Spinal Cord Awareness Day, September 21, 2010, is a collaboration of Massachusetts rehabilitation facilities, consumer organizations, legislators, policy makers and advocates working toward a common goal to increase funding available for spinal cord injury research in Massachusetts.
The purpose of Spinal Cord Awareness Day is to inform and remind legislators, the media and the public of their presence, the position of their research, leadership, and the economic and humanitarian benefits of funding for a cure.
Mouse Specifics, Inc., a Massachusetts company, takes great pride in its DigiGait Imaging System for providing quantitative evidence of spinal cord injury, and restoration of function with potential therapies, in animal models. DigiGait is in use in Massachusetts, in the United States, and worldwide to better understand and develop therapies for numerous human conditions, including amyotrophic lateral sclerosis, muscular dystrophy, and arthritis, in addition to its application to SCI research, some of which is described below.
Abstract
The most devastating effect of spinal cord injury [SCI] is the loss of the ability to walk. Animal models of SCI are critical to the development of therapies to restore locomotive capacity. Based on various animal models, it is generally accepted that central pattern generators (CPG) exists for the rhythmic generation of stepping movements. Computerized gait analysis is becoming increasingly important to the SCI research community, to provide quantitative metrics broadcast by the CPG. DigiGait™ uses ventral plane videography to provide two-dimensional and three-dimensional gait analysis in rodents, reporting metrics that reflect the numerous postural and kinematic aspects of rhythmic stepping.
Methods
Gait dynamics in animal models of spinal cord injury can be performed with The DigiGait Imaging system. The most important confounder in the interpretation of gait data are differences in walking speeds between healthy sham control animals and animals with SCI. Overground gait analysis, therefore, often provides inconclusive data because of the usual slower walking speed in injured animals. Injured animals will often prefer not to walk, or may walk slowly, and therefore many of the gait metrics, such as reduced stride length, are secondary to a slower walking speed. DigiGait empowers the investigator to have all animals walk the same speed, or a range of speeds [0.1 cm/s to 99.9 cm/s]. Quantifiable differences, such as more open paw placement angle or reduced duty cycle, can then be attributed to a gait disturbance rather than a slower walking speed. Typical treadmill walking speeds for rat models are in the range of 20-40 cm/s. Typical treadmill walking speeds for mouse models are in the range of 15-60 cm/s. The speeds achievable are often dependent on strain, age, and disease model. Protocols are model dependent, and can include challenging the animals with uphill and downhill walking and running.
Results
Even animals with complete transection of the spinal cord are able to perform the walking test on the DigiGait treadmill. Figure 1 illustrates a rat with transection of the spinal cord walking 20 cm/s, the same speed as its sham controls. Despite the loss of hind limb function, the forelimbs operated more frequently to maintain the animal’s speed. Forepaw and forelimb postural adjustments were also apparent.
Figure 1: Ventral view video of spinal injured rat treadmill walking 20 cm/s. Note the splay of the forepaws and widened forelimb stance width.
Figure 2. Dynamic gait signals generated by the DigiGait™ system, indicating stepping characteristics of forelimbs (upper) and hind limbs (lower) of a rat recovering from SCI. Note the qualitative differences in a forelimb gait signal compared to a hind limb gait signal [e.g., sharp upstroke during the braking phase in the hind limbs].
As spinal injured animals recover, hind limb stepping is gradually restored, but with a marked asymmetry in the forelimb and hind limb stepping frequency. Note in Figure 2, for example, the increased stepping frequency of the forelimbs vs. the hind limbs in a rat recovering from SCI. The Basso-Beattie-Bresnahan (BBB) score for this rat was 14. Gait symmetry, which is the ratio of forelimb-to-hind limb stepping, was ~1.4 for this rat. [Note: in normal animals, and in animals with a BBB score of 21, gait symmetry is ~1.0.] Phase dispersion, a metric introduced by Michelle Basso’s laboratory [1] provides a quantitative metric of coordination. DigiGait adopts the published mathematical algorithm, which was applied to several rats walking overground at indeterminate speeds, and applies it to any animal walking any speed. Below is a summary of coordination values for a rat with SCI and a sham control rat.
Diagonal RF LH(%)
Diagonal LF RH(%)
Girdle LF RF(%)
Girdle LH RH (%)
Ipsilateral RF RH(%)
Ipsilateral LF LH(%)
SHAM
13.2
14.5
51
50.5
64.8
64.7
SCI
21.1
25.4
47.7
29.9
40.9
27.8
Discussion
Correct assessment of forelimb and hind limb coordination during walking is one limitation within the BBB locomotor rating scale to quantify locomotor recovery following spinal cord injury [2]. Analysis of overground walking, moreover, is significantly confounded by differences in walking speeds among and between treatment groups of animals [3]. Ventral plane videography using the patented DigiGait™ imaging treadmill provides accurate assessment of coordination and robust gait kinematics at comparable walking speeds [4]. DigiGait™ reports over 30 metrics of posture and locomotion, many of them developed specifically for spinal cord injury research. Gait symmetry, phase dispersion, paw area variability, and weight support provide quantitative indices reflective of loss of coordination, dorsal stepping, and weight bearing. DigiGait™ also reports external and internal rotations of the paws, step sequence pattern, and nerve functional indices, including the sciatic, peroneal, and tibial functional indices (SFI, PFI, & TFI). Quantitative and controlled assessment of gait indices should facilitate testing of new drugs to restore locomotor function following spinal cord injury. To date, DigiGait has investigated transgenic inhibition of Nogo-66 receptor function [3], chondroitinase [5], and NMDA receptor-mediated excitotoxicity plus oxidative stress, as potential therapies for spinal injury [6].
References
1. Stepwise motor and all-or-none sensory recovery is associated with nonlinear sparing after incremental spinal cord injury in rats. Exp Neurol. 2005;191:251-65.
2. The assessment of locomotor function in spinal cord injured rats: the importance of objective analysis of coordination. J Neurotrauma. 2005; 22:214-225.
3. Transgenic inhibition of Nogo-66 receptor function allows axonal sprouting and improved locomotion after spinal injury. Mol Cell Neurosci. 2005;29:26-39.
4. Quantification of locomotor recovery following spinal cord injury contusion in adult rats. J Neurotrauma. 2006; 23:1632-1653.
5. Effects of acute chondroitinase treatment and training on functional recovery following moderate spinal cord injury in rats. Program No. 405.6/TT10. Neuroscience Meeting Planner. San Diego, CA: Society for Neuroscience, 2007; online.
6. The functional and neuroprotective actions of Neu2000, a dual-acting pharmacological agent, in the treatment of acute spinal cord injury. J Neurotrauma. 2010;27:139-49.
Figure 2. Dynamic gait signals generated by the DigiGait™ system, indicating stepping characteristics of forelimbs (upper) and hind limbs (lower) of a rat recovering from SCI. Note the qualitative differences in a forelimb gait signal compared to a hind limb gait signal [e.g., sharp upstroke during the braking phase in the hind limbs].