X-Ray Fluoroscopy-Based Kinematic Analysis of Quadrupedal Locomotion in Slow and Fast Fatigue-Resistant Motor Neuron-Deleted Mice.

Introduction/aims: VAChT-Cre is a transgenic mouse line targeting slow-twitch fatigue-resistant and fast-twitch fatigue-resistant motor neurons that innervate oxidative type I and type IIa muscle fibers. To ablate these neurons, VAChT-Cre mice were crossbred with NSE-DTA mice, leading to the expression of diphtheria toxin A after Cre-mediated excision. The resulting VAChT-Cre;NSE-DTA mice exhibited motor deficits, abnormal locomotion, muscular atrophy, and tremor, making them a useful model for studying motor neuron physiology and pathology. In this study, we conducted a kinematic analysis to examine their abnormal locomotor phenotype.

Methods: The quadrupedal walking of VAChT-Cre;NSE-DTA and control mice along a 500 mm acrylic tunnel was analyzed using an X-ray fluoroscopic system. Stride duration, stride length, footfall patterns, and limb and trunk kinematics were quantified and compared between the two groups.

Results: Our results demonstrated that VAChT-Cre;NSE-DTA mice walked more slowly than control mice (99.2 ± 43.5 mm/s vs. 120.5 ± 27.0 mm/s) and had a longer cycle duration (0.54 ± 0.19 s vs. 0.41 ± 0.09 s). In addition, the hindlimb was comparatively more flexed during the stance phase, the trunk was more rounded and humpbacked, and the cervix was lower in VAChT-Cre;NSE-DTA mice than in the control mice during locomotion.

Discussion: These characteristic differences in the gait kinematics might be attributed to a malfunctioning of the motor units with slow-twitch fatigue-resistant and fast-twitch fatigue-resistant types in VAChT-Cre;NSE-DTA mice. The basic description of the locomotor characteristics of this transgenic mouse line may serve as a basis for future comparative analyses.