Working memory deficits in BXSB mice with neocortical ectopias

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.