Enrichment Discrimination Behavior in Spontaneously Hypertensive Rats

Objectives: 1) To reveal, among spontaneously hypertensive rats, subpopulations that diverge in attention to objects enriching an empty cross-maze; 2) To evaluate effect of clinically efficient drug for treatment of attention deficiency atomoxetine on the attention to environmental cues in attentionally-low rats. Method: A novel paradigm that provides measure of attention towards enriching objects independent of general locomotor activity and spatial orientation is employed. The apparatus consists of 4-arm radial maze, two arms of which contain objects (enriched compartments). Animals exploring the objects typically stay longer in enriched parts of maze than in empty arms and have a higher score of enrichment discrimination ratio. Results: Frequency distribution of the enrichment discrimination ratio had clear bimodal shape that differed significantly from normal distribution suggesting the existence of subpopulations of attentionally-low and -high individuals. The attentionally-low phenotype did not show inferiority in spatial orientation as compared with attentionally-high phenotype. The phenotypes did not differ from each other in measures of locomotor activity and blood pressure. Atomoxetine (3 mg/kg, orally, once daily for 4 days) enhanced enrichment discrimination in animals of attentionally-low phenotype. Single administration of the drug was ineffective. Conclusion: Population of spontaneously hypertensive rat includes two phenotypes of attentionally-low and -high individuals. Subchronic atomoxetine ameliorates attention to environmental cues in attentionally-low rats. The enrichment discrimination test could be useful in studies of neurobiology of attention deficit condition and for screening of novel drug candidates.