Cellular morphology of chronic spinal cord injury in the cat: analysis of myelinated axons by line-sampling

NG2 cell response in the CNP-EGFP mouse after contusive spinal cord injury

NG2(+) cells in the adult CNS are a heterogeneous population. The extent to which the subpopulation of NG2(+) cells that function as oligodendrocyte progenitor cells (OPCs) respond to spinal cord injury (SCI) and recapitulate their normal developmental progression remains unclear. We used the CNP-EGFP mouse, in which oligodendrocyte lineage cells express EGFP, to study NG2(+) cells in the normal and injured spinal cord. In white matter of uninjured mice, bipolar EGFP(+)NG2(+) cells and multipolar EGFP(neg)NG2(+) cells were identified. After SCI, EGFP(+)NG2(+) cell proliferation in residual white matter peaked at 3 days post injury (DPI) rostral to the epicenter, while EGFP(neg)NG2(+) cell proliferation peaked at 7 DPI at the epicenter. The expression of transcription factors, Olig2, Sox10, and Sox17, and the basic electrophysiological membrane parameters and potassium current phenotype of the EGFP(+)NG2(+) population after injury were consistent with those of proliferative OPCs during development. EGFP(neg)NG2(+) cells did not express transcription factors involved in oligodendrogenesis. EGFP(+)CC1(+) oligodendrocytes at 6 weeks included cells that incorporated BrdU during the peak of EGFP(+)NG2(+) cell proliferation. EGFP(neg)CC1(+) oligodendrocytes were never observed. Treatment with glial growth factor 2 and fibroblast growth factor 2 enhanced oligodendrogenesis and increased the number of EGFP(neg)NG2(+) cells. Therefore, based on EGFP and transcription factor expression, spatiotemporal proliferation patterns, and response to growth factors, two populations of NG2(+) cells can be identified that react to SCI. The EGFP(+)NG2(+) cells undergo cellular and physiological changes in response to SCI that are similar to those that occur in early postnatal NG2(+) cells during developmental oligodendrogenesis.

Acute rolipram/thalidomide treatment improves tissue sparing and locomotion after experimental spinal cord injury

Traumatic spinal cord injury (SCI) causes severe and permanent functional deficits due to the primary mechanical insult followed by secondary tissue degeneration. The cascade of secondary degenerative events constitutes a range of therapeutic targets which, if successfully treated, could significantly ameliorate functional loss after traumatic SCI. During the early hours after injury, potent pro-inflammatory cytokines, including tumor necrosis factor alpha (TNF-alpha) and interleukin-1 beta (IL-1beta) are synthesized and released, playing key roles in secondary tissue degeneration. In the present investigation, the ability of rolipram and thalidomide (FDA approved drugs) to reduce secondary tissue degeneration and improve motor function was assessed in an experimental model of spinal cord contusion injury. The combined acute single intraperitoneal administration of both drugs attenuated TNF-alpha and IL-1beta production and improved white matter sparing at the lesion epicenter. This was accompanied by a significant (2.6 point) improvement in the BBB locomotor score by 6 weeks. There is, at present, no widely accepted intervention strategy that is appropriate for the early treatment of human SCI. The present data suggest that clinical trials for the acute combined application of rolipram and thalidomide may be warranted. The use of such "established drugs" could facilitate the early initiation of trials.

Intraspinal MDL28170 microinjection improves functional and pathological outcome following spinal cord injury

Although calpain (calcium-activated cysteine protease) inhibition represents a rational therapeutic target for spinal cord injury (SCI), few studies have reported improved functional outcomes with post-injury administration of calpain inhibitors. This reflects the weak potency and limited aqueous solubility of current calpain inhibitors. Previously, we demonstrated that intraspinal microinjection of the calpain inhibitor MDL28170 resulted in greater inhibition of calpain activity as compared to systemic administration of the same compound. In the present study, we evaluated the ability of intraspinal MDL28170 microinjection to spare spinal tissue and locomotor dysfunction following SCI. Contusion SCI was produced in female Long-Evans rats using the Infinite Horizon impactor at the 200-kdyn force setting. Open-field locomotion was evaluated until 6 weeks post-injury. Histological assessment of tissue sparing was performed at 6 weeks after SCI. The results demonstrate that MDL28170, administered with a single post-injury intraspinal microinjection (50 nmoles), significantly improves both locomotor function and pathological outcome measures following SCI.

Descending pathways in motor control

Each of the descending pathways involved in motor control has a number of anatomical, molecular, pharmacological, and neuroinformatic characteristics. They are differentially involved in motor control, a process that results from operations involving the entire motor network rather than from the brain commanding the spinal cord. A given pathway can have many functional roles. This review explores to what extent descending pathways are highly conserved across species and concludes that there are actually rather widespread species differences, for example, in the transmission of information from the corticospinal tract to upper limb motoneurons. The significance of direct, cortico-motoneuronal (CM) connections, which were discovered a little more than 50 years ago, is reassessed. I conclude that although these connections operate in parallel with other less direct linkages to motoneurons, CM influence is significant and may subserve some special functions including adaptive motor behaviors involving the distal extremities.

Alarm criteria for motor-evoked potentials: what's wrong with the "presence-or-absence" approach?

STUDY DESIGN

Combined prospective and retrospective.

OBJECTIVE

Evaluate 2 published criteria for interpreting motor-evoked potentials (MEP) in response to repetitive transcranial electrical stimulation (rTES) during surgery.

SUMMARY OF BACKGROUND DATA

There is controversy regarding how to interpret MEPs elicited by rTES. Many centers warn the surgical team only if the MEP is lost entirely ("Presence-or-Absence" method). Alternatively, we monitor the stimulus energy needed to elicit a minimal evoked EMG response; significant increases in this energy reflect impending motor tract injury and serve as the basis for warning the surgical team ("Threshold-Level" method).

METHODS

We documented target muscle thresholds for rTES throughout each subject's surgical procedure. The time (in hours) between intraoperative threshold change and (a) complete loss of response or (b) until the end of the surgical procedure was determined. Short-term postoperative motor status was documented by either direct physical examination or by chart review.

RESULTS

We enrolled 903 subjects, from whom intraoperative rTES-evoked responses could be elicited in 859 subjects. Of these, 93 subjects sustained intraoperative damage to central motor pathways. Significant increases in target muscle thresholds were often noted many minutes, and sometimes hours before complete signal loss. In other cases, thresholds increased significantly without ever losing the muscle response.

CONCLUSION

The Threshold-Level method is highly sensitive and specific to deterioration in central motor function, and provides early warning of such an event. Conversely, in some cases the Presence-or-Absence method may fail to detect episodes of partial loss, and in other cases typically introduces a delay between the times when motor dysfunction begins to occur and when the response is lost (at which time an alarm is triggered). We conclude that use of the Presence-or-Absence alarm criteria for interpreting MEPs during surgery is often incompatible with the requirement for accurate and early warning of impending injury to central motor pathways, and should be avoided.

Reticulospinal pathways in the ventrolateral funiculus with terminations in the cervical and lumbar enlargements of the adult rat spinal cord

In the mammalian spinal cord, the ventrolateral funiculus (VLF) has been identified as critical to postural control and locomotor function, in part due to the reticulospinal pathways it contains. The primary purpose of this descriptive study was to investigate the distribution of neurons in the medulla labeled retrogradely from the VLF and the intermediate gray matter of specific lumbar and cervical spinal cord segments in the adult rat. We made discrete injections of Fluoro-Ruby (FR) into the intermediate gray matter at the cervical (C) 5/6, 7/8 or lumbar (L) 2 segmental levels followed by a single injection of Fluoro-Gold (FG) into the right VLF at T9. Double-labeled medullary neurons were found primarily in the gigantocellular group of nuclei (Gi), distributed both ipsilaterally and contralaterally following cervical or lumbar FR injections. In addition, a substantial population of neurons contained within the vestibular group of nuclei was double labeled both ipsilaterally and contralaterally. We also identified a substantial population of Gi-related neurons located ipsilateral to the VLF injections that were double labeled following left unilateral FR injections at C5/6, C7/8 or L2. These results describe a substantial population of ipsilateral and commissural medullary neurons that project to both cervical and thoracolumbar segments. Two different populations of commissural neurons are described, one with axons that cross the midline rostral to T9, and one with axons that cross the midline caudal to T9. These observations provide strong additional evidence for a pattern of reticulo- and vestibulospinal projections that include substantial numbers of commissural neurons and project to multiple cervical and thoracolumbar levels.

Selenium attenuates ROS-mediated apoptotic cell death of injured spinal cord through prevention of mitochondria dysfunction; in vitro and in vivo study

The primary objective of this study was to determine the possible apoptotic cell death preventive effects of the antioxidant selenium using an experimental rat spinal cord injury (SCI) model and cultured spinal cord-derived neural progenitor cells (NPCs). Sodium selenite treatment exerted a profound preventive effect on apoptotic cell death, including p-P38, p-SAPK/JNK, caspases, and PARP activity, and ameliorated astrogliosis and hypomyelination, which occurs in regions of active cell death in the spinal cords of SCI rats. The foremost protective effect of selenite in SCI would therefore be manifested in the suppression of acute secondary apoptotic cell death. However, selenite does not appear to exert an anti-inflammatory function associated with active microglia and macrophage propagation or infiltration into the lesion site. Selenite-mediated neuroprotection has been linked to selenite's attenuation or inhibition of p38 mitogen-activated protein kinase, pSAPK/JNK, and Bax activation in in vitro and in vivo SCI lesion sites. Selenite also attenuated cell death via the prevention of cytochrome c release, caspase activation, and ROS accumulation in the cytosol. Also, our study showed that selenite administered immediately after SCI significantly diminishes functional deficits. The selenite-treated group recovered hind limb reflexes more rapidly, and a higher percentage of these rats regained responses to a greater degree than was seen in the untreated injured rats. Our data indicate that the therapeutic outcome of selenite is most likely the consequence of its comprehensive apoptotic cell death blocking effects, resulting in the protection of white matter, oligodendrocytes, and neurons, and the inhibition of astrogliosis. The finding that the administration of selenite prevents secondary pathological events in traumatic spinal cord injuries, and promotes the recovery of motor function in an animal model. Its efficacy may facilitate the development of novel drug targets for the treatment of SCI.

The extent of myelin pathology differs following contusion and transection spinal cord injury

Demyelination is a prominent feature of spinal cord injury (SCI) and is followed by incomplete remyelination, which may contribute to physiological impairment. Demyelination has been documented in several species including humans, but the extent of demyelination and its functional consequence remain unknown. In this report, we document and compare the extent of tissue pathology, white matter apoptosis, demyelination, and remyelination 2 months following injury in rat contusion and transection models of SCI. Moreover, we document and compare the macrophage response 3 and 14 days post contusion and transection SCI. Contusion injury resulted in widespread tissue pathology, white matter apoptosis, demyelination, incomplete remyelination, and robust macrophage response extending several millimeters cranial and caudal to the epicenter of injury. In contrast, transection injury resulted in focal tissue pathology with white matter apoptosis, demyelination, incomplete remyelination, and robust macrophage response at the epicenter of injury, and little pathologic features at a distance from the epicenter of injury, as indicated by the lack of apoptosis and demyelination. These data indicate for the first time that myelin pathology differs substantially following contusion and transection SCI.

Functional magnetic resonance imaging within the rat spinal cord following peripheral nerve injury

Functional magnetic resonance imaging (fMRI) was used to detect the effects of graded peripheral nerve injury at the spinal level. Graded peripheral nerve injury in rats was accomplished by transection of nerves entering the spinal cord at the L3 and L4 levels of the spinal cord segments. Electrical stimulation of the hindpaw was used to elicit activity within the spinal cord. The stimulation experimental paradigm consisted of 62 functional images, 5 slices each, with a total of 3 rest and 2 stimulation periods. A 9.4 T MRI system and a quadrature volume rf coil covering the lumbar spinal cord were used for the fMRI study. Sets of fast spin echo images were acquired repeatedly following sham preparatory surgery under control conditions and in rats following sham surgery (pre nerve cut), followed by L3 nerve and then L4 nerve section. In rats with sham surgery, there was a significant activation within the dorsal horn of slices corresponding to L3 and L4 spinal cord segments. Following section of the L3 nerve, there was a reduction in the number of active voxels in the L3 and L4 spinal cord segments. The activation was reduced further by sectioning of the L4 nerve. Thus, following an increasing loss of axonal connections to the spinal cord, there was a decreasing number of active voxels within the spinal cord. The results demonstrate that spinal fMRI in the rat has sufficient sensitivity to detect within the spinal cord the effects of a graded reduction in peripheral connectivity.

4-Aminopyridine derivatives enhance impulse conduction in guinea-pig spinal cord following traumatic injury

4-Aminopyridine (4-AP), a potassium channel blocker, is capable of restoring conduction in the injured spinal cord. However, the maximal tolerated level of 4-AP in humans is 100 times lower than the optimal dose in in vitro animal studies due to its substantially negative side effects. As an initial step toward the goal of identifying alternative potassium channel blockers with a similar ability of enhancing conduction and with fewer side effects, we have synthesized structurally distinct pyridine-based blockers. Using isolated guinea-pig spinal cord white matter and a double sucrose gap recording device, we have found three pyridine derivatives, N-(4-pyridyl)-methyl carbamate (100 microM), N-(4-pyridyl)-ethyl carbamate (100 microM), and N-(4-pyridyl)-tertbutyl (10 microM) can significantly enhance conduction in spinal cord white matter following stretch. Similar to 4-AP, the derivatives did not preferentially enhance conduction based on axonal caliber. Unlike 4-AP, the derivatives did not change the overall electrical responsiveness of axons to multiple stimuli, indicating the axons recruited by the derivatives conducted in a manner similar to healthy axons. These results demonstrate the ability of novel constructs to serve as an alternative to 4-AP for the purpose of reversing conduction deficits.

Mixed primary culture and clonal analysis provide evidence that NG2 proteoglycan-expressing cells after spinal cord injury are glial progenitors

NG2(+) cells in the adult rat spinal cord proliferate after spinal cord injury (SCI) and are postulated to differentiate into mature glia to replace some of those lost to injury. To further study these putative endogenous precursors, tissue at 3 days after SCI or from uninjured adults was dissociated, myelin partially removed and replicate cultures grown in serum-containing or serum-free medium with or without growth factors for up to 7 days in vitro (DIV). Cell yield after SCI was 5-6 times higher than from the normal adult. Most cells were OX42(+) microglia/macrophages but there were also more than twice the normal number of NG2(+) cells. Most of these coexpressed A2B5 or nestin, as would be expected for glial progenitors. Few cells initially expressed mature astrocyte (GFAP) or oligodendrocyte (CC1) markers, but more did at 7 DIV, suggesting differentiation of glial precursors in vitro. To test the hypothesis that NG2(+) cells after SCI express progenitor-like properties, we prepared free-floating sphere and single cell cultures from purified suspension of NG2(+) cells from injured spinal cord. We found that sphere cultures could be passaged in free-floating subcultures, and upon attachment the spheres clonally derived from an acutely purified single cell differentiated into oligodendrocytes and rarely astrocytes. Taken together, these data support the hypothesis that SCI stimulates proliferation of NG2(+) cells that are glial progenitor cells. Better understanding the intrinsic properties of the NG2(+) cells stimulated by SCI may permit future therapeutic manipulations to improve recovery after SCI.

Temporal-spatial dynamics in oligodendrocyte and glial progenitor cell numbers throughout ventrolateral white matter following contusion spinal cord injury

The aim of this study was to systematically determine the spatial distribution of oligodendrocytes (CC1(+)) and glial progenitor cells (NG2(+)) throughout the ventral lateral funiculi (VLF) of adult rat thoracic spinal cord white matter over the course of spontaneous hindlimb locomotor recovery following moderate contusion injury. We used the optical fractionator technique to establish an unbiased estimate of total CC1(+) and NG2(+) cell numbers throughout equivalent segments of VLF from normal and injured spinal cords at designated time points. The results demonstrated a greater than 60% loss of oligodendrocytes and a 50% increase in NG2(+) cells 2 days postinjury. Subsequently, there was a significant increase in oligodendrocytes 7 days postinjury that continued throughout the time course of our experiments (42 days) when the total numbers recovered to 80% of controls. Conversely, NG2(+) cell numbers progressively declined after 2 days postinjury but remained significantly higher than controls throughout the experiments. The pattern of acute loss and repopulation of oligodendrocytes in the VLF paralleled the initial recovery of hindlimb weight-bearing function. Whether such improvement is directly related to NG2(+) cell differentiation into functional oligodendrocytes is uncertain. However, of critical importance is that significant cellular dynamics occurred primarily distal to the injury, and these changes were mirrored by significant alterations in the expression of mature myelin proteins. This infers that site-specific genetic or cellular interventions designed to enhance locomotor recovery by fostering remyelination of spared and/or newly established relay circuits may need to target not only the injury site but also rostrocaudal regions.

Glial cell loss, proliferation and replacement in the contused murine spinal cord

Studies in the rat have shown that contusive spinal cord injury (SCI) results in devastating pathology, including significant loss of mature oligodendrocytes and astrocytes even in spared white matter. Subsequently, there is increased proliferation of endogenous NG2(+) cells, postulated to contribute to replacement of mature glia chronically, which is important for functional recovery. Studies of mechanisms that stimulate endogenous progenitor cells would be facilitated by using mouse models with naturally occurring and genetically engineered mutations. To determine whether the murine response is similar to that in the rat, we performed contusive SCI on adult female C57Bl/6 mice at the T8-9 level. Animals received bromodeoxyuridine injections in the first week following injury and were killed at 1, 3, 4, 7 or 28 days postinjury (DPI). The overall loss of macroglia and the temporal-spatial response of NG2(+) cells after SCI in the (C57Bl/6) mouse was very similar to that in the (Sprague-Dawley) rat. By 24 h after SCI nearly half of the macroglia in spared ventral white matter had been lost. Cell proliferation was increased at 1-7 DPI, peaking at 3-4 DPI. Dividing cells included NG2(+) cells and Cd11b(+) macrophages and microglia. Furthermore, cells dividing in the first week expressed markers of mature glia at 28 DPI. The similarities in endogenous progenitor cell response to SCI in the mouse and rat suggest that this is a fundamental injury response, and that transgenic mouse models may be used to further probe how this cellular response to SCI might be enhanced to improve recovery after SCI.

Sustained calpain inhibition improves locomotor function and tissue sparing following contusive spinal cord injury

Following contusive spinal cord injury (SCI), calpain activity is dramatically increased and remains elevated for days to weeks. Although calpain inhibition has previously been demonstrated to be neuroprotective following spinal cord injury, most studies administered the calpain inhibitor at a single time point. We hypothesized that sustained calpain inhibition would improve functional and pathological outcomes, as compared to the results obtained with a single postinjury administration of the calpain inhibitor. Contusion SCI was produced in female Long-Evans rats using the Infinite Horizon spinal cord injury impactor at the 200 kdyn force setting. Open-field locomotor function was evaluated until 6 weeks postinjury. Histological assessment of lesion volume and tissue sparing was performed at 6 weeks after SCI. Calpain inhibitor MDL28170 administered as a single postinjury i.v. bolus (20 mg/kg) or as a daily i.p. dose (1 mg/kg) improved locomotor function, but did not increase tissue sparing. Combined i.v. and daily i.p. MDL28170 administration resulted in significant improvement in both functional and pathological outcome measures, supporting the calpain theory of SCI proposed by Dr. Banik and colleagues.

Cytoplasmic extracts from adipose tissue stromal cells alleviates secondary damage by modulating apoptosis and promotes functional recovery following spinal cord injury

Spinal cord injury (SCI) typically results from sustained trauma to the spinal cord, resulting in loss of neurologic function at the level of the injury. However, activation of various physiological mechanisms secondary to the initial trauma including edema, inflammation, excito-toxicity, excessive cytokine release and apoptosis may exacerbate the injury and/or retard natural repair mechanisms. Herein, we demonstrate that cytoplasmic extracts prepared from adipose tissue stromal cells (ATSCs) inhibits H(2)O(2)-mediated apoptosis of cultured spinal cord-derived neural progenitor cells (NPCs) resulting in increased cell survival. The ATSC extracts mediated this effect by decreasing caspase-3 and c-Jun-NH2-terminal kinase (SAPK/JNK) activity, inhibiting cytochrome c release from mitochondria and reducing Bax expression levels in cells. Direct injection of ATSC extracts mixed with Matrigel into the spinal cord immediately after SCI also resulted in reduced apoptotic cell death, astrogliosis and hypo-myelination but did not reduce the extent of microglia infiltration. Moreover, animals injected with the ATSC extract showed significant functional improvement of hind limbs as measured by the BBB (Basso, Beattie and Bresnahan) scale. Collectively, these studies show a prominent therapeutic effect of ATSC cytoplasmic extracts on SCI principally caused by an inhibition of apoptosis-mediated cell death, which spares white matter, oligodendrocytes and neurons at the site of injury. The ability of ATSC extracts to prevent secondary pathological events and improve neurologic function after SCI suggests that extracts prepared from autologous cells harvested from SCI patients may have clinical utility.

Age-related differences in the local cellular and molecular responses to injury in developing spinal cord of the opossum, Monodelphis domestica

Immature spinal cord, unlike adult, has an ability to repair itself following injury. Evidence for regeneration, structural repair and development of substantially normal locomotor behaviour comes from studies of marsupials due to their immaturity at birth. We have compared morphological, cellular and molecular changes in spinal cords transected at postnatal day (P)7 or P14, from 3 h to 2 weeks post-injury, in South American opossums (Monodelphis domestica). A bridge between severed ends of cords was apparent 5 days post-injury in P7 cords, compared to 2 weeks in P14. The volume of neurofilament (axonal) material in the bridge 2 weeks after injury was 30% of control in P7- but < 10% in P14-injured cords. Granulocytes accumulated at the site of injury earlier (3 h) in P7 than in P14 (24 h)-injured animals. Monocytes accumulated 24 h post-injury and accumulation was greater in P14 cords. Accumulation of GFAP-positive astrocytes at the lesion occurred earlier in P14-injured cords. Neurites and growth cones were identified ultrastructurally in contact with astrocytes forming the bridge. Results using mouse inflammatory gene arrays showed differences in levels of expression of many TGF, TNF, cytokine, chemokine and interleukin gene families. Most of the genes identified were up-regulated to a greater extent following injury at P7. Some changes were validated and quantified by RT-PCR. Overall, the results suggest that at least some of the greater ability to recover from spinal cord transection at P7 compared to P14 in opossums is due to differences in inflammatory cellular and molecular responses.

Restoring function after spinal cord injury: promoting spontaneous regeneration with stem cells and activity-based therapies

Although neural regeneration is an active research field today, no current treatments can aid regeneration after spinal cord injury. This article reviews the feasibility of spinal cord repair and provides an overview of the range of strategies scientists are taking toward regeneration. The major focus of this article is the future role of stem cell transplantation and similar rehabilitative restorative approaches designed to optimize spontaneous regeneration by mobilizing endogenous stem cells and facilitating other cellular mechanisms of regeneration, such