Nose's response to odors more than just a simple sum of parts
Recording of olfactory sensory neurons in mice shows suppression or enhancement of response when odors are mixed

Date:
September 18, 2020
Source:
Kyushu University
Summary:
Based on highly sensitive recordings of neuron activity in the noses
of mice, researchers have found that olfactory sensory neurons can
exhibit suppression or enhancement of response when odors are mixed,
overturning a long-standing view that the response is a simple
sum with more complex processing only happening at later stages.



FULL STORY ==========================================================================
Take a sniff of a freshly poured glass of wine, and the prevailing
scientific thinking would suggest that the harmony of fragrances you
perceive starts with sensory receptors in your nose simply adding up
the individual odors they encounter. However, new research from Kyushu University shows that a much more complex process is occurring, with
some responses being enhanced and others inhibited depending on the
odors present.


==========================================================================
In mammals, the sense of smell starts with the detection of odors by
receptors at the ends of special cells -- called olfactory sensory neurons
-- in the nose. Each of these neurons has just one type of receptor out
of a large repertoire that depends on the species, with humans having
around 400 types and mice around 1,000.

While the brain's processing of sensory information is known to be
important for picking out and synthesizing smells, relatively little
is still known about the processes happening where the odors are first
detected in the nose.

Using recently developed techniques for highly sensitive recording of
the response of the receptors in the noses of living mice, the research
group led by Takeshi Imai, professor in the Graduate School of Medical
Sciences at Kyushu University, has now published in Cell Reports a
deeper understanding of how neurons in the nose react to odors and
their mixtures.

"It has been previously considered that each odor 'activates' a specific
set of receptors, and that the response of neurons in the nose to odor
mixtures is a simple sum of the responses to each component, but now we
have evidence in mice that this is not the case," says Shigenori Inagaki,
the lead author of the paper.

Studying mice that were genetically modified to have their neurons
emit green light depending on the amount of calcium ions in them --
an indicator of activity -- upon absorption of excitation light, the researchers were able to sensitively record the response of the neurons
in the mice's noses using a two- photon microscope.

Based on these recordings, Imai's team found that odors could not
only activate but also suppress the response of the neurons in the
noses of mice, indicating complex interactions are happening well
before the signals reach the olfactory bulb or brain for additional
processing. Furthermore, their experiments showed that mixing of odors
often leads to an enhancement of response through synergy, especially when
they are in relatively low concentrations, or a suppression of response
through antagonism, especially when they are in high concentrations.

The suppression and enhancement processes revealed by this study may
explain why odor mixtures produce very different perceptual outcomes
from their components, and this kind of understanding could aid in the development of methods for the rational design of olfactory experiences,
from pleasant, harmonious smells to deodorizers.

"These results indicate that our perception of odors is being tuned from
the very moment they are detected in the nose," explains Imai. "Possibly,
these findings may explain how the addition of a minor amount of an odor
can have such a major effect on the perceived fragrance, or how different
kinds of odor molecules in a glass of wine produce a nice harmony."

========================================================================== Story Source: Materials provided by Kyushu_University. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Shigenori Inagaki, Ryo Iwata, Masakazu Iwamoto, Takeshi
Imai. Widespread
Inhibition, Antagonism, and Synergy in Mouse Olfactory Sensory
Neurons In Vivo. Cell Reports, 2020; 31 (13): 107814 DOI: 10.1016/
j.celrep.2020.107814 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200918104252.htm

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