11th Annual Conference of the International FES Society September 2006 – Zao, Japan
Hindlimb Neuromuscular Stimulation Therapy after Thoracic Contusion Injury Promotes Locomotor Recovery Jung, R 1, Belanger, A 1,2, Kanchiku, T 1, Lynskey, J 1, Mukherjee, M 1,2, Hagner, D 1, Abbas, JJ1,2 1
Center for Adaptive Neural Systems, The Biodesign Institute and 2The Harrington Department of Bioengineering, Arizona State University, PO Box 85287-9709, Tempe, AZ, USA.
[email protected]
Abstract Recovery from incomplete spinal cord injury depends on the degree of injury, intrinsic plasticity of the nervous system and protective and therapeutic interventions. In a novel model of functional neuromuscular stimulation (FNS) based movement therapy in rodents with spinal contusion injuries we assessed the effects of one week of reciprocal hip flexion-extension FNS movement therapy initiated one week post injury. 3D kinematic analysis of treadmill walking with no assistance showed significant recovery of leftright hindlimb coordination with improved symmetry, improved 1:1 hindlimb coordination and reduced variability in quantitative left-right phase relationships of hindlimb touchdown. The recovery was independent of the spinal lesion volume. Immunohistochemical assessment of brainstem-spinal catecholaminergic and serotonergic axon density indicated preservation of select catecholaminergic motor pathways. Thus short-term, early intervention FNS therapy provides improved motor function that is targeted by the therapy and appears to promote plasticity in select populations of descending brainstem spinal motor pathways.
1. INTRODUCTION In the first year after incomplete spinal cord injury (iSCI), substantial improvements in sensorimotor function can occur in part because of inherent plasticity within the central nervous system(5). The pattern and extent of recovery, however, are highly variable and depend upon the nature of injury, the intrinsic adaptive capabilities of the injured central nervous system, and the interventions applied (6). Strategies that tap into or augment the intrinsic plasticity of the nervous system may accelerate and enhance the recovery following iSCI. A promising paradigm for therapeutic intervention
is to provide repeated movement of the limbs using techniques such as robotic assist, treadmill training and/or functional electrical stimulation (1, 2, 7). To assess the mechanism that may underlie functional neuromuscular stimulation (FNS) based movement therapy, we had previously developed a rodent model (4). The therapy is expected to improve motor function and a key component is likely to be the reorganization of the dynamic interaction between the supraspinal and spinal segmental circuitry for motor control of the musculoskeletal system(3). In the current study, we ported this model to a thoracic contusion injury rodent model and investigated the ability of short-term functional neuromuscular stimulation to improve recovery of locomotion and promote plasticity of catecholaminergic supraspinal-spinal pathways believed to contribute to the control of locomotion after iSCI.
2. METHODS 2.1. Overview Long Evans adult female rats were divided into Intact (n=6), iSCI with no therapy (iSCINT, n=4), and iSCI with neuromuscular stimulation therapy groups (iSCIFNS, n=6). The iSCINT and iSCIFNS rats received an incomplete thoracic spinal cord contusion injury (T9, 150kD Infinite Horizon impactor). The hip flexors (iliacus) and extensors (biceps femoralis) of both hindlimbs (HL) of iSCIFNS rats were implanted with custom intramuscular electrodes that were used to administer periodic movement therapy of 15 min/day for 5 days starting 1 week post injury at 2 Hz using a biphasic (40Psec/phase) current pulse train at 75Hz and pulse amplitude of 1.5 times the twitch threshold current. During the therapy, awake animals were supported by a raised platform under the torso and their unloaded HLs were allowed to move freely. The sequence of stimulation was right flex, left extend, left flex, right extend; i.e
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11th Annual Conference of the International FES Society September 2006 – Zao, Japan
displayed 1:1 left-right hindlimb coordination and 56%±22.4% showed 1:1 ipsilateral forelimb-hindlimb coordination. In contrast, in injured rats not receiving therapy, 88%±17.5% of gait cycles displayed 1:1 left-right hindlimb coordination and 62%±22.4% showed 1:1 forelimb-hindlimb coordination. Intact rats displayed 100% 1:1 interlimb coordination. While injury resulted in a decrease in the percent of gait cycles showing 1:1 coordination, there was a significantly lower variability in achieving left-right 1:1 coordination in animals receiving the FNS therapy (p=0.002).
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As seen in the left-right angle-angle plots (5-6
gait cycle average -thick lines, 1 SEM- dashed line) in Figure 1, for intact animals the contours are symmetric about the diagonal reflecting the 180q out of phase left-right coordination. The shapes and symmetry of these contours are considerably altered after injury in the absence of FNS therapy. With therapy, even though impairments remain, the contours are more symmetric and closer in form to those of the intact animals. Quantitative assessment of the symmetry error indicated that the hip joint symmetry error was significantly lower in iSCIFNS rats than in iSCINT rats (8.0°±1.8° vs. 16.7°±2.5°; p=0.03). A similar trend of lower symmetry error was present for the knee (10.8°±1.2° vs. 15.8°±2.7°) and ankle (18.3°±3.3° vs. 21.5°±2.8°). In contrast, intralimb coordination did not improve with therapy (not shown). In intact rats a 1:1 left-right and forelimb-hindlimb coordination is maintained. After iSCI, this 1:1 coordination gets disrupted and multiple touchdown events can occur during one gait cycle. In a time period of 30 seconds in injured rats receiving FNS therapy 97%±3.4% of gait cycles
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reciprocal right-left HL alteration. Introduction of therapy one week after injury allowed early intervention. At the end of the study period (2 weeks post injury; one week of therapy) 3D kinematic analysis of treadmill walking was performed. Joint angle-angle plots were made and a quantitative measure of the symmetry of these plots was obtained to indicate left-right joint angle coordination. The proportion of 1:1 coordinated left and right HL footfalls and ipsilateral forelimb (FL) and HL footfalls was determined and the variability in the phase delays calculated. To assess the neuroanatomical effects of therapy, each animal’s spinal cord was dissected and cryosectioned (20Pm). Immunohistochemical analysis for eriochrome cyanine (lesion reconstruction), tyrosine hydroxlase (catecholaminergic axons), and serotonin transporter (serotonergic axons) was performed on serial sections. Lesion volume and axon density calculations caudal to injury were performed for both catecholaminergic and serotonergic projections to the ventral horn and intermediate gray using Neurolucida, Scion Image and StereoInvestigator, respectively.
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Figure 1. Angle-angle plots illustrate the coordination between the joints of contralateral limbs during treadmill walking in intact, iSCI (14 days post injury) no therapy or iSCI FNS therapy rats. FNS therapy initiated 1 week post injury. The trajectories (average; solid line) +1 SEM (dashed line) show the maximum, minimum, and range of excursion of each joint angle.
Calculation of the phase delay between leftright hindlimb touch downs and ipsilateral forelimb-hindlimb touchdown in those gait cycles in which a single phase event occurred indicated that after injury the left-right phase delay was 0.49±0.020 and forelimb-hindlimb phase delay was 0.28±0.027 for iSCIFNS rats and 0.42±0.068 and 0.29±0.021 respectively for iSCINT rats. Intact rats displayed left-right phase delays of 0.51±0.01 and ipsilateral forelimbhindlimb phase delays of 0.50±0.009. Thus, while there were no significant differences in the phase delays between the injured rats receiving or not receiving therapy, the forelimbhindlimb phase delays for both groups were different from those of the intact animals (p
