Speed and Agility in Rat Gait Dynamics

Abstract

Rats are commonly used to study many diseases that affect mobility, including spinal cord injury, stroke, and arthritis. Inadequate neurological scales, however, have hampered functional assessment of motor function. Analyses of paw print walking tracks, for example, do not provide data regarding gait kinetics and do not take into account differences in the subjects' walking speeds. Especially as many CNS and neurodegenerative diseases affect gait posture and kinetics, spatial and temporal features of gait are most useful for assessment of sensorimotor performance. We developed, therefore, an automated assay for characterizing gait dynamics in rats. Here we demonstrate which gait dynamics are modulated by rats to increase walking speed by 50%.

Methods Rat gait dynamics were monitored using The DigiGaitTM Imaging System, as described previously¹ Briefly, DigiGaitTM incorporates high-speed videography to image the underside of rodents walking on a motorized transparent treadmill belt. Training to walk on the treadmill was not required. Baseline recordings were performed while walking at a speed of 36 cm/s for 3 seconds. The treadmill speed was then increased 50% to 54 cm/s. Imaging of the ambulating rat was immediately repeated for 3 seconds. DigiGaitTM analyses software calculated spatial and temporal indices of gait based on the advance and retreat of paws relative to the treadmill belt and video camera (Figure 1). Figure 1.

Results

Figure 2.

Discussion

Gait dynamics in rat were significantly altered by a 50% increase in walking speed. The step pattern observed at both walking speeds was “alternate”, with forelimb and diagonal hind limb footfalls occurring in sequence and nearly simultaneously. The increase in speed was accomplished predominantly by a ~33% increase in step frequency and a ~12% increase in stride length. Stride duration and stance duration were significantly decreased at the faster walking speed, but swing time was unchanged. Data collected via DigiGait are comparable to those reported by others measured via less automated methods.^2-4 In healthy rat, braking duration is longer in forelimbs than in hind limbs, and propulsion duration is longer in hind limbs than in forelimbs, similar to what we have demonstrated in mice.¹

Functional scoring is important in the testing of new compounds, yet many of the simple neurological scales provide conflicting results. There is a recognized need for refined tests for evaluating gait and neuroprotection in rat models of stroke.⁵ Advantages to our ventral plane videography method include not only measurement of spatial and postural indices, including stance width, stride length, and paw placement angles, but also determination of dynamic temporal indices, including braking and propulsion components, relative contributions of stance and swing, and stride length variability. We observed, for example that stride length variability and stance width variability decreased with increases in walking speed.

To what extent gait indices and interlimb coordination are affected by pathological conditions remains to be determined. Dynamic analyses of gait in rats will accelerate understanding and treatment of pathologies that affect coordinated locomotion, including stroke, spinal cord injury, arthritis, and pain.

References

1: Hampton, T.G. et al. 2004. Physiol. and Behav., in press.
2: Gorska, T. et al. 1999. Acta. Neurobiol. Exp. (Wars.) 59:131-144.
3: Hruska, R.E. et al. 1979. Life Sciences 25:171-180.
4: Clarke, K.A. and A.J. Parker. 1986. Physiol. and Behav. 38:345-351.
5: Reglodi, D. et al. 2003. Brain Res. Bull. 59:459-466.