Abstract
Odorants activate receptors in the peripheral olfactory neurons, which sends information to higher brain centers where behavioral valence is determined. Movement and airflow continuously change what odor plumes an animal encounters and little is known about the effect one plume has on the detection of another. Using the simple Drosophila melanogaster larval model to study this relationship we identify an unexpected phenomenon: response to an attractant can be selectively blocked by previous exposure to some odorants that activates the same receptor. At a mechanistic level, we find that exposure to this type of odorant causes prolonged tonic responses from a receptor (Or42b), which can block subsequent detection of a strong activator of that same receptor. We identify naturally occurring odorants with prolonged tonic responses for other odorant receptors (Ors) as well, suggesting that termination-kinetics is a factor for olfactory coding mechanisms. This mechanism has implications for odor-coding in any system and for designing applications to modify odor-driven behaviors.
Highlights
Animals are constantly exposed to a changing landscape of complex olfactory cues and decision-making within such complex odor environments is critical for navigation behaviors such as finding food, determining oviposition sites, avoiding predators, and identifying mates
We show that two odorants that activate Or42b can have drastically different behavioral outputs for a second odorant tested shortly after, depending upon the temporal kinetics of the initial response
The prolonged response appears stronger than even activity evoked by a continuous odor pulse of 30-secs[10] and appears similar to a class of pyrizine ligands identified for Or33a and Or59b13
Summary
Animals are constantly exposed to a changing landscape of complex olfactory cues and decision-making within such complex odor environments is critical for navigation behaviors such as finding food, determining oviposition sites, avoiding predators, and identifying mates. The olfactory system is responsible for detecting chemical cues in the environment and conveying that information to the brain so that valence – attractiveness or repellency - can be determined. In both vertebrates and flies, primary olfactory neurons (ORNs) are highly specialized cells that typically express single or few receptor proteins[1,2,3]. We show that two odorants that activate Or42b can have drastically different behavioral outputs for a second odorant tested shortly after, depending upon the temporal kinetics of the initial response In this manner, the strong positive valence of this channel can be greatly impacted by prior odor exposures. These findings together have implications in understanding basic principles of odor coding in animals as well as for designing odor-based interventions to modify behavior
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