Long-term continuous, but not daily, environmental enrichment reduces spatial memory decline in aged male mice

• Published in: Neurobiology of learning and memory 2006-03, Vol.85 (2), p.139-152
• Main Authors: Bennett, Jennifer C., McRae, Paulette A., Levy, Lauren J., Frick, Karyn M.
• Format: Article
• Language: English
• Subjects: Aging; Aging - physiology; Aging - psychology; Animal; Animal ethology; Animals; Attention - physiology; Biological and medical sciences; Brain - metabolism; Escape Reaction - physiology; Exploratory Behavior - physiology; Fundamental and applied biological sciences. Psychology; Handling (Psychology); Hippocampus; Learning. Memory; Male; Mammalia; Maze Learning - physiology; Memory; Memory - physiology; Mice; Mice, Inbred C57BL; Neocortex; Orientation - physiology; Psychology. Psychoanalysis. Psychiatry; Psychology. Psychophysiology; Reference memory; Reference Values; Social Environment; Synaptophysin; Synaptophysin - metabolism; Vertebrata; Working memory
• ISSN: 1074-7427; 1095-9564
• DOI: 10.1016/j.nlm.2005.09.003

Although environmental enrichment improves spatial memory and alters synaptic plasticity in aged rodents, it is unclear whether all types of enrichment treatments yield similar benefits. The present study examined the effects in aged male mice of three types of enrichment on spatial memory in Morris water maze and radial arm maze tasks, and on levels of the presynaptic protein synaptophysin in several brain regions. Non-enriched young and aged males were compared with males exposed to one of the following treatments for 10 weeks: 5 min of daily handling, 3 h of daily basic enrichment, or 24 h of continuous complex enrichment. Young controls outperformed aged controls in both tasks. Neither daily handling nor daily enrichment affected spatial memory or synaptophysin levels. In contrast, continuous enrichment significantly reduced age-related spatial memory decline in both tasks, such that this group was statistically indistinguishable from young controls in most measures of performance. Continuously enriched mice were also significantly better than other aged mice in several spatial memory measures. Despite these improvements, synaptophysin levels in the continuous enrichment group were significantly lower than those of young and aged controls in the frontoparietal cortex, hippocampus, and striatum, suggesting a negative relationship between synaptophysin levels and spatial memory in aged males. These data demonstrate that different types of enrichment in aged male mice have disparate effects on spatial memory, and that the relationship between enrichment-induced changes in synaptophysin levels and spatial memory in aged males differs from that we have previously reported in aged female mice.