Gait is a series of repetitive movements of the limbs used to achieve locomotion. Gait is comprised of step cycles, which are divided into two phases: the stance phase, which is when the foot is moving backwards on the ground to propel the body forwards; and the swing phase, where the foot is off the ground and moving forwards. Disturbances of gait are hallmark features of many neurodegenerative disorders, such as spinal cord injury (SCI), multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS), Parkinson's disease (PD), and stroke; preclinical rodent models of these disorders often recapitulate their respective gait impairments1. The basic control mechanisms of locomotion in mice have been intensively studied2,3. Additionally, there are mouse models of many human neurological disorders4. Gait analysis in mice is therefore an attractive approach to measure multiple aspects of motor deficits that have known anatomical correlates. The study of gait in mouse models may provide insights into the neuropathological bases of locomotor deficits in neurodegenerative disorders, and enable the identification of potential treatments.
Some techniques that have been used to measure gait in rodents include visual inspection (e.g., the Basso mouse scale5 and open field test6) and analysis of gait from the ventral plane7. More recently, methods to measure sagittal plane kinematics of hindlimb movements have gained popularity because they provide more information about the execution of movement and consequently are more sensitive to subtle changes in gait8,9,10,11. Kinematic techniques developed to study hindlimb movement in sagittal plane while walking on a treadmill9,12 have been extensively studied in the context of SCI, ALS, traumatic cortical injuries, stroke, and Huntington's disease8,9,10,11,13,14,15,16. In contrast, these techniques have seen limited use in the study of locomotor deficits for mouse models of multiple sclerosis17.
Experimental autoimmune encephalomyelitis (EAE) is the most commonly used mouse model of MS18. The two main methods of inducing EAE is via active or passive inoculation. In active EAE, mice are immunized with myelin antigens, causing autoreactive T cell-mediated neuroinflammation and demyelination in the spinal cord and cerebellum. Passive EAE, on the other hand, is induced by transferring autoreactive T cells from a mouse with active EAE to a naïve mouse19. As described elsewhere, the disease course and neuropathology are influenced by the central nervous system (CNS) antigen and mouse strain20,21,22,23,24,25. In EAE experiments, control mice are injected with complete Freund's adjuvant (CFA) without the myelin antigen. EAE is characterized by ascending paralysis that begins with tail weakness and can potentially involve the forelimbs, resulting in ataxia and paralysis20. We have recently characterized gait changes in C57Bl/6 mice subjected to myelin oligodendrocyte glycoprotein 35-55 (MOG35-55)-induced EAE. These studies have shown gait analysis to be superior than classical behavioral analysis because deviations from normal ankle movement are highly correlated with the degree of white matter loss in the lumbar spinal cord of EAE mice26. By contrast, the strength of the correlation between white matter loss and two other traditional behavioral measures (clinical scoring and rotarod) was much weaker26.
We describe here the use of kinematic gait analysis to detect movement deficits in the sagittal plane of EAE mice walking on a treadmill. Five reflective markers were placed on a hindlimb to identify movement of the hip, knee, and ankle joints in high-speed video recordings. Motion analysis software was used to extract kinematic data about joint excursions. The utility of these techniques to quantify movement deficits for the MOG35-55 model of EAE are discussed. These techniques are also applicable to the study of gait deficits in other mouse models of neurodegenerative disorders.