Candidate genes for learning and memory: microarray analysis of mouse hippocampi during acquisition of the Morris water maze task

The hippocampus is involved in learning and memory in rodents. This kind of neuronal plasticity is associated with de novo gene expression (GE). Thus, learning of a specific task will result in specific gene expression. Therefore, we trained mice in the hippocampus related Morris Water Maze (MWM) test and used microarray technology to determine gene-expression profiles in the hippocampus at several time points. We developed a cDNA microarray chip containing genes, involved in learning and memory. This gene chip allowed us to quantify mRNA expression in dissected hippocampi. C57Bl/6 x FVB mice were given four consecutive trials in the MWM. Mice were divided into three groups: complete control (CC, test naïve), swim learner (SL, learning animals) and the swim controls (SC, without platform–motion and affective controls). Thus, the microarray assay SC/CC provided differences according to stress/motion-related GE and the SL/SC comparison the exclusively learning effect of GE. Samples of CC, SC and SL were prepared 1hr, 6hrs and 24hrs after training and hybridized to the gene chip. Although 4 trials were not sufficient to improve behaviour, SL/SC (n=5) comparison revealed 5 genes regulated, however, less than the SC/CC comparison (n=16, e.g. Mapk8ip, Kcnma3, Kcnq1). For both, down regulation (↓25 vs. ↑3) was more prominent on criterion of 1.5 fold. Timm22 and Syt5 were downregulated in both assays. However, learning dependent regulation occurred only after 6 hrs and 24 hrs.