6. Neuromusculoskeletal modelling and the gain transition of a quadruped according to its speed in rats
This poster details a neuromusculoskeletal model of rat hind limbs during walking and trotting. Toeda and colleagues from Tokyo developed a musculoskeletal model of the fore- and hind limbs of the rat based on empirical anatomical data. To model the muscles, they focused on six prime muscle for the forelimbs, and seven muscles for hind limbs. respectively.
They present a neural system model invoking limb movement control, according to muscle synergy to account for coordinated structure in muscle activities, and postural feedback control, based on shoulder height, hip height and horizontal center of mass velocity. They present simulations of walking and trotting gait, and impose defects of the postural feedback system (by lesions to the cerebellum) to induce unstable gaits and tripping.
Future studies we will explore changes to locomotion speed by shortening the duration of stance phase and investigate dynamic properties of these gaits. We are very excited to meet the authors and learn more about their computational models and robotics platform [Aoi et al. 2013]to emulate the dynamic locomotion of a quadruped. As our DigiGait Imaging System is able to provide numerous metrics of posture and kinematics, such as stride length and rate of limb unloading, over a wide range of gait speeds [0 to 100 cm/s], it is a great instrument to complement the authors’ elegant integrated model of the musculoskeletal and nervous system components.
DigiGait analyzes the gait of laboratory animals over a wide range of walking and running conditions. Numerous metrics of neuromuscular function for each of the four limbs are reported. Limb movement and posture are characterized and quantified, to describe changes coming from defects to the cerebellum, basal ganglia, mucles, nerves, etc. in animals walking voluntary or on a treadmill, up an incline or down a decline.
Video 1: Fine Motor Skills in Fast Running Mice
Mouse executing coordinated stepping at a comfortable walking speed [30 cms/] and very fast running speed [90 cm/s]. Stride length and stride frequency both increase >100% to accommodate the faster speed. The stance phase shortens a greater amount than the swing phase.
5.How ECG Measurements Apply to The Study of Rheumatoid Arthritis and Pain
Dr. Mark Pitcher and colleagues from the NIH tested the hypothesis that exercise and weight control would help reduce pain in rats with rheumatoid arthritis (RA). RA is characterized by pain, reduced mobility, increased weight, and heart problems. Few studies have addressed the benefits of execrice for reducing RA-induced pain and disability.
The researchers studied 4 groups of rats following inection of CFA into the left ankle joint: untreated, weight control, exercise, and weight control+exercise. Outcome measures included nociceptive hypersenstivity, body mass, ankle swelling, and range of motion. The ECGenie was used to measure heart rate (HR) and HR variability, an index of cardiac health.
Their findings suggest that exercise and weight control provided health benefits. The rats with lower body mass exhibited a ~25% increase in HRV. The weight-bearing capacity of the untreated group remained low. Exercise, however, accelerated the return to baseline weight-bearing capacity, an effect that was enhanced by weight control. Though ankle swelling may not have been reduced, exercise improved the range of motion of the joint.
We are quite proud to have provided the ECGenie to aid these researchers in characterizing their novel clinically relevant rat model of RA. Benefits of the ECGenie include speed, ease of use, and simplicity – neither anesthetic nor surgery are required to obtain the electrocardiogram, including all of the PQRST interval durations. HRV measure include time domain, and frequency domain metrics. HRV is reduced in humans and in animals in pain; heart rate and heart rate variability may be useful in assessing pain in animal models of RA.
4. Walk this way: fine motor skills and kinematic gait analysis in ALS mice
This poster presents data that extend previous publications (1-4) of gait disturbances in the SOD1 G93A (G93A) mouse model of amyotrophic lateral sclerosis (ALS), which remains one of the mainstays of in vivo research into the mechanism and treatment of ALS in humans. The G93A mice predictably and reliably demonstrate apparently normal health and motor function through ~6-8 weeks of age, a variety of motor changes at ~ 11-14 weeks, paresis at ~14-16 weeks, paralysis at ~17 weeks, and all die at ~18-20 weeks of age. The DigiGait ventral plane treadmill videography technology has been widely applied (1-4) to study gait in this mouse model, demonstrating a surpanormal gait pre-symptomatically in mice walking horizontally at a comfortable speed (1), and gait disturbances as early as ~5 weeks of age in mice walking up an incline at fast walking speeds (4).
At the upcoming SFN congress, Oksman et al. present their study of gait in freely moving G93A transgenic mice and their wild-type littermates beginning at 8 weeks of age. They report that the coordination of the G93A mice changes beginning at ~11 weeks of age. They show that gait disturbances likely begin in the hind limbs.
The DigiGait Imaging System has shown that one of the earliest evidence of gait disturbances in G93A mice is a narrowing of the hind limb paw placement (4); this poster also describes the hind limb position changing towards the medial axis, ascribing such to increased rigidity. DigiGait, however, illustrates flaccidity in the ankle joint of the mice as they treadmill walk [see Video 1]. Oksman et al. indicate that the swing time increases from 14 weeks of age. The swing time increase may reflect the voluntary slower walking speed of the sick animals. One benefit of the DigiGait imaging system is that the walking speed for all of the animals can be controlled by the researcher throughout the course of the study, ruling out walking speed as the most important confounder in the interpretation of gait disturbances, in people, and in laboratory animals.
- Amende I, Kale A, McCue S, Glazier S, Morgan JP, Hampton TG. Gait dynamics in mouse models of Parkinson’s disease and Huntington’s disease. J Neuroeng Rehabil. 2005 Jul 25;2:20.
- Hampton TG, Amende I. Treadmill gait analysis characterizes gait alterations in Parkinson’s disease and amyotrophic lateral sclerosis mouse models. J Mot Behav. 2010 Jan-Feb;42(1):1-4.
- Mancuso R, Oliván S, Osta R, Navarro X. Evolution of gait abnormalities in SOD1(G93A) transgenic mice. Brain Res. 2011 Aug 11;1406:65-73.
- Vinsant S, Mansfield C, Jimenez-Moreno R, Del Gaizo Moore V, Yoshikawa M, Hampton TG, Prevette D, Caress J, Oppenheim RW, Milligan C. Characterization of early pathogenesis in the SOD1(G93A) mouse model of ALS: part II, results and discussion. Brain Behav. 2013 Jul;3(4):431-57.