Barnes maze test revealed spatial learning and memory deficits (for long-term assessment) in C57BL/6J male mice following primary blast brain injury

STUDY PURPOSE: This Barnes maze test measured the abnormal learning pattern and long-term memory deficits following primary blast brain injury. DATA COLLECTED: A total of 25 male C57Bl/6J mice, 2 months old, were used in the Barnes Maze studies, described by Song et al. 2018 [PMID: 29526786]. The animals were randomly grouped and blinded to investigators who carried out the experimental analyses. Mice exposed to open-field blast (OFB) in the 3-m and sham control groups were tested at 22-29 days post-injury (DPI) (n=13 for 3-m blast and n=12 for sham), respectively. Sham group underwent the identical procedures only without blast exposure. Mice were placed in the prone position on platforms located 3 meters away from the 350 g of C4 explosive (both positioned 1 m above ground). No restraint was applied to the animals. After blast exposure, mice were tested for behavior assessments. Mice were socialized with the investigators for 7 days prior to the start of behavioral testing. Mice were transferred to the testing room and acclimated for at least 30 min prior to the start of testing. Barnes maze test (n=25; 3-m blast group, n=13 and sham group, n=12) was performed to assess spatial learning and memory. The maze consists of a circular platform (75 cm in diameter) with 20 holes (5 cm in diameter) evenly spaced around the platform’s perimeter; it is elevated 56.5 cm above the floor by a stand. For each mouse, one hole was assigned as the escape hole, and an escape box was located beneath the hole. The escape box location remained constant for any individual mouse across test trials. Three 100-W lights were hung on the ceiling above the platform to create a potentially adverse environment. Brightness was measured at the center and corners of the four quadrants of the apparatus and maintained at approximately 3000 lumens throughout the surfaces of the platform in order to motivate the mice to escape from the brightly lit open surface to the more favorable darker environment of the box. Four shapes – plus, square, triangle, circle - in solid black color printed on A4 copy paper were used as the visual cues. Each shape was placed at one quadrant side of black curtain. It remained at the same location for the test. Behavioral testing consisted of 2 habituation trials on the first day (shaping day) and 8 evaluation trials (2 trials/day) over the next 4 days, called acquisition days. Reversal training consisted of 2 trials per day for 3 days, with an inter-trial interval of 20-30 min and began 24 h after the last acquisition trial. Prior to the start of reversal training, each mouse was assigned a new escape hole, which is on the opposite side of the maze from the previously assigned hole. All the mice from both groups performed all 16 trials (maximum trial number) within 5-min duration for testing. Latency (time it took for the mouse to find the escape box) and total errors (nose-pokes into non-escape holes) were recorded. The duration of latency time needed to locate the escape hole was considered as primary latency, and the duration of latency time needed to fully enter (75% of the mouse’s body) into the escape hole was considered as total latency. Errors were defined as the number of mice investigated any hole other than the escaping hole in all four quadrants. The number of incorrect holes checked prior to locating escaping hole was considered as primary errors. Total errors include the number of all the incorrect holes investigated by mice before fully entering the escape hole. In the ANY-maze program, an “investigation zone” (defined as 15 mm around each hole) was set. The errors were automatically scored by the ANY-maze program when animal’s head moved towards the holes and poked within the 15 mm distance around the holes, or into the holes to investigate. The head tracking feature of ANY-maze (Use the position of the animal’s head) was used for tracking the mice. All the parameters were subsequently scored and analyzed by ANY-maze (v.4.72, Stoelting Co., Wood Dale, IL; Windows XP OS). DATA USAGE NOTES: