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"Sniff, sniff, good!"
Dr.
Yoshihiro Yoshihara |
Head,
Laboratory for Neurobiology of Synapse |
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Whether it is the fresh
scent of young leaves in early summer, the sweet smell of fragrant olives in autumn,
the rich aroma of coffee in the morning, or the mouthwatering, juicy smell of
grilled beef, we all unconsciously enjoy a variety of odors via the functioning
of the olfactory system. We, the members of the Laboratory for Neurobiology of
Synapse, enjoy a life of study of the olfactory system by consciously making full
use of our brains and bodies. Now, the story of olfaction and life will begin....
There is No Significant Difference Between Humans and
Paramecia
Olfaction and gustation are collectively called chemical senses. We start an action
by receiving and sensing various chemical substances through the nose or mouth
that come from outside. The mechanism is not much different from that of paramecia.
Paramecia are not able to see or hear, but they can smell. When they sense chemical
substances coming from matter that is vital to their existence (food, etc.), they
start to move in its direction crying joyfully, "Sniff, sniff...good! I likeitlikeitlikeit!"
(possibly). And if they sense a chemical substance that is generated by something
dangerous to them, they scream "Noooo!, I hateithateithateit!" and run away (muchlike
I do). Given these reactions, we find that chemoreception is evolutionarily the
oldest sense.
The Fly: One Tenth the Number of the Mouse
As a child, a familiar summer scene for me was fighting off the ambush of flies
that punctually attacked my lunch. This behavior was no doubt helped by their
keen olfactory senses. The fly is a model creature for genetics, or forward genetics,
that provides us with a royal road beginning with the search for mutants through
to finding causal genes. A number of research studies on mutants, which are incapable
of retaining a memory of odors, have been reported and the genetic cascade of
olfactory memory analyzed. A recent remarkable study revealed that information
about odorants, which flies receive, is transferred to the brain via certain neuronal
pathways and the information is handled in a certain way. Surprisingly enough,
the mechanism is quite similar to our mammalian mechanism. The fundamental principle
behind the wiring pattern among neurons is identical and the number of odorant
receptors in the fly or the number of glomeruli in the olfactory bulb is as small
as one tenth those of the mouse. This proves that the fly is the most suitable
model for olfactory research. So the study on flies is very important, isnŐt it,
Dr. Miura?
What is the Fate of a Mouse that is Unable to Smell?
What rings a bell with the term "mouse" is reverse genetics! A typical model is
a "knock-out" mouse. By creating mice devoid of specific genes through genetic
engineering techniques, we can infer the geneŐs function from an analysis of its
phenotype. The mouse earns a credit in olfactory research as well. One of the
examples is the "knock-out" mouse which was created so that it lacks a particular
gene (adenylyl cyclase III), which assumedly plays an important role in the olfactory
sensory neurons during conversion of odorant molecules into electrical signals.
These mice died immediately after they were born. No milk was found in their stomachs.
They starved to death because they could not smell their motherŐs nipples. That
was the fate of the poor creatures. Dysosmia or olfactory disorder is a matter
of life or death to mice. So the research with mice is very important, isnŐt it,
Dr. Itohara?
The Nose of the Researcher
Now the serious time (more serious I mean -I have been serious, havenŐt I?). Any
researcher must acquire an especially sharp sense of smell, but you donŐt need
to be a perfumer. You simply need a critical sense of smell that allows you to
detect and precisely select the information that is most important and critical
to your research, from among the countless presentations at the Society for Neuroscience.
It is the nose that ensure that you do not miss the real treasures among the daily
experimental results that may often seem strange and undecipherable. Sharpen your
nose for creative research! Me? Well, unfortunately mine suffers from hay fever
and...SNEEZE! Excuse me! |
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