Enrichment-induced exercise to quantify the effect of different housing conditions: a tool to standardize enriched environment protocols.

Enriched environments (EE) have been used for a long time to promote recovery in many neurological disorders, however, a growing body of inconsistent results strongly calls for a rigorous standardization of experimental EE paradigms. Although some core principles are well accepted as standards, a method to quantitatively assess the complexity of EE in various experimental designs is still lacking. In this study, we tracked and recorded the physical exercise of rats in four housing conditions, namely isolated condition, social condition, novel condition and EE. Then, we analyzed whether and to what extent, enrichment-induced exercise reflected the degree of enrichment. We next examined rat exercise in a conventional environment condition and under different light intensities, to explore whether environment-related exercise could be considered a parameter to quantify the degree of enrichment. The results obtained showed that (1) both inanimate and social stimulations enhanced the exercise level and (2) EE combined the effects of the two stimulations. Furthermore, exercise durability which correlated positively with degree of enrichment, was an objective measure of different housing conditions. Exercise-related parameters also sensitively reflected the impacts of light intensity even in the same enrichment arrangements. Our results indicate that there is a direct and measurable correlation between degree of environmental enrichment and enrichment-induced exercise, and therefore enrichment-induced exercise could be used as a helpful tool to evaluate the degree of housing conditions and to standardize the EE protocols.