Physiological effects of environmental enrichment on BALB/c and C57BL/6 strain mice

Our aim was to assess the effects of enriched environment (EE) on some physiological variables, comparing BALB/c and C57BL/6 strain mice. Female BALB/c and C57BL/6 were individually housed under standard laboratory cages for 6 weeks and randomly separated into groups (n = 7 per strain per group): Standard environment (SE); Environmental enrichment (EE). The EE protocol consisted of toys and nesting material in home cages for each mouse. Weight gain, systolic blood pressure (SBP), heart rate, and gastrointestinal transit were assessed in SE and EE groups after 6 weeks. At sacrifice, corticosterone serum, thymus and splenic weight, and intestinal histology were also determined. There was no significant difference in body weight gain or heart rate; however, EE significantly reduced the plasma levels of corticosterone and SBP compared to SE groups in BALB/c and C57BL/6. Gastrointestinal transit was faster in BALB/c mice compared to C57BL/6 mice in SE. EE did not significantly change the transit for BALB/c mice, but was markedly accelerated in C57BL/6 mice. There was no difference in the thymus/body weight ratio for strain or housing condition; however, BALB/c mice displayed a higher spleen/body weight ratio compared to C57BL/6 regardless of housing conditions. Our data reinforce the importance of choosing the better experimental model due to the difference between the strains and importance of including EE, especially for the C57BL/6 strain, where there seems to be more physiological impact.