A circuit supporting concentration-invariant odor perception in Drosophila

Area of Science:

• Neuroscience
• Olfactory system research
• Insect sensory biology

Background:

• Olfactory perception is often invariant to odor concentration, but underlying neural mechanisms are unclear.
• Drosophila melanogaster larvae utilize 21 olfactory sensory neurons (OSNs) expressing 25 odorant receptors to detect odors.

Purpose of the Study:

• Investigate how subsets of larval OSNs cooperate to enable concentration-invariant odor perception.
• Elucidate the neural integration of information from OSNs with overlapping response properties.

Main Methods:

• Calcium imaging to monitor OSN activation by ethyl butyrate across concentration gradients.
• Characterization of local inhibitory interneuron and projection neuron responses in the antennal lobe.

Main Results:

• Ethyl butyrate activated three OSNs with distinct thresholds across three orders of magnitude.
• Wild-type larvae showed attraction to ethyl butyrate over a 500-fold concentration range.
• Single functional OSN mutants exhibited attraction over narrower ranges; local interneurons activated at high concentrations, and projection neurons showed reduced responses with summed OSN input.

Conclusions:

• Increasing odor concentrations progressively activate concentration-tuned OSNs and recruit inhibitory local interneurons.
• The interplay between combinatorial OSN input and local interneuron activation enables sensitivity to odors across a wide range of intensities.