Environmental enrichment and postnatal handling prevent spatial learning deficits in aged hypoemotional (Roman high-avoidance) and hyperemotional (Roman low-avoidance) rats.

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Abstract
The present study investigated the enduring effects of postnatal handling (administered during the first 21 days of life), and environmental enrichment (for a period of 6 months starting 3 weeks after weaning) on spatial learning in 24-month-old hypoemotional (Roman high-avoidance, RHA/Verh) and hyperemotional (Roman low-avoidance, RLA/Verh) rats. Two groups of 5-month-old rats from both lines were also included in the experiment as young controls. The Roman lines performed differently in the Morris water maze: Path lengths of RLA/Verh rats were shorter and they swam at lower speed than RHA/Verh rats, showing quicker and more efficient learning overall. Postnatal handling improved learning mainly in RHA/Verh rats, whereas environmental enrichment was able to prevent the deficits shown by aged controls of both lines. Young, enriched, and handled plus enriched animals exhibited better performance than impaired aged controls, to the point that aged enriched and handled plus enriched animals did not differ from young controls. Thus, besides indicating that RLA/Verh rats are better learners than RHA/Verh rats in the Morris water maze, this study demonstrates that environmental enrichment prevents the cognitive loss associated with aging, over the long term. Finally, the positive effects obtained with postnatal handling were dependent on the rat line.