# Receptors underlying an odorant's valence across concentrations in Drosophila larvae

## TL;DR

This study explores how Drosophila larvae respond to different concentrations of an odorant by activating specific receptors in their olfactory system.

## Contribution

The study identifies specific olfactory receptors responsible for concentration-dependent behavioral responses to an odorant in Drosophila larvae.

## Key findings

- Low concentrations of (E)-2-hexenal activate Or7a, causing aversion in Drosophila larvae.
- Higher concentrations recruit additional receptors like Or42a and Or85c, leading to attraction.
- The larval olfactory system can switch behavioral responses based on odorant concentration.

## Abstract

Odorants interact with receptors expressed in specialized olfactory neurons, and neurons of the same class send their axons to distinct glomeruli in the brain. The stereotypic spatial glomerular activity map generates recognition and the behavioral response for the odorant. The valence of an odorant changes with concentration, typically becoming aversive at higher concentrations. Interestingly, in Drosophila larvae, the odorant (E)-2-hexenal is aversive at low concentrations and attractive at higher concentrations. We investigated the molecular and neural basis of this phenomenon, focusing on how activities of different olfactory neurons conveying opposing effects dictate behaviors. We identified the repellant neuron in the larvae as one expressing the olfactory receptor Or7a, whose activation alone at low concentrations of (E)-2-hexenal elicits an avoidance response in an Or7a-dependent manner. We demonstrate that avoidance can be overcome at higher concentrations by activation of additional neurons that are known to be attractive, most notably odorants that are known activators of Or42a and Or85c. These findings suggest that in the larval stage, the attraction-conveying neurons can overcome the aversion-conveying channels for (E)-2-hexenal.

Summary: An odorant that activates only one odorant receptor, Or7a, in Drosophila larvae becomes strongly attractive at higher concentrations, by recruiting activation of additional odorant receptors.