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Mutant mice that
express the R (AB) gene in the hippocampus, blocking the action of PKA, have
a selective defect for long-term contextual memory (A). Mice that express
R(AP) were conditioned to freeze to the context in the form of a box
illustrated in figure. The mice first walked around for a brief period of
time and became familiar with the context in which they walked. They then
heard a sound and received a shock delivered through the electrified grid in
the floor. As a result the animals learned to associate the context of the
space with shock and to freeze when placed in the box at a future time.
These mice learned well and had good short-term memory at one hour for
freezing to context. However, they no longer froze to context at 24 hours
after conditioning, indicating a defect in a form of long-term explicit
(declarative) memory that requires the hippocampus. Wild-type mice exposed
to anisomycin, an inhibitor of protein synthesis, during training show a
similar defect for long-term memory when tested 24 hours after conditioning
(B), indicating that the same phenotype is obtained with R (AB) mutation as
with inhibition of protein synthesis.
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