Functional connectivity and selective odor responses of excitatory local interneurons in Drosophila antennal lobe.

Local interneurons in the Drosophila antennal lobe are thought to play important roles in shaping odor responses. However, the physiological properties of excitatory local interneurons (eLNs) and their connectivity in the antennal lobe remain unclear. We first characterized the firing patterns of krasavietz-Gal4-labeled eLNs (krasavietz eLNs) in response to depolarizing currents. Paired recordings of krasavietz eLNs and PNs showed reciprocal excitatory connections mediated by dendrodendritic cholinergic synapses and gap junctions. Reciprocal connections were also found between two krasavietz eLNs but were rare between krasavietz eLNs and inhibitory LNs. Analysis of response onset latencies showed that krasavietz eLNs received monosynaptic inputs from ORNs. Furthermore, each eLN responded with distinct patterns to different odors, and each odor elicited distinct responses in different eLNs, with specific temporal patterns of spiking, indicating that eLNs serve specific coding functions in addition to global excitation in Drosophila olfactory processing.