Open-field behavior is not related to treadmill performance in exercising rats

Abstract We examined the association between open-field behavior and treadmill performance in 39 adult male Sprague-Dawley rats. Three daily, five-minute trials were conducted in an open field of 49 19 cm squares. The objectivity of the open-field test was established by intraclass correlations (R) for observer agreement on total squares traversed (R=.99) and a subjective behavioral rating scale for anxiety (R=.92). As expected, total squares were inversely correlated (r=−.86) with the subjective anxiety ratings. An independent observer also rated animals on treadmill performance across six daily, five-minute trials of level running at 15 m/min. Performance ratings were objective (r s =.89) and reproducible (R=.91). A volitional endurance run at 30 m/min on level grade was also conducted on a subsequent day. Extreme groups of low anxious (N=7) and high anxious (N=7) animals were then identified from convergent responses on total square traversals and the subjective behavioral ratings that were reproducible (R=.72 to .78) of trials two and three of the open-field test. Repeated measures ANOVA showed no group differences ( p >0.10) on mean treadmill performance across trials. Endurance was also the same for each group ( p >0.05). Our findings indicate that the open-field test is objective and reliable, and it does not reveal a selection bias effect on treadmill performance or endurance. Thus, open-field behavior can be used as a dependent or subject-matching variable in studies of adult male Sprague-Dawley rats when motor-driven treadmill running is a behavioral intervention or outcome measure.