Barnes Maze

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Materials and Methods
Mice were singly housed on sawdust in standard Makrolon type II cages enriched with cardboard nesting material for at least one week prior to experiments, with water and food ad libitum (7:00/19:00 lights on/off; providing an abrupt phase transition).

Associated Mammalian Phenotype Ontologies (MGI)
- MP:0001392 abnormal locomotor behaviour
- MP:0002063 abnormal learning/memory/conditioning

Barnes maze
Apparatus and room: The Barnes maze consisted of a circular grey platform (diameter 120 cm) elevated 100 cm above the floor with 24 holes (4.5 cm diameter) spaced at equal distance 5 cm away from the edge of the platform. One hole was designated as escape hole, and equipped with a cylindrical entrance (4.5 cm diameter x 5 cm depth) mounted underneath the maze providing access to an escape box (15.3 x 6.4 x 6.1 cm) containing a metal stairway for easy access that was not visible unless mice approached the hole closely. Other holes were equipped identical cylindrical entrances, but without escape box. Visual extra-maze cues (50 x 50 cm) composed of black and white patterns were mounted on the walls ~70 cm away from the maze. Three fans surrounding the maze (60 cm away from the maze spaced ~120° apart) produced a variable airflow across the entire maze by a slow 90° horizontal movement, proving both an aversive environment as well as dispersion of any odor cues. Several fluorescent tube lights mounted at the ceiling provided bright illumination (1000 lx). A speaker mounted to the ceiling provided background sound.
Protocol: Mice received training sessions twice a day, typically in the morning and afternoon. Mice were introduced in an opaque cylinder (x cm diameter, x cm high) placed in the center of the maze, after which the experimenter left the room and closed the door. The cylinder was pulled upwards 30 s later, and mice could explore the maze to locate the escape hole. If the latency to enter the escape hole exceeded 300 s, mice were gently guided toward the escape hole. During the first 2 habituation sessions, the escape box contained cage enrichment of a mouse's own home cage, and once in the cylinder, mice were left in there for 60 s. After each mouse, the platform and escape box were thoroughly cleaned with 70 % ethanol. The platform was rotated 90° after each trial to avoid the use of any odors cue. During a 300 s probe trial the escape hole was identical to all 23 other holes.
Data analysis: The path travelled by a mouse was video tracked by an overhead camera and analyzed using Viewer 2 software with Barnes maze plugin (BIOBSERVE GmbH, Bonn, Germany). The distance and latency to reach the target location were recorded, as well as hole visits defined by crossing of the head reference point into a hole zone drawn 1 cm around each hole. Multiple consecutive hole visits were counted as single hole visit, and the number of single hole visits to holes other that the target hole were counted as errors. Mice may develop a serial search strategy to locate a target hole. A hole visits was marked as serial visit, if the previous visit has occurred 1 or 2 holes away. As index of a serial search strategy the percentage of serial hole visits was calculated as follows: (total hole visits) / (serial hole visits). To detect a spatial search strategy, the Barnes maze was divided into octants, and the target zone comprised the escape hole and the hole immediately to the left and right of the escape hole. The proportion of hole visits to the target zone was calculated as follows: (total number of visits to a hole in the target zone) / (total number of hole visits). This proportion was calculated per bin of 10 hole visists, as well as for the entire trial.

Parameter information
Parameter nameUnits
*Escape latency (s) per day (5 days)Latency
*Distance to target hole (cm) per day (5 days)cm
Hole visits in target octant (probability) per day (5 days)Probability
Errors per day (5 days)Errors
*Probe trial: hole visits in target octant (probability)Probability
Escape latency on day 5seconds
Number of errors on day 5Frequency
Distance to target hole on day 5cm
Probe trial: total number of errorsTotal errors
Serial errors (proportion of total errors) per day (5 days)Serial errors per day
Hole visits in target octant, first block of 5 visits (probability) per day (5 days)Probability
Escape latency - first dayLatency