity. Here, we leverage the numerically tractable primary olfactory center of Drosophila (the antennal lobe, AL) to resolve whether one such widely-distributed neuropeptide (myoinhibitory peptide, MIP) uniformly modulates AL processing. We find that despite being uniformly distributed across the AL, MIP decreases olfactory input to some glomeruli, while simultaneously increasing olfactory input to other glomeruli. We reveal that a heterogeneous ensemble of local interneurons (LNs) are the sole source of MIP within the AL. Through high-resolution connectomic analyses, as well as in vivo physiology, we find that the non-uniform effects of MIP are not likely due to MIPergic LN intrinsic properties (e.g., synaptic inputs/outputs, odor-evoked responses, etc.). Instead, we show that differential expression of the inhibitory MIP receptor (sex peptide receptor, SPR) across glomeruli allows MIP to act on distinct intraglomerular substrates, thus enabling differential modulation of olfactory input. Our findings demonstrate how even a seemingly simple case of modulation (i.e., a single neuropeptide acting through a single receptor) can have complex consequences on network processing by acting non-uniformly within different components of the overall network.