The influence of trait anxiety on performance in the CatWalk test.

Introduction: Trait anxiety refers to the individual variability in the predisposition to respond anxiously to stimuli. Anxiety has been shown to affect several physiological processes, including fine motor tasks, both in humans and in rodents. Therefore, trait anxiety may be a confounder factor in behavioral studies assessing motor functions in preclinical animal models. Among the tools employed to investigate motor functions in rodents, CatWalk XT is one of the most used. CatWalk XT is a computer-assisted apparatus that allows rapid and objective quantification of both static and dynamic gait parameters in rodents. The test consists of a training period in which the mouse learns to cross a platform and a test day in which the mouse footprints are recorded and analyzed. Methods: Here, we investigated whether trait anxiety, assessed with the Elevated Plus Maze (EPM) test, influences mice performance on CatWalk XT. Results: The results showed a correlation between anxiety levels as measured by the EPM and CatWalk test, with trait anxiety affecting the CatWalk learning and gait parameters. Indeed, mice with higher degrees of anxiety displayed a higher number of noncompliant runs during the training, ultimately protracting the time required by the experimenter to perform the CatWalk test. In addition, mice displaying fewer total entries in the EPM exhibited increased print lengths when assessed with the CatWalk system. Discussion: In conclusion, our findings indicate that individual differences in trait anxiety must be considered when testing mice with the CatWalk XT system. The use of specific anxiety tests before CatWalk testing may be useful to exclude those mice showing the highest levels of anxiety. This strategy would optimize researcher's time, limit animals' stress, and avoid errors in the results interpretation.