Versamax animal activity monitoring system

Locomotor activity was quantified in an open field chamber equipped with a Versamax Animal Activity Monitoring System (AccuScan Instruments Inc., Columbus, OH) under normal laboratory light (~770 lux). Following acclimation, mice were individually placed into the center of the open field and allowed to explore the chamber for 1 hr once the experimenter left the room. Total distance traveled and time spent moving were calculated for the 42 L × 42 W × 20 H cm chamber. Anxiety-like behavior was evaluated by quantifying the percentage of time spent in the center zone of the open field arena over the 1 hr testing period. The center zone was defined as a square comprising 40% of the arena. As open field activity is largely driven by exploratory behavior of a novel environment¹⁵ , mice were only tested in the open field once. Thus, open field activity across multiple post-CFA timepoints was acquired from separate cohorts of mice.

On PD 16, pups were separated from the dams and placed in pairs in holding chambers for 1 h. Locomotor activity was then evaluated for 5 min in a testing environment that consisted of an open-field chamber with Plexiglas^® walls (42 × 42 × 30 cm; VersaMax Animal Activity Monitoring System, Accuscan Instruments; Columbus, OH). The chambers were equipped with a light which could be turned on or off (intensity: 0 or 50 lux). Locomotion was detected by interruption of eight pairs of intersecting photocell beams evenly spaced along the walls of the testing environment. This equipment was situated in sound-attenuating chambers (53 × 58 × 43 cm) equipped with a fan for ventilation and background noise. Consecutive photocell beam interruptions were translated to distance traveled in cm by the VersaMax software. This dependent variable takes into account the path of the animal and is an accurate indicator of ambulatory activity. Immediately after the locomotor activity, test pups were returned to their home cage. Prior to this evaluation of locomotor behavior, animals were intubated with ethanol at 0.0, 0.5, or 2.0 g/kg; a fourth group was not intubated. Five minutes after ethanol administration, animals were tested in the chambers with the light turned on or off.

Rats were challenged with amphetamine to examine dopamine-mediated hyperlocomotor activity and to determine whether levetiracetam treatment would alleviate the increased response to amphetamine that is characteristic of the ketamine model. Using a within-subject design, each rat was treated with either levetiracetam or saline on different test sessions; the order of drug treatment was counterbalanced such that half of the rats received levetiracetam on the first test session and saline on the second one, and vice versa. The test sessions were separated by at least one day of drug washout. During the test, each rat was injected intraperitoneally with levetiracetam (10 mg/kg) or saline and placed in an open field chamber (42 cm × 42 cm × 30.5 cm) in which locomotion was tracked with the VersaMax animal activity monitoring system (AccuScan Instruments, Columbus, OH). After 30 min of baseline activity, the rat was taken out of the chamber and injected intraperitoneally with a small dose of amphetamine (0.5 mg/kg in a volume of 1 ml/kg; Sigma, Saint Louis, MO). The rat was then returned to the chamber for another 60 min of activity monitoring. Total distance travelled and movement time were the dependent measures.