A study of the physiological psychology to investigate the brain mechanisms of the hyperactive and learning disorders using Tsukuba emotional strain rats as an animal model of these disorders.

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The present study was intended to clarify the brain mechanism of the hyperactivity and learning disorder, as well as to determine the appropriateness of Tsukuba low emotional strain (L strain) rats as an animal model of the hyperactive and learning disorder, by observing the general activity and various learning acquisition processes of these rats in detail. As a result, it revealed an interesting fact that the L strain rats showed a clear spatial learning disorder in the spatial learning problem with an 8-arm radial maze needing a working memory. In addition, peculiar circadian rhythm was observed in the L strain rats, and the validity of the hyperactive and learning disorder model of the L strain rats was confirmed. The morphological study mainly performed on the hippocampus which was important to spatial memory made very obvious that the volume ratio of the rostral part of the dorsal hippocampus for the whole hippocampus significantly decreased in the L strain rats, and that the volume ratio of the dentate gyrus for the dorsal hippocampus in these strain rats was quite lower compared with that in the other rats. Moreover, the findings displayed the negative correlation between the number of trials achieved in the spatial learning and the volume ratio of the dentate gyrus in the L strain rats. Therefore, the morphological transformation of the hippocampal dentate gyrus was suggested in terms of the spatial learning disorder.