Circadian wheel-running activity rhythms are unaltered by acute cage enrichment with nests and shelters

C57BL/6J inbred male mice were assessed for the effects of cotton nesting material on circadian running-wheel assays at 60, 157 and 222 days of age. The oldest mice were also tested for effects of access to plastic igloo shelters and the combination of cotton plus igloos. All mice were assayed for mean activity level, acrophase and entrained circadian period in 12:12 LD, and mean activity level and free-running period in DD for circadian wheel-running activity. There were no significant effects, at any age, of either nesting material or shelters, or the combination of both, on any measures of circadian running-wheel activity. We conclude that circadian rhythm assessment is unlikely to be significantly altered by the inclusion of enrichment materials in running wheel cages.