Identifying the neural correlates of anticipatory postural control: A novel fMRI paradigm

Altered postural control in the trunk/hip musculature is a characteristic of multiple neurological and musculoskeletal conditions. Previously it was not possible to determine if altered cortical and subcortical sensorimotor brain activation underlies impairments in postural control. This study used a novel fMRI-compatible paradigm to identify the brain activation associated with postural control in the trunk and hip musculature. BOLD fMRI imaging was conducted as participants performed two versions of a lower limb task involving lifting the left leg to touch the foot to a target. For the supported leg raise (SLR) the leg is raised from the knee while the thigh remains supported. For the unsupported leg raise (ULR) the leg is raised from the hip, requiring postural muscle activation in the abdominal/hip extensor musculature. Significant brain activation during the SLR task occurred predominantly in the right primary and secondary sensorimotor cortical regions. Brain activation during the ULR task occurred bilaterally in the primary and secondary sensorimotor cortical regions, as well as cerebellum and putamen. In comparison with the SLR, the ULR was associated with significantly greater activation in the right premotor/SMA, left primary motor and cingulate cortices, primary somatosensory cortex, supramarginal gyrus/parietal operculum, superior parietal lobule, cerebellar vermis, and cerebellar hemispheres. Cortical and subcortical regions activated during the ULR, but not during the SLR, were consistent with the planning, and execution of a task involving multisegmental, bilateral postural control. Future studies using this paradigm will determine mechanisms underlying impaired postural control in patients with neurological and musculoskeletal dysfunction.

Increased Brain Sensorimotor Network Activation after Incomplete Spinal Cord Injury

After complete spinal cord injury (SCI), activation during attempted movement of paralyzed limbs is sharply reduced, but after incomplete SCI-the more common form of human injury-it is unknown how attempts to move voluntarily are accompanied by activation of brain motor and sensory networks. Here, we assessed brain activation during ankle movement in subjects with incomplete SCI, among whom voluntary motor function is partially preserved. Adults with incomplete SCI (n = 20) and healthy controls (n = 15) underwent functional magnetic resonance imaging that alternated rest with 0.3-Hz right ankle dorsiflexion. In both subject groups, ankle movement was associated with bilateral activation of primary and secondary sensory and motor areas, with significantly (p < 0.001) greater activation in subjects with SCI within right hemisphere areas, including primary sensorimotor cortex and pre-motor cortex. This result was further evaluated using linear regression analysis with respect to core clinical variables. Poorer locomotor function correlated with larger activation within several right hemisphere areas, including pre- and post-central gyri, possibly reflecting increased movement complexity and effort, whereas longer time post-SCI was associated with larger activation in left post-central gyrus and bilateral supplementary motor area, which may reflect behaviorally useful adaptations. The results indicate that brain adaptations after incomplete SCI differ sharply from complete SCI, are related to functional behavioral status, and evolve with increasing time post-SCI. The results suggest measures that might be useful for understanding and treating incomplete SCI in human subjects.

Robotic Rehabilitator of the Rodent Upper Extremity: A System and Method for Assessing and Training Forelimb Force Production after Neurological Injury

Rodent models of spinal cord injury are critical for the development of treatments for upper limb motor impairment in humans, but there are few methods for measuring forelimb strength of rodents, an important outcome measure. We developed a novel robotic device--the Robotic Rehabilitator of the Rodent Upper Extremity (RUE)--that requires rats to voluntarily reach for and pull a bar to retrieve a food reward; the resistance of the bar can be programmed. We used RUE to train forelimb strength of 16 rats three times per week for 23 weeks before and 38 weeks after a mild (100 kdyne) unilateral contusion at the cervical level 5 (C5). We measured maximum force produced when RUE movement was unexpectedly blocked. We compared this blocked pulling force (BPF) to weekly measures of forelimb strength obtained with a previous, well-established method: the grip strength meter (GSM). Before injury, BPF was 2.6 times higher (BPF, 444.6 ± 19.1 g; GSM, 168.4 ± 3.1 g) and 4.9 times more variable (p < 0.001) than pulling force measured with the GSM; the two measurement methods were uncorrelated (R(2) = 0.03; p = 0.84). After injury, there was a significant decrease in BPF of 134.35 g ± 14.71 g (p < 0.001). Together, our findings document BPF as a repeatable measure of forelimb force production, sensitive to a mild spinal cord injury, which comes closer to measuring maximum force than the GSM and thus may provide a useful measure for quantifying the effects of treatment in rodent models of SCI.

