The wiring diagram of the Drosophila larva olfactory system

Summary

Date: 
March 2, 2016 - 1:00pm
Location: 
Northwest 243
About the Speaker
Name: 
Matt Berck (Samuel Lab)

The sense of smell enables animals to detect and react to long-distance cues according to internalized valences. Odors evoke responses from olfactory receptor neurons (ORNs), whose activities are integrated and processed in olfactory glomeruli and then relayed by projection neurons (PNs) to higher brain centers. We have mapped with serial section electron microscopy the complete wiring diagram of the left and right antennal lobes of Drosophila larva, the first relay of the olfactory system. We found two parallel circuits processing ORN inputs. First, a canonical circuit that consists of uniglomerular PNs that relay gain-controlled ORN inputs to the learning and memory center (mushroom body) and the center for innate behaviors (lateral horn). Second, a novel circuit, where multiglomerular PNs and hierarchically structured local neurons (LNs) extract complex features from odor space and relay them to multiple brain areas. The wiring diagram also suggests a bistable gain control mechanism, which either computes odor saliency through panglomerular inhibition, or allows a subset of glomeruli to respond to faint aversive odors in the presence of strong appetitive odor concentrations. This switch between operational modes is regulated by both neuromodulatory neurons and non-olfactory sensory neurons. To further analyze the antennal lobe circuitry, we have also designed and utilized a microfluidic device to perform in vivo calcium imaging. With this setup, we can visualize which ORNs respond to known olfactory cues at various concentrations, and we can measure the physiologies of downstream neurons to enhance our understanding of the wiring diagram.