Sitaula, A.; Olsen, L.; Mogharrabi, A.; Zarin, A. A.

Neural circuits consist of neurons that differ not only in their neurotransmitter identities but also in the types and subcellular localization of neurotransmitter receptors (NRs) they express. This receptor diversity enables distinct responses to the same neurotransmitter, highlighting the need to understand NR distribution and function to fully interpret circuit logic. Here, we focus on nicotinic acetylcholine receptors (nAChRs), the primary mediators of fast excitatory transmission in the Drosophila central nervous system (CNS). Functional nAChRs are pentamers assembled from a pool of 10 subunits (alpha1-alpha7 and beta1-beta3), yet their in vivo expression and function remain poorly defined. We used T2A-Gal4 lines and endogenous protein tagging to examine nAChR expression in larval motor neurons (MNs) and identified eight subunits expressed in these cells. MN-specific knockdown of individual subunits caused distinct locomotor defects, indicating their functional importance. Co-localization analysis revealed some subunit pairs are frequently co-expressed at the same synapses, while others localize to distinct subcellular domains. Supporting this, double knockdown of co-localized subunits did not worsen locomotor phenotypes compared to single knockdowns, whereas knockdown of non-co-localized subunit pairs produced additive defects. These results suggest that different nAChR subtypes are strategically positioned in discrete synaptic domains within single MNs, where they serve non-redundant roles. Our findings provide new insight into the spatial organization and functional diversity of nAChRs in motor circuits that drive locomotion.