Escalated handling of young C57BL/6 mice results in altered Morris water maze performance

BACKGROUND: The handling of experimental animals prior to experimental interventions is often poorly described, even though it may affect the final functional outcome. This study explores how the use of repeated handling of C57BL/6 mice prior to Morris water maze (MWM) tests can affect the performance. METHODS AND MATERIALS: The handled animals were subjected to the escalating handling protocol, with the investigator spending 5 min per day per cage for 8 days prior to the MWM test. On the last days of handling, the mice were introduced to water and the concept of a hidden platform. The MWM test consisted of four daily trials for 90 s per day for 4 days with a hidden platform. A probe test was performed 4 days after the last learning trial. Control animals were not handled prior to MWM. RESULTS: Handling reduced the latency to find the platform on the first 2 days of the MWM tests and reduced thigmotaxis. The mice increased their swim speed and elicited more explorative behavior in the learning trials and to some lesser extent in the probe trials. CONCLUSIONS: The improvement in MWM navigation was most likely due to reduced stress and anxiety regarding the investigator and the test. Handled mice displayed less variability than non-handled mice, suggesting that by using a controlled handling protocol prior to the experiments fewer C57BL/6 mice would be needed to achieve statistically significant differences in studies of learning and spatial memory using MWM.