The Journal of Neuroscience, October 15, 1998, 18(20):8534-8538
Decreased Odor Avoidance after Electric Shock in
Drosophila Mutants Biases Learning and Memory Tests
Thomas
Préat
Institut Alfred Fessard, Centre National de la Recherche
Scientifique, 91190 Gif-sur-Yvette, France
The Drosophila mutants amnesiac,
dunce (dnc), and rutabaga
were isolated after associative conditioning tests, during which animals were trained to associate the presence of an odor with that of
electric shocks (ES). In the absence of conditioning, the odor
avoidance (OA) of these mutants was shown to be normal, indicating that
their poor associative conditioning performance was attributable to
specific learning or memory deficits. However, I show that the
OA of the mutants is greatly decreased after their exposure to ES. This
effect can last for hours. These results strongly suggest that part of
the defect displayed by these mutants in associative conditioning tests
does not correspond to a learning or memory deficit but might arise
from abnormal sensitivity to stressful stimuli. I looked at the OA
after ES of two previously characterized dnc
mutants. Df(1)N79f specifically
decreases Dnc expression in the mushroom bodies, leading to a normal
level of learning but decreased memory.
Df(1)N79f mutants displayed a normal
OA after ES. Df(1)N64j15 affects the
entire brain expression of Dnc, leading to decreased learning and
memory. Df(1)N64j15 animals showed a
strong decrease of their OA after ES. Thus, the lack of Dnc
"general" expression is most likely responsible for the OA defect,
which would be responsible for the apparent learning defect after
conditioning. In contrast, the Dnc phosphodiesterase accumulated in the
mushroom bodies would be involved specifically in memory formation.
Key words:
Drosophila melanogaster; learning and memory
mutants; cAMP; stress sensitivity; odor avoidance; conditioning
controls
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