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The “Génome, mémoire et développement”
(Genome, memory and development) team of the CNRS “Développement,
évolution et plasticité du système nerveux”
Laboratory (Development, Evolution and Plasticity of the Nervous System)
has used the model of the Drosophila fly to localize a small region
of the brain specifically involved in long-term memory. The results of
their work are published in Science, November 2, 2001.
The Drosophila has many
advantages which make it a model of choice for researchers. All its genes
are known, thousands of mutants have been isolated, and although its brain
is small, it has certain notable features such as the mushroom bodies
involved in short-term memory. The mushroom bodies are composed of about
5,000 neurons which are propagated in the five lobes -two vertical and
three horizontal- of the brain. The CNRS researchers have brought to light
the essential role of the mushroom bodies in long-term memory, and have
dissected the different lobes to study their functions.
If a group of flies is trained to associate an odor with electric shocks,
they will subsequently tend to avoid this odor, which signals imminent
danger. If this experiment is carried out once it induces memory lasting
several hours. When repeated ten times, with a rest interval of at least
fifteen minutes between each session, the experiment shows that long-term
memory is induced and is detectable for over one week. This long-term
memory shares characteristics with that of mammals.
The method of the Genome, Memory and Development team involved ablating
certain parts of the mushroom bodies to analyze the role of these zones
in short- and long-term memory. The ala mutant Drosophila
has been characterized. These particular mutants have abnormal mushroom
bodies: in some of the flies with the mutation two vertical lobes are
missing, while others with the same mutation have two of the three horizontal
lobes missing. The team tested the memorization capacities of these different
mushroom body mutants.
The ala mutant flies have a perfectly normal short-term memory,
whether they lack the two horizontal lobes affected by the mutation, or
the two vertical lobes. This result suggests that short-term information
is located in the third horizontal lobe, the lobe that is not affected
by the mutation in the brain described in this work.
The long-term memory of flies lacking the two horizontal lobes is also
normal, although stable memory is abolished in the absence of vertical
lobes. A very small region of the brain is thus specifically involved
in long-term memory. This result is particularly interesting since the
vertical and horizontal lobes analyzed are formed with the same neurons,
which branch into two lobes. This means that there is a functional specialization
of the neuron projections of the mushroom bodies, as the vertical lobes
are the only location of long-term memory.
One of the interpretations suggested by the authors is that labile information,
which lasts several hours, and stable information, which lasts several
days, are stored in different neuronal pathways.
Reference:
Localization of long-term memory within the Drosophila mushroom
body. Pascual, A. and Préat, T. Science, November 2, 2001.
Researcher
contact:
Thomas Préat
"Génome, Mémoire et Développement" team,
"Développement, Evolution et Plasticité du Système
Nerveux" CNRS Laboratory
Tel: + 33 1 69 82 36 38
E-mail: preat@iaf.cnrs-gif.fr
Life Sciences
Department contact:
Marie-Pascale Corneloup
Tel: + 33 1 44 96 46 48
E-mail: marie.corneloup@cnrs-dir.fr
Press contac
:
Stéphanie Bia
Tel : +33 1 44 96 43 09
E-mail : stephanie.bia@cnrs-dir.fr
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