Treatment of attention deficit hyperactivity disorder with medications is helpful in less than 60% of cases suggesting the necessity of development of novel drugs. The most accepted animal model of the disease is outbred spontaneously hypertensive rat strain. It was recently found in a novel enrichment discrimination test that the rat strain includes attentionally-low and -high phenotypes and clinically efficient drug for the treatment of the disorder atomoxetine is capable of ameliorating the enrichment discrimination by the attentionally-low rats. The present study aimed to test the generality of these findings in outbred CD-1 mice assessed in the same experimental design. The frequency distribution of the enrichment discrimination ratio differed from the curve expected under the normality hypothesis and had a bimodal shape suggesting the existence of attentionally-low and -high mouse phenotypes. Atomoxetine (3 mg/kg, orally, once daily for 4 days) selectively enhanced enrichment discrimination in mice of attentionally-low phenotype only. The present results generalize and extend findings previously reported in spontaneously hypertensive rats and suggest that the present model could be useful in studies of the neurobiological mechanisms of attention deficiency in rodents and for screening of novel drug candidates for treatment of attention deficit disorder.
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