A Metric Test for Assessing Spatial Working Memory in Adult Rats Following Traumatic Brain Injury

Traumatic brain injury is commonly associated with memory impairment. Here, we present a protocol to assess spacial working memory after traumatic brain injury, via a metric task. The main advantages of metric tasks include the possibility of dynamic observation, low-cost reproducibility, relative ease of implementation, and low stress environment.

To evaluate the neurological severity score after parasagittal fluid percussion injury, place the adult Sprague Dawley rat at the center of a 50 centimeter diameter circle, three times and monitor its ability to exit the circle. To test for a loss of righting reflex, place the animal on its back in the palm of the hand and give a score of one if the rat is able to right itself. To test for hemiplegia, evaluate the inability of the rat to resist forced positioning.

To test the reflexive bending of the hind limb, raise the animal by its tail. To test the ability to walk straight, place the rat onto the floor. To test the pinna reflex, perform light, tactile stimulation to observe the ear retraction.

To test the corneal reflex, lightly apply a soft stick to the eye and measure the blink response. To test the startle reflex, drag a pen across the top of the wire cage and record the animal's response. To grade the loss of seeking behavior in prostration, place the rat into a new environment and observe whether the rat moves its whiskers, sniffs, or runs.

Then test the limb reflexes for placement on the left and right forelimbs followed by the left and right hind limbs. To test balance, perform a beam balancing task by placing the rat onto a 1.5 centimeter wide beam, for one 20, 40 and greater than second session. Then run a beam walking test using three beams of different widths.

Before performing the metric task, place a 200 centimeter diameter, one centimeter thick, black circular platform onto an 80 centimeter tall table and place two objects in the center of the platform, 68 centimeters apart. Install a camera with the required computer software for capturing, saving, and processing data, at a height of 290 centimeters from the floor. One day before the analysis place the rat on the platform for 10 minutes to habituate the animal to the new environment.

On the day of the task, place the rat on the end of the platform, equidistant from the objects for a 15 minute habituation period and start recording. At the end of the experimental habituation period, transfer the rat to an individual cage for five minutes and clean the platform with five to ten percent alcohol. Reduce the distance between the objects to 34 centimeters, then place the rat on the platform for five minutes while recording its exploration activity.

Clean the platform again, before proceeding with the next animal. Prior to analyzing the video files, insert the software hardware key, then start the video tracking software and open the preset template. After verifying, duplicating, and renaming the arena trial control and detection settings in the main field of view, right click the mouse to select grab background.

In the browse menu select the location of the video file to be used as the background image. Capture the image and mark the investigated areas and zones to calibrate the image for analysis. Perform the same setup for the trial control and detection settings.

After downloading the list of video files for analysis from the trial list, add the videos and indicate the location with the required settings. Then select acquisition and start trial and export all data into a spreadsheet. The control group does not show any neurological deficits, 48 hours after the sham injury.

After TBI, neurological deficits are significantly greater in both male and female injured animals. During the metric task, the object exploration time is significantly shorter for the male TBI rats than for the male sham operated rats. The same pattern is observed for the female TBI and female sham operated rats.

Following the metric task, we can perform other methods for memory assessment, such as the Barnes maze and topological and water maze tasks. The metric task also allows for further research into memory impairment in comparable models of neurological damage, such as models of diffuse axonal brain injury and stroke.