Quantitative Evaluation of 3D Mouse Behaviors and Motor Function in the Open-Field after Spinal Cord Injury Using Markerless Motion Tracking

Abstract

Thousands of scientists strive to identify cellular mechanisms that could lead to breakthroughs in developing ameliorative treatments for debilitating neural and muscular conditions such as spinal cord injury (SCI). Most studies use rodent models to test hypotheses, and these are all limited by the methods available to evaluate animal motor function. This study’s goal was to develop a behavioral and locomotor assessment system in a murine model of SCI that enables quantitative kinematic measurements to be made automatically in the open-field by applying markerless motion tracking approaches. Three-dimensional movements of eight naïve, five mild, five moderate, and four severe SCI mice were recorded using 10 cameras (100 Hz). Background subtraction was used in each video frame to identify the animal’s silhouette, and the 3D shape at each time was reconstructed using shape-from-silhouette. The reconstructed volume was divided into front and back halves using k-means clustering. The animal’s front Center of Volume (CoV) height and whole-body CoV speed were calculated and used to automatically classify animal behaviors including directed locomotion, exploratory locomotion, meandering, standing, and rearing. More detailed analyses of CoV height, speed, and lateral deviation during directed locomotion revealed behavioral differences and functional impairments in animals with mild, moderate, and severe SCI when compared with naïve animals. Naïve animals displayed the widest variety of behaviors including rearing and crossing the center of the open-field, the fastest speeds, and tallest rear CoV heights. SCI reduced the range of behaviors, and decreased speed (r = .70 p<.005) and rear CoV height (r = .65 p<.01) were significantly correlated with greater lesion size. This markerless tracking approach is a first step toward fundamentally changing how rodent movement studies are conducted. By providing scientists with sensitive, quantitative measurement methods, subjectivity and human error is reduced, potentially providing insights leading to breakthroughs in treating human disease.

Therapeutic potential of Pak1 inhibition for pain associated with cutaneous burn injury

“…Rearing behavior is associated with general activity level and has been used as a measure of higher order, cognitive-affective/exploratory function in animal models (i.e., more rearing events indicates higher levels of general activity and exploration). 40 – 42 To test rearing, animals were placed into an enclosed box and allowed to freely explore the chamber for a 3-min observation period (see “Methods” section) ( Figure 3(c) ). In all comparisons, animals exhibited a similar number of rearing events at baseline, before or after burn injury, and with romidepsin or DMSO treatment at any testing day (p > 0.05: range across all groups and testing days: 2.8–6.8).…”

A quantitative framework for whole-body coordination reveals specific deficits in freely walking ataxic mice

“…Because of the significant challenges associated with quantifying whole-body coordination in freely walking animals, assessments of mouse motor coordination phenotypes often rely on indirect measures ( Mullen et al, 1976 ; Herbin et al, 2007 ; Lalonde and Strazielle, 2007 ; Guillot et al, 2008 ; Brooks and Dunnett, 2009 ; Cendelin et al, 2010 ; Stroobants et al, 2012 ; Sheets et al, 2013 ; Suidan et al, 2013 ; Camera et al, 2014 ), such as time to fall from a rotarod ( Walter et al, 2006 ; Lalonde and Strazielle, 2007 ) or a fixed bar ( Kim et al, 2009 ; Cendelin, 2014 ), or mis-steps on a ladder ( Vinueza Veloz et al, 2014 ). While these can be sensitive markers for global motor dysfunction, they lack specificity.…”

“…Moreover, several spontaneous mutants have been identified based on visible gait ataxia ( Mullen et al, 1976 ; Walter et al, 2006 ; Lalonde and Strazielle, 2007 ; Cendelin, 2014 ). These mutants exhibit abnormal cell patterning within the cerebellum ( Lalonde and Strazielle, 2007 ; Brooks and Dunnett, 2009 ; Kim et al, 2009 ; Sheets et al, 2013 ; Cendelin, 2014 ). While traditional gait analyses in ataxic mutants have reported a variety of impairments in individual limb movements and interlimb coordination ( Fortier et al, 1987 ; Wang et al, 2006 ; Vinueza Veloz et al, 2014 ), many of these findings are not specific to ataxia and could represent secondary consequences of changes in walking speed ( Batka et al, 2014 ).…”

Gait recovery following spinal cord injury in mice: Limited effect of treadmill training

“…43 More recently, a valid and sensitive automatic 3D kinematic measurement also using markerless motion tracking was developed specifically for mice with SCI. 44…”