Many injuries to the central and peripheral nerve systems, as well as, musculoskeletal disorders, have a direct link to motor system control and locomotion function damage. In animal models of these disorders, researchers have observed loss of: body balance, control and coordination resulting in motility issues. The most popular tool for assessing this type of damage has historically been the Rota-Rod apparatus; however, Columbus Instruments has recently developed the Foot Misplacement Apparatus to serve the same purpose.
The device consists of a set of two stainless steel horizontal ladders with different spacing between rungs to accommodate either rats or mice. A dark compartment is placed at one end of the ladder to entice the animal to walk toward the perceived safety of the dark cover. An electrical shock conditioning stimulus is used as negative reinforcement for training the animal upon touching the metal plate, which is located below the horizontal ladder. After the animal is conditioned, an actual test may be performed by placing the animal on one end of the ladder and counting the number of missteps as it moves toward the dark compartment at the other end.
Counting the animal’s missteps is done automatically via the detection of changes in resistance between the ladder and the metal plate. Each time the animal misses one of the rungs of the ladder and touches the metal plate below; a very small electric current is detected, amplified and counted by a separate computerized unit. The animal is unaware of this current, as it is far below the threshold of the animal's sensitivity. The apparatus comes with Columbus Instruments’ original software for digitizing and collecting the number of missteps and time passed in each trial; those data can then be imported to an Excel worksheet, which is very useful.
We are using this apparatus in our lab for investigating the re-innervating process following sciatic nerve crush surgery in rats. A trial is complete only when the rat runs over the ladder without changing its direction. The time cutoff for any trial was set up as the average time of the experimental group of animals (i.e. when they moved without stopping) and was previously determined. We tested the rats for 3 weeks on a daily basis, 5 days each week. Our observation has shown that the rat loses its memory of conditioning stimulation after about 7 days and we recommend the repetition of conditioning stimulation once each week. We have also installed additional walls on each side of the ladder, parallel to the moving direction, to prevent the distraction of the animal.
In conclusion, we believe that this new method can be very useful for the analysis of animal coordination change. It is less stressful than the Rota-Rod technique where the animal falls from the rotating wheel. However, Columbus Instruments should improve their software, making it more user-friendly. We have experienced problems with the ability to input notes regarding rat behavior during the experiment and the computerized test layout should be more customizable. Our overall impression is that we like the test system, counter and shocker, but we hope that the software will be upgraded.
Dmitriy Romanovsky Ph.D.
Postdoctoral fellow
Department of Anesthesiology
University of Arkansas for Medical Sciences