Influence of late-life exposure to environmental enrichment or exercise on hippocampal function and CA1 senescent physiology

Aged (20-22 months) male Fischer 344 rats were randomly assigned to sedentary (A-SED), environmentally-enriched (A-ENR), or exercise (A-EX) conditions. After 10-12 weeks of differential experience, the 3 groups of aged rats and young sedentary controls were tested for physical and cognitive function. Spatial discrimination learning and memory consolidation, tested on the water maze, were enhanced in environmentally-enriched compared with sedentary. A-EX exhibited improved and impaired performance on the cue and spatial task, respectively. Impaired spatial learning in A-EX was likely due to a bias in response selection associated with exercise training, as object recognition memory improved for A-EX rats. An examination of senescent hippocampal physiology revealed that enrichment and exercise reversed age-related changes in long-term depression (LTD) and long-term potentiation (LTP). Rats in the enrichment group exhibited an increase in cell excitability compared with the other 2 groups of aged animals. The results indicate that differential experience biased the selection of a spatial or a response strategy and factors common across the 2 conditions, such as increased hippocampal activity associated with locomotion, contribute to reversal of senescent synaptic plasticity.