D. Michele Basso

Graded histological and locomotor outcomes after spinal cord contusion using the NYU Weight-Drop device versus transection

Injury reproducibility is an important characteristic of experimental models of spinal cord injuries (SCI) because it limits the variability in locomotor and anatomical outcome measures. Recently, a more sensitive locomotor rating scale, the Basso, Beattie, and Bresnahan scale (BBB), was developed but had not been tested on rats with severe SCI complete transection. Rats had a 10-g rod dropped from heights of 6.25, 12.5, 25, and 50 mm onto the exposed cord at Tl 0 using the NYU device. A subset of rats with 25 and 50 mm SCI had subsequent spinal cord transection (SCI + TX) and were compared to rats with transection only (TX) in order to ascertain the dependence of recovery on descending systems. After 7-9 weeks of locomotor testing, the percentage of white matter measured from myelin-stained cross sections through the lesion center was significantly different between all the groups with the exception of 12.5 vs 25 mm and 25 vs 50 mm groups. Locomotor recovery was greatest for the 6.25-mm group and least for the 50-mm group and was correlated positively to the amount of tissue sparing at the lesion center (p < 0.0001). BBB scale sensitivity was sufficient to discriminate significant locomotor differences between the most severe SCI (50 mm) and complete TX (p < 0.01). Transection following SCI resulted in a drop in locomotor scores and rats were unable to step or support weight with their hindlimbs (p < 0.01), suggesting that locomotor recovery depends on spared descending systems. The SCI + TX group had a significantly greater frequency of HL movements during open field testing than the TX group (p < 0.005). There was also a trend for the SCI + TX group to have higher locomotor scores than the TX group (p > 0.05). Thus, spared descending systems appear to modify segmental systems which produce greater behavioral improvements than isolated cord systems.

Behavioral and Histological Outcomes Following Graded Spinal Cord Contusion Injury in the C57Bl/6 Mouse

A computer-controlled electromagnetic spinal cord injury device (ESCID) has been adapted to develop a mouse model of spinal cord contusion injury. In the present study, we have extended this model in C57Bl/6 mice with behavioral and histopathological outcome assessment. Three groups of mice received a laminectomy at the T(9) vertebral level followed by a contusion injury from a predetermined starting load of 1500 dynes. Contusion was produced by rapid displacement of the spinal cord to a peak distance of 0.3, 0.5, or 0.8 mm, with the entire injury and retraction procedure completed over a 23-ms epoch. Control groups received laminectomy alone or complete transection. Functional recovery was examined for 9 weeks after injury using the BBB locomotor rating scale, grid walking, and footprint analysis. Distinct patterns of locomotor recovery were evident across the five groups. Measurements of spared white matter at the epicenter, lesion length, and cross-sectional area of fibronectin-immunopositive scar tissue were also significantly different between injury groups. The severity of injury corresponded with the biomechanical measures recorded at the time of impact as well as with behavioral and histological parameters. The results demonstrate that graded contusion injuries can be produced reliably in mice using the ESCID. The data provide a thorough and quantitative analysis of the effects of contusion injury on long-term behavioral and histological outcome measures in this strain and species.

Remote activation of microglia and pro-inflammatory cytokines predict the onset and severity of below-level neuropathic pain after spinal cord injury in rats

Spinal cord injury (SCI) impairs sensory systems causing chronic allodynia. Mechanisms underlying neuropathic pain have been more extensively studied following peripheral nerve injury (PNI) than after central trauma. Microglial activation, pro-inflammatory cytokine production and activation of p38 MAP kinase pathways may induce at-level allodynia following PNI. We investigated whether midthoracic SCI elicits similar behavioral and cellular responses below the level of injury (lumbar spinal cord; L5). Importantly, we show that anatomical connections between L5 and supraspinal centers remain intact after moderate SCI allowing direct comparison to a well-established model of peripheral nerve injury. We found that SCI elicits below-level allodynia of similar magnitude to at-level pain caused by a peripheral nerve injury. Moreover, the presence of robust microglial activation in L5 cord predicted allodynia in 86% of rats. Also increased phosphorylation of p38 MAP kinase occurred in the L5 dorsal horn of allodynic rats. For below-level allodynia after SCI, TNF-alpha and IL-1beta increased in the L5 dorsal horn by 7 dpo and returned to baseline by 35 dpo. Interestingly, IL-6 remains at normal levels early after SCI and increases at chronic time points. Increased levels of pro-inflammatory cytokines also occurred in the thalamus after SCI-induced allodynia. These data suggest that remote microglial activation is pivotal in the development and maintenance of below-level allodynia after SCI. Fractalkine, a known activator of microglia, and astrocytes were not primary modulators of below-level pain. Although the mechanisms of remote microglial activation are unknown, this response may be a viable target for limiting or preventing neuropathic pain after SCI in humans.

Passive or Active Immunization with Myelin Basic Protein Impairs Neurological Function and Exacerbates Neuropathology after Spinal Cord Injury in Rats

Myelin-reactive T-cells are activated by traumatic spinal cord injury (SCI) in rodents and humans. Despite the historical association of these cells with experimental and clinical neuropathology, recent data suggest a neuroprotective role for myelin-reactive T-cells. Because of the biological and therapeutic implications of these findings, we attempted to reproduce the original neuroprotective vaccine protocols in a model of rat SCI. Specifically, MBP-reactive T-cell function was enhanced in SCI rats via passive or active immunization. Locomotor function was assessed using a standardized locomotor rating scale (Basso–Beattie–Bresnahan scale) and was correlated with myelin and axon sparing. The functional and anatomical integrity of the rubrospinal pathway also was analyzed using the inclined plane test and anatomical tract tracing. MBP-immunized rats exhibited varying degrees of functional impairment, exacerbated lesion pathology, greater rubrospinal neuron loss, increased intraspinal T-cell accumulation, and enhanced macrophage activation relative to SCI control groups. These data are consistent with the conventional view of myelin-reactive T-cells as pathological effector cells.

Behavioral testing after spinal cord injury: congruities, complexities, and controversies.

Selection and implementation of behavioral tests in spinal cord injury research is an important process, and yet few papers have focused on these issues. The critical component of any behavioral experiment is the ability to produce reliable, reproducible, and worthwhile data. Unfortunately, the difference between worthwhile and worthless data is often subtle. This paper describes factors that must be considered in order to select the most sensitive behavioral tests to match the hypothesis of the experiment and apply any test in a standardized, consistent manner. Classifications of behavioral tests, their strengths and limitations, as well as methods to overcome these limitations are discussed. Recent work in translating behavioral tests from rats to mice is also provided. The purpose of this article is to provide a framework by which behavioral testing can be standardized within and across spinal cord injury labs.

Stepwise motor and all-or-none sensory recovery is associated with nonlinear sparing after incremental spinal cord injury in rats.

Spinal cord injury (SCI) causes motor and sensory deficits that impair functional performance. While more functional recovery occurs with greater white matter sparing (WMS), it is unclear which locomotor features are more vulnerable to SCI than others, if recovery of certain features depends on specific amounts of WMS, and whether motor recovery patterns differ from sensory recovery. Locomotor and sensory recovery after graded contusive SCI with cord displacements of 0.3, 0.5, 0.7, 0.9, 1.1, 1.25, and 1.3 mm was examined for 6 weeks in 80 female Sprague-Dawley rats. Seven SCI gradations resulted in three locomotor performance levels measured with BBB (P < 0.01): High: laminectomy (LAM) controls and 0.3 (19.87 +/- 0.35 SEM); Intermediate: 0.5-0.9 (13.71 +/- 0.32); and Low: 1.1-1.3 (9.23 +/- 0.36). Normal paw position was most susceptible to SCI requiring 90% WMS, while consistent plantar stepping was least susceptible depending on 10% WMS. A threshold at the 0.9 severity for coordination, toe clearance, and nearly normal trunk stability and tail usage required 25% WMS. Analysis of interlimb coordination using new phase dispersion (PD) techniques delineated three recovery patterns: synchronous (0.3), modified concordance (0.5, 0.7), and disengaged (0.9, 1.1). Lesion severity correlated to WMS (r(2) = 0.96) and to BBB (r(2) = 0.87) by nonlinear polynomial regressions. Mechanical allodynia developed only after injuries resulting in < or =10% WMS. Nonlinear motor and sensory recovery patterns suggest that small reparative changes may substantially improve function in individuals with SCI. A hierarchical locomotor recovery based on simple segmental versus complex supraspinal motor control is proposed.

Validity of the Walking Scale for Spinal Cord Injury and Other Domains of Function in a Multicenter Clinical Trial

Objective. To demonstrate criterion (concurrent and predictive) and construct validity of the Walking Index for Spinal Cord Injury (WISCI) scale and other walking measures in the Spinal Cord Injury Locomotor Trial (SCILT). Design. Prospective multicenter clinical trial of a walking intervention for patients with acute traumatic spinal cord injury (SCI). Participants/Methods. Body weight−supported treadmill training was compared to overground mobility training in 146 patients with incomplete SCI (C4 to L3) enrolled within 8 weeks of onset and treated for 12 weeks. Primary outcome measures were the Functional Independence Measure (FIM), 50-foot walking speed (50FW-S), and 6-minute walking distance (6MW-D), tested 3, 6, and 12 months after entry. Secondary measures were the Lower Extremity Motor Score (LEMS), Berg Balance Scale (BBS), WISCI, and FIM locomotor score (LFIM), assessed at 6 centers by blinded observers. Data for the 2 arms were combined since no significant differences in outcomes had been found. Results. Correlations with WISCI at 6 months were significant with BBS (r = .90), LEMS (r = .85), LFIM (r = .89), FIM (r = .77), 50FW-S (r = .85), and 6MW-D ( r = .79); similar correlations occurred at 3 and 12 months. Correlations of change scores from baseline WISCI were significant for change scores from baseline of LEMS/BBS/LFIM. Correlation of baseline LEMS and WISCI at 12 months were most significant (r = .73). The R 2 of baseline LEMS explained 57% of variability of WISCI levels at 3 months. Conclusion. Concurrent validity of the WISCI scale was supported by significant correlations with all measures at 3, 6, and 12 months. Correlation of change scores supports predictive validity. The LEMS at baseline was the best predictor of the WISCI score at 12 months and explained most of the variance, which supported both predictive and construct validity. The combination of the LEMS, BBS, WISCI, 50FW-S, and LFIM appears to encompass adequate descriptors for outcomes of walking trials for incomplete SCI.

Role of Matrix Metalloproteinases and Therapeutic Benefits of Their Inhibition in Spinal Cord Injury

SummaryThis review will focus on matrix metalloproteinases (MMPs) and their inhibitors in the context of spinal cord injury (SCI). MMPs have a specific cellular and temporal pattern of expression in the injured spinal cord. Here we consider their diverse functions in the acutely injured cord and during wound healing. Excessive activity of MMPs, and in particular gelatinase B (MMP-9), in the acutely injured cord contributes to disruption of the blood-spinal cord barrier, and the influx of leukocytes into the injured cord, as well as apoptosis. MMP-9 and MMP-2 regulate inflammation and neuropathic pain after peripheral nerve injury and may contribute to SCI-induced pain. Early pharmacologic inhibition of MMPs or the gelatinases (MMP-2 and MMP-9) results in an improvement in long-term neurological recovery and is associated with reduced glial scarring and neuropathic pain. During wound healing, gelatinase A (MMP-2) plays a critical role in limiting the formation of an inhibitory glial scar, and mice that are genetically deficient in this protease showed impaired recovery. Together, these findings illustrate complex, temporally distinct roles of MMPs in SCIs. As early gelatinase activity is detrimental, there is an emerging interest in developing gelatinase-targeted therapeutics that would be specifically tailored to the acute injured spinal cord. Thus, we focus this review on the development of selective gelatinase inhibitors.

Skeletal Muscle Adaptations Following Spinal Cord Contusion Injury in Rat and the Relationship to Locomotor Function: A Time Course Study

Experimental spinal cord injury (SCI) via contusion of moderate severity results in residual locomotor deficits, including a lack of coordination and trunk stability. Given that muscle contractile properties and fiber composition adapt to reduced neural input and/or weight bearing, contusion-induced locomotor deficits may reflect changes in hindlimb skeletal muscle. Therefore, we examined muscle adaptations during early (1 week), intermediate (3 week), and late (10 week) stages of motor recovery after moderate SCI. Forty-two Sprague Dawley rats underwent SCI via 1.1mm cord displacement with the OSU impact device or served as age and weight-matched or laminectomy controls. Subsets of rats had soleus (SOL) in vitro physiological testing or SOL and extensor digitorum longus (EDL) myosin heavy chain (MHC) fiber type analysis. At 1 week post-SCI during paralysis/paresis, a significant decrease in wet weight occurred in the plantaris, medial/lateral gastrocnemius (MG/LG), tibialis anterior, and SOL. Changes in contractile properties of the SOL did not accompany muscle wet weight changes. By 3 weeks, the loss of weight-bearing activity early after SCI induced significant decreases in SOL peak twitch and peak tetanic tension as well as significantly greater IIx MHC expression in the EDL. By 10 weeks post-SCI, after several weeks of weight supported stepping, muscle wet weight, contractile properties and MHC composition returned to baseline levels except for MG/LG atrophy. Thus, muscle plasticity appears to be extremely sensitive to locomotor deficits and their resolution after moderate spinal cord contusion.

Relationship Between ASIA Examination and Functional Outcomes in the NeuroRecovery Network Locomotor Training Program

OBJECTIVE To determine the effects of locomotor training on: (1) the International Standards for Neurological Classification of Spinal Cord Injury examination; (2) locomotion (gait speed, distance); (3) balance; and (4) functional gait speed stratifications after chronic incomplete spinal cord injury (SCI). DESIGN Prospective observational cohort. SETTING Outpatient rehabilitation centers in the NeuroRecovery Network (NRN). PARTICIPANTS Individuals (n=225) with American Spinal Injury Association Impairment Scale (AIS) grade C or D chronic motor incomplete SCI having completed locomotor training in the NRN. INTERVENTION The NRN Locomotor Training Program consists of manual-facilitated body weight-supported standing and stepping on a treadmill and overground. MAIN OUTCOME MEASURES AIS classification, lower extremity pin prick, light touch and motor scores, ten-meter walk and six-minute walk tests, and the Berg Balance Scale. RESULTS Significant gains occurred in lower extremity motor scores but not in sensory scores, and these were only weakly related to gait speed and distance. Final Berg Balance Scale scores and initial lower extremity motor scores were positively related. Although 70% of subjects showed significantly improved gait speed after locomotor training, only 8% showed AIS category conversion. CONCLUSIONS Locomotor training improves gait speed to levels sufficient for independent in-home or community ambulation after chronic motor incomplete SCI. Changes in lower extremity motor and sensory scores do not capture the full extent of functional recovery, nor predict responsiveness to locomotor training. Functional classification based on gait speed may provide an effective measure of treatment efficacy or functional improvement after incomplete SCI.