Optimization of overhead enclosure monitoring in juvenile male Dunkin Hartley guinea pigs (

Overhead enclosure monitoring provides objective quantitative mobility measurements for animals undergoing open-field testing. Notably, protocols for testing optimization have been minimally established for the guinea pig. It is unknown whether (a) repeated exposure, (b) time-of-day, or (c) length of testing duration influence outcome parameters. We hypothesized that guinea pigs would display decreased activity following repeated exposure to the open field; heightened activity during the earliest testing period; and that 10 min would be adequate for data collection. The study was conducted in two separate phases to distinguish between enclosure habituation and time-of-day effects, respectively. Two cohorts of male Dunkin Hartley guinea pigs were allowed voluntary movement in an open-field enclosure for 14 min to quantify mobility outcomes, including total distance traveled, total time mobile, average speed while mobile, and total time spent in the shelter. For both phases, testing occurred at four different times of day, and overhead monitoring software was programmed to divide the total testing duration into 2-min bins. Habituation phase results showed time mobile and distance traveled were influenced significantly by repeat exposure, as animals were most active during the first testing event. Time-of-day phase animals spent significantly more time mobile during the earliest testing period. Interestingly, significant differences were observed across 2-min bins for the time-of-day phase but not during the habituation phase. Specifically, progressively decreased ambulatory activity was observed as testing duration increased. Thus, habituation and time-of-day should be accounted for when possible. Finally, a trial period greater than 10 min may not yield additional data.