Olfactory neurons adapt to the surrounding environment

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Summary: A study reveals how olfactory neurons adapt to the surrounding environment.

Source: University of Geneva

Olfactory receptors, present on the surface of sensory neurons in the nasal cavity, recognize odorous molecules and relay this information to the brain. How do these neurons manage to detect a wide variability of signals and adapt to different levels of stimulation?

A joint team from the Faculty of Science and the Faculty of Medicine of the University of Geneva (UNIGE) studied the gene expression profile of these neurons in the presence or absence of olfactory stimulation.

The scientists discovered an unsuspected variability in these profiles depending on the olfactory receptor expressed and previous exposure to odors.

These results, to be read in the journal Nature Communicationhighlight a wide range of olfactory neuron identities and their adaptation to the surrounding environment.

In mammals, the perception of odors is ensured by millions of olfactory neurons, located in the mucous membrane of the nasal cavity. These neurons have receptors on their surface capable of binding specifically to an odorant molecule.

Each olfactory neuron expresses only one gene coding for an olfactory receptor, chosen from a repertoire of approximately 450 in humans and 1200 in mice.

When a volatile molecule is recognized by a receptor, it is activated and generates a signal which is transmitted to the olfactory bulb of the brain, a signal which is then translated into smell.

The olfactory system responds to very variable environments and must be able to adapt very quickly. For example, during continuous stimulation by certain odorous molecules, the perceived intensity gradually decreases and sometimes disappears.

The group of Professor Ivan Rodriguez from the Department of Genetics and Evolution of the Faculty of Science, in collaboration with Professor Alan Carleton from the Department of Basic Neurosciences of the Faculty of Medicine, is interested in the adaptive mechanisms of neurons, and in particular neurons olfactory in mice.

In a previous study, scientists had discovered that after stimulation of a receptor by an odorous molecule for less than an hour, the expression of the gene coding for this receptor decreased in the neuron, indicating a very rapid adaptation mechanism. .

Neurons with a specific profile

The biologists pursued this approach and explored the possibility that this adaptation to an olfactory experience not only affects the gene coding for the receptor, but other genes as well.

To do this, the profile of the genes expressed before and after olfactory stimulation was determined in thousands of olfactory neurons by sequencing their messenger RNAs (the molecules which then allow the production of proteins).

“To our surprise, we found that at rest, i.e. in an environment without stimulation, the messenger RNA profiles of mouse olfactory sensory neuron populations are already very different from each other, and are specific to the olfactory receptor they express,” reports Luis Flores Horgue, PhD student in the Department of Genetics and Evolution and co-first author of the study.

Neurons expressing the same receptor not only share that receptor, but also differ in the expression of hundreds of other genes. Genes whose level of expression seems to be directed by the expressed olfactory receptor, which would thus play a dual role.

A molecule modifies the expression of hundreds of genes

The biologists then analyzed the expression of genes in these neurons after stimulation by odorous molecules. They observed that these molecules induce massive changes in gene expression in activated neurons.

Cross-section of the nasal cavity of a mouse (broad view). Within the dense population of olfactory neurons (in blue), olfactory neurons expressing a specific type of receptor (Olfr151) are marked in bright green. Credit: Madlaina Boillat

“While it was thought that the binding of an odorant molecule would only lead to the activation of the corresponding receptor, we discover that olfactory neurons radically change their identity by modulating the expression of hundreds of genes after activation. And this new identity again depends on the expressed receiver. We are faced with an unexpected, massive, rapid and reversible adaptation mechanism,” explains Ivan Rodriguez, corresponding co-author of the study.

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This work reveals that olfactory neurons are not to be considered as sensors simply passing from a resting state to a stimulated state, but that their identity is in permanent evolution, not only according to the receptor expressed but also according to experiences. past.

This discovery adds another level to the complexity and flexibility of the olfactory system. Understanding how this identity is determined will be the next challenge for the Geneva team.

About this olfactory research news

Author: Press office
Source: University of Geneva
Contact: Press service – University of Geneva
Image: The image is credited to Madlaina Boillat

Original research: Free access.
“Transcriptional adaptation of olfactory sensory neurons to GPCR identity and activity” by Luis Flores Horgue et al. Nature Communication


Summary

Transcriptional adaptation of olfactory sensory neurons to GPCR identity and activity

In mammals, chemoperception relies on a diverse set of neural sensors capable of detecting chemicals in the environment and adapting to different levels of stimulation. The contribution of endogenous and external factors to these neuronal identities remains to be determined.

Taking advantage of the parallel lines of coding present in the olfactory system, we explored potential variations in neural identities before and after the olfactory experience.

We found that at rest, the transcriptomic profiles of populations of mouse olfactory sensory neurons are already divergent, specific to the olfactory receptor they express, and are associated with the sequence of the latter. These divergent profiles evolve more in response to the environment, as exposure to odorants leads to reprogramming via modulation of transcription.

These findings highlight a wide range of sensory neuron identities that are present at rest and adapt to the individual’s experience, thus adding to the complexity and flexibility of sensory coding.

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