Abstract
In rodents, detection and quantification of motor impairments is difficult. The traction test (inverted grid with mice clinging to the underside) currently has no objective rating system. We here developed and validated the semi-automatic MATLAB script TracMouse for unbiased detection of video-recorded movement patterns. High precision videos were analyzed by: (i) principal identification of anatomical paw details frame-by-frame by an experimentally blinded rater; (ii) automatic retrieval of proxies by TracMouse for individual paws. The basic states of Hold and Step were discriminated as duration and frequency, and these principle parameters were converted into static and dynamic endpoints and their discriminating power assessed in a dopaminergic lesion model. Relative to hind paws, forepaws performed ~4 times more steps, they were ~20% longer, and Hold duration was ~5 times shorter in normal C57Bl/6 mice. Thus, forepaw steps were classified as exploratory, hind paw movement as locomotive. Multiple novel features pertaining to paw sequence, step lengths and exploratory touches were accessible through TracMouse and revealed subtle Parkinsonian phenotypes. Novel proxies using TracMouse revealed previously unidentified features of movement and may aid the understanding of (i) brain circuits related to motor planning and execution, and (ii) phenotype detection in experimental models of movement disorders.
Highlights
Of paws across the grid, without real initiation of movement)
According to Tillerson et al.[12] the three measures of inverted grid performance were superior in their sensitivity to reveal the effects of MPTP on forepaw movement in retired breeders of C57BL/6 mice; deficits were more robust and correlational compared to activity monitoring, Rotarod, and forepaw stride length during walking
The somewhat better performance in these treatment groups over MPTP alone significantly correlated with content of striatal dopamine (DA), dopamine transporter (DAT), vesicular monoamine transporter 2 (VMAT2) and tyrosine hydroxylase (TH) suggesting that recovery in these neurochemical markers is sufficient for treatment-related improvement in motor function
Summary
Of paws across the grid, without real initiation of movement). Steps were further denominated as successful or unsuccessful such that movement of a paw to another area and placement with fingers around the grid constituted the former, while slipping or a failure to place the paw at a new grid location constituted the latter. A difficulty inherent to this approach is the subjectivity with which data were categorized They required a “rater experienced in behavioral analysis of rodents”[11], and especially the successful/unsuccessful classification is prone to failure. If this rating becomes ambiguous, does the parameter of Percent Forepaw Faults and Average Forepaw Step Distance collapse and this would render the whole approach questionable. From high resolution video images, an experimenter marked the paw position during ‘Hold’ frame by frame on screen, extracted hold-related parameters and auto-analyzed any movement related shift of the paw using a MATLAB based script This enabled unbiased detection of forepaw/hind paw activity. We included a small cohort treated with MPTP to confirm phenotypes reported in the literature, and to reveal the sensitivity of the new analysis tool TracMouse qualitatively
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