This method makes it possible to reproducibly quantify differences in gait parameters. The gait parameters can be assessed in freely-walking rodents, and the technique does not rely on invasive steps such as dipping the feet with ink. Demonstrating the procedure will be Ben Lamberty.
Begin by placing a home cage at the end of the walkway before the start of each run, to serve as a positive cue for the rat to traverse the walkway. Turn off the room lights. Power on the camera and start recording several seconds before the rat is placed on the platform.
With the enclosure installed, place the rat at the end of the walkway, opposite the home cage, and allow it to walk across the walkway in an unforced manner. Stop recording once the animal reaches the terminus of the walkway. Clean the walkway using 70%ethanol and a non-abrasive towel in between runs and after an animal urinates or defecates.
Then, allow ethanol to evaporate before introducing another animal. Run the rats through the walkway a total of seven times during each observation period, taking the first three runs that score as passing for analysis. Score a run as passing if the animal makes four or more consecutive steps in the direction of the home cage without interruption due to grooming, pausing, or errant movements.
Gait analysis was performed on male wild-type and Parkin DKO rats at two months of age to determine if the use of kinematic gait analysis could uncover subtle motor impairments prior to the appearance of gross motor problems. Despite the increased weight of the DKO rats, the foot pressure applied to the walking surface was unaltered. Upon assessment of several gait parameters as a function of walking speed, the walking speed and step lengths were found to be similar between wild-type and DKO rats.
The variation between wild-type and DKO rats became apparent in stance phase and swing duration at slower walking speeds. The fraction of the step cycle where the leg is in the stance phase was the duty factor. More time was spent in the swing phase than in the stance phase as the duty factor decreased.
Furthermore, while swing speeds increased with increased speed in wild-type animals, the correlation was blunted in DKO rats. The FTIR gait analysis was also used to create plots of stance phase traces of each leg relative to the body in freely-walking rats. Upon comparing the paw positioning, significant changes in AEP and PEP were observed.
Several additional parameters were significantly changed in the DKO rats as compared to wild-type. The swing speed of both the left and right hind limbs was increased in DKO rats, while the swing duration of both left and right hind limbs was decreased. Consistent setup of equipment, including camera position with relation to RatWalker, is important for the successful implementation of this protocol.
After performing this protocol, animals are available for any additional behavior or experimental endpoints necessary. For example, gait changes can be correlated with histological alterations. This technique can be used to assess gait in other non-PD rodent models, such as models of anxiety and depression.
