Approximately 40-60% of BXSB/MpJ-Yaa mice exhibit neocortical ectopias, whi
ch are misplaced clusters of neurons in layer I of cortex. These ectopias a
re usually located in the prefrontal and/or motor region of cortex in BXSB
mice, and are similar in appearance to those found in postmortem analyses o
f the brains of dyslexic humans. Several within-strain learning differences
between mice with ectopias and those without have been reported. In partic
ular, ectopic BXSB mice exhibited superior reference memory learning, but i
nferior working memory learning in several studies from our laboratory. Thi
s study used the Morris water maze delayed matching-to sample task and the
water radial-arm maze to asses working memory in female BXSB mice with and
without ectopias. In the delayed matching-to sample task, a hidden escape p
latform remained in a constant position for each four-trial session, but ch
anged position between sessions. Trial 2 was the measure of working memory,
i.e., how well did the mouse remember where the platform was located for t
hat session. In the water version of the eight-arm radial maze, hidden esca
pe platforms were located in four of the eight arms, and each platform was
removed from the maze once found. This enabled us to assess working and ref
erence memory simultaneously. Ectopic mice demonstrated working memory defi
cits during the first part of the delayed matching-to sample task compared
to nonectopics. Similarly, ectopics made more working memory errors during
the latter half of radial-arm maze testing, while not differing from nonect
opics in reference memory performance. Additionally, there were significant
correlations between measures of working memory in the radial-arm maze and
working memory in a delayed matching-to-sample task. These findings are in
agreement with other studies demonstrating working memory deficits in ecto
pic BXSB mice. (C) 2000 Elsevier Science Inc. All rights reserved.