Targeted engagement of a dorsal premotor circuit in the treatment of post-stroke paresis

BACKGROUND

Good motor outcome after stroke has been found to correlate with increased activity in a dorsal premotor (PMd) brain circuit, suggesting that therapeutic strategies targeting this circuit might have a favorable, causal influence on motor status.

OBJECTIVE

This study addressed the hypothesis that a Premotor Therapy that exercises normal PMd functions would provide greater behavioral gains than would standard Motor Therapy; and that Premotor Therapy benefits would be greatest in patients with greater preservation of PMd circuit elements.

METHODS

Patients with chronic hemiparetic stroke (n = 15) were randomized to 2-weeks of Premotor Therapy or Motor Therapy, implemented through a robotic device.

RESULTS

Overall, gains were modest but significant (change in FM score, 2.1 ± 2.8 points, p < 0.02) and did not differ by treatment assignment. However, a difference between Therapies was apparent when injury to the PMd circuit was considered, as the interaction between treatment assignment and degree of corticospinal tract injury was significantly related to the change in FM score (p = 0.018): the more the corticospinal tract was spared, the greater the gains provided by Premotor Therapy. Similar results were obtained when looking at the interaction between treatment assignment and PMd function (p = 0.03).

CONCLUSIONS

Targeted engagement of a brain circuit is a feasible strategy for stroke rehabilitation. This approach has maximum impact when there is less stroke injury to key elements of the targeted circuit.

A re-assessment of treatment with a tyrosine kinase inhibitor (imatinib) on tissue sparing and functional recovery after spinal cord injury

This study was undertaken as part of the NIH "Facilities of Research Excellence-Spinal Cord Injury" project to support independent replication of published studies. Here, we repeat key parts of a study reporting that rats treated with imatinib (Gleevec®, Novartis) after spinal cord contusion injury exhibited enhanced bladder function, greater recovery of motor function, and increased tissue sparing. Young adult female SCA Sprague-Dawley rats received moderate contusion injuries at T9-T10 using the MASCIS weight drop device. One group (n=16) received oral doses of imatinib 30min after injury and then daily doses for 5days. A control group (n=18) received vehicle. Motor function was assessed with the BBB locomotor rating scale and a contact plantar placement task. Bladder function was assessed by measuring the amount of urine retained in the bladder. Tissue preservation was assessed by immunostaining and stereological analysis. Rats that received imatinib had lower volumes of retained urine, suggesting improved bladder function, but there were no significant differences in motor function on any of the other tasks. Tissue preservation was assessed by immunostaining and stereological analysis. Quantitative analysis of spared tissue, cyst size, spared white matter, and inflammatory cell invasion revealed no significant differences between imatinib treated and control rats. Taken together our results confirm the findings that treatment with imatinib improves bladder function after SCI but fail to replicate findings of improved motor function, enhanced tissue sparing, and decreased inflammatory cell invasion.

Salmon fibrin treatment of spinal cord injury promotes functional recovery and density of serotonergic innervation

The neural degeneration caused by spinal cord injury leaves a cavity at the injury site that greatly inhibits repair. One approach to promoting repair is to fill the cavity with a scaffold to limit further damage and encourage regrowth. Injectable materials are advantageous scaffolds because they can be placed as a liquid in the lesion site then form a solid in vivo that precisely matches the contours of the lesion. Fibrin is one type of injectable scaffold, but risk of infection from blood borne pathogens has limited its use. We investigated the potential utility of salmon fibrin as an injectable scaffold to treat spinal cord injury since it lacks mammalian infectious agents and encourages greater neuronal extension in vitro than mammalian fibrin or Matrigel®, another injectable material. Female rats received a T9 dorsal hemisection injury and were treated with either salmon or human fibrin at the time of injury while a third group served as untreated controls. Locomotor function was assessed using the BBB scale, bladder function was analyzed by measuring residual urine, and sensory responses were tested by mechanical stimulation (von Frey hairs). Histological analyses quantified the glial scar, lesion volume, and serotonergic fiber density. Rats that received salmon fibrin exhibited significantly improved recovery of both locomotor and bladder function and a greater density of serotonergic innervation caudal to the lesion site without exacerbation of pain. Rats treated with salmon fibrin also exhibited less autophagia than those treated with human fibrin, potentially pointing to amelioration of sensory dysfunction. Glial scar formation and lesion size did not differ significantly among groups. The pattern and timing of salmon fibrin's effects suggest that it acts on neuronal populations but not by stimulating long tract regeneration. Salmon fibrin clearly has properties distinct from those of mammalian fibrin and is a beneficial injectable scaffold for treatment of spinal cord injury.

A re-assessment of a combinatorial treatment involving Schwann cell transplants and elevation of cyclic AMP on recovery of motor function following thoracic spinal cord injury in rats

This study was undertaken as part of the NIH "Facilities of Research-Spinal Cord Injury" project to support independent replication of published studies. Here, we repeated a study reporting that a combinatorial treatment with transplants of Schwann cells, systemic delivery of Rolipram to enhance cyclic AMP levels, and intra-spinal injections of dibutyryl cyclic AMP enhanced locomotor recovery in rats after contusion injuries at the thoracic level. We compared the following experimental groups: 1) rats that received Schwann cell transplants, systemic Rolipram, and injections of db-cyclic AMP (the combined treatment group that showed the greatest improvement in function); 2) rats that received Schwann cell transplants only and implantation of empty pumps as control; 3) rats that received Rolipram only and implantation of empty pumps as control, and 4) control rats that received no treatment other than the injection of DMEM into the spinal cord and implantation of empty pumps. The principal findings reported in Pearse et al. were not replicated in that the combined treatment group did not exhibit greater recovery on any of the measures, although the group that received Schwann cells only did exhibit enhanced recovery on several of the outcome measures. The failure of the combined treatment may be due in part to less successful engraftment of Schwann cells in our study vs. Pearse et al. Issues relating to failures to replicate, especially when effect size is small, are discussed.

Forelimb locomotor assessment scale (FLAS): novel assessment of forelimb dysfunction after cervical spinal cord injury

We describe here a novel forelimb locomotor assessment scale (FLAS) that assesses forelimb use during locomotion in rats injured at the cervical level. A quantitative scale was developed that measures movements of shoulder, elbow, and wrist joints, forepaw position and digit placement, forelimb-hindlimb coordination, compensatory behaviors adopted while walking, and balance. Female Sprague-Dawley rats received graded cervical contusions ranging from 200 to 230 ("mild," n=11) and 250-290 kdyn ("moderate," n=13) between C5 and C8. Rats were videotaped post-injury as they walked along an alley to determine deficits and recovery of forelimb function. Recovery of shoulder and elbow joint movement occurred rapidly (within 1-7 days post-injury), whereas recovery of wrist joint movement was slower and more variable. Most rats in all groups displayed persistent deficits in forepaw and digit movement, but developed compensatory behaviors to allow functional forward locomotion within 1-2 weeks post-injury. Recovery of forelimb function as measured by the FLAS reached a plateau by 3 weeks post-injury in all groups. Rats with mild contusions displayed greater locomotor recovery than rats with moderate contusions, but exhibited persistent deficits compared to sham controls. Reliability was tested by having seven raters (three internal, four external) from different laboratories, independently and blindly score videos of all rats. The multivariate correlation between all raters, all animals, and all time points ranged from r(2)=0.88-0.96 (p<0.0001), indicating a high inter-rater reliability. Thus, the FLAS is a simple, inexpensive, sensitive, and reliable measure of forelimb function during locomotion following cervical SCI.

Bilateral cervical contusion spinal cord injury in rats

There is increasing motivation to develop clinically relevant experimental models for cervical SCI in rodents and techniques to assess deficits in forelimb function. Here we describe a bilateral cervical contusion model in rats. Female Sprague-Dawley rats received mild or moderate cervical contusion injuries (using the Infinite Horizons device) at C5, C6, or C7/8. Forelimb motor function was assessed using a grip strength meter (GSM); sensory function was assessed by the von Frey hair test; the integrity of the corticospinal tract (CST) was assessed by biotinylated dextran amine (BDA) tract tracing. Mild contusions caused primarily dorsal column (DC) and gray matter (GM) damage while moderate contusions produced additional damage to lateral and ventral tissue. Forelimb and hindlimb function was severely impaired immediately post-injury, but all rats regained the ability to use their hindlimbs for locomotion. Gripping ability was abolished immediately after injury but recovered partially, depending upon the spinal level and severity of the injury. Rats exhibited a loss of sensation in both fore- and hindlimbs that partially recovered, and did not exhibit allodynia. Tract tracing revealed that the main contingent of CST axons in the DC was completely interrupted in all but one animal whereas the dorsolateral CST (dlCST) was partially spared, and dlCST axons gave rise to axons that arborized in the GM caudal to the injury. Our data demonstrate that rats can survive significant bilateral cervical contusion injuries at or below C5 and that forepaw gripping function recovers after mild injuries even when the main component of CST axons in the dorsal column is completely interrupted.