Extremely sparse olfactory inputs are sufficient to mediate innate aversion in Drosophila.

Area of Science:

• Neuroscience
• Olfactory system research
• Animal behavior

Background:

• Innate attraction and aversion to odors are widespread but poorly understood.
• Olfactory receptor neurons (ORNs) in fruit flies relay odor information to projection neurons (PNs).

Purpose of the Study:

• To investigate the role of olfactory receptor neuron (ORN) population activity in olfactory behavior.
• To determine the circuit mechanisms underlying olfactory aversion in Drosophila melanogaster.

Main Methods:

• Developed a genetic strategy to block and restore specific olfactory receptor neuron (ORN) outputs.
• Silenced olfactory receptor neurons (ORNs) and excitatory projection neurons (ePNs) to assess their role in aversion.

Main Results:

• Olfactory aversion was unaffected by silencing many ORNs, with single ORN types mediating aversion.
• Aversion persisted even when most excitatory projection neurons (ePNs) were silenced.
• Single ORN types, previously considered neutral, were sufficient to mediate aversion.

Conclusions:

• Olfactory aversion is robust and may depend on specific ORN activity patterns, not the quantity or identity of activated ORNs.
• The circuit mechanism for olfactory aversion appears qualitatively different from attraction.
• Downstream circuits, including excitatory projection neurons (ePNs), are not essential for mediating aversion.