Assessing Spatial Memory Impairment in a Mouse Model of Traumatic Brain Injury Using a Radial Water Tread Maze

The overall goal of this Radial Water Tread Maze protocol is to test spatial memory in a mouse model of traumatic brain injury using a mouse centric cognitive task that does not require swimming. This method can be especially useful for testing cognition in mouse models, where motor deficits and or a lack of motivation makes swimming based cognitive testing protocols such as the Morris Water Maze impractical. Though this method could provide insight into group differences and cognition in a controlled cortical impact model of traumatic brain injury in mice, it can also be useful for measuring cognition in aged, and transgenic mouse models that are known to perform poorly in swimming based tests.

On all testing days, perform the following preparatory steps. First, allow the mice to acclimate to the test room, while in their home cages for at least 30 minutes. The round maze features visual cues along the inner walls.

The movable escape box positioned at one of nine different exit holes. While the mice acclimate, sanitize the exits and the box using a 70%ethanol spray. Next, fill the maze with roughly one inch of cold water.

Keeping the water temperature consistent between trials is very important. So measure accurately, and adjust as needed. Now, position the escape box at one of the nine exit holes.

Using a heating source to keep the box warm, ideally using a heating pad. Also, seal the box from light. The escape box should always be dark, warm and relatively odorless.

The light source is also likely to be a cue so do not change its position between trials. Remove the test mouse from its cage gently by the tail, and place it in the center of the apparatus. Then immediately start timing how long it takes for the mouse to find the exit.

If a mouse climbs into a terminating hole, and does not spontaneously reenter the maze after 20 seconds, do not stop the trial. Instead, guide the mouse back into the center of the maze by hand, and let the mouse complete the trial. If after three minutes, the mouse hasn't exited the maze, score the trial as a failure, and record the time as three minutes.

Then by hand, carefully guide the animal along the straightest path to the exit. Once in the escape box, allow the mouse to remain there for one minute. Then transfer it back to its home cage while the maze gets reset.

Between trials, thoroughly sanitize the escape box and exits with a 70%ethanol spray to prevent the mouse from using old factory cues to locate the correct escape route. This can be done pretty quickly. Now, repeat the trial on the same mouse twice more for a total of three consecutive trials.

Every testing day consists of three trials per mouse. No more, and no less. In addition to sanitizing, drain the maze and refresh the water between testing different mice.

Be sure to keep the water temperature between 12 and 14 degrees Celsius. Use containers of ice or colder hot water to adjust the tap water temperature into this range. Between testing days, it is important to make certain that the visual cues in the maze, and in the space surrounding the maze remain consistent.

A complete testing regime includes five consecutive testing days all run in the same manner. The fifth day is considered the measure for memory retention. Provided no tests are performed between day six and 11, a test on day 12 can be used to measure long term memory.

The radial water maze was used to investigate injury dependence spatial memory deficits in mice receiving either controlled cortical impact induced traumatic brain injury or a sham injury. The TBI surgery is described in detail in the text protocol and in a JoVE article by Romin, Gao and Chen from 2014. Briefly put, the injury was generated using a solenoid driven cortical impact with a three millimeter convex tip.

The shams were operated on but impacted by the device. 35 days post surgery, the described testing regime was performed. All the mice passed the criteria test for a desire to escape the maze.

So all were included in the analysis. The results show a clear difference between the TBI mice and sham controls. Escape latency was significantly longer for injured mice on the first day of training, and on both of the two memory test days.

Thus, the described TBI affected the animal's capacity to learn. After watching this video, you should have a good understanding of how to properly perform cognition testing using a mouse specific test of spatial cognition. Once mastered, this technique can be done in less than 15 minutes per animal if it is performed properly.

While attempting this procedure, it is important to remember that the positioning of visual cues and the water temperature must remain consistent across all trials.