A neurobehavioral study of the attention-deficit/hyperactivity disorder (ADHD) model rat with an abnormal morphogenesis of the hippocampus or the cerebellum using

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We examined the correlation of the behavioral disorders with the morphogenetical abnormality of the brain in the attention-deficit/hyperactivity disorder (AD/HD) model animals which were induced by methylazoxymethanol (MAM) injection on the prenatal 15-day (MAM-15 group) or 19-day (MAM-19 group). Behavioral results were following, 1) the MAM-15 rat showed a hyperactive tendency and the MAM-19 rat showed a hypoactive tendency, which were measured by infra-red sensor during dark phase in a home-cage, during both weaning and adult periods, 2) the MAM-15 rat showed a retardation of the habituation to the environmental visual stimulus changing, and 3) the MAM-15 rat showed a severe impaired spatial cognition (especially spatial working-memory deficit) in the radial-maze and the Morris-type water maze learning situations, although the MAM-19 rat showed a moderate deficit, during both developmental stages. The behavioral disorder observed in the MAM-15 rat correlated with a morphological abnormality of the hippocampus (disruption of the CA1 pyramidal layer and ectopic neuron mass), and the behavioral disorder, although which were moderate, observed in the MAM-19 rat correlated with an abnormal foliation of the anterior cerebellum. Our behavioral and histological results suggest that the AD/HD-like behavioral disorder obtained in the present study may be derived from the brain dysfunction induced by abnormal morphogenesis of the hippocampus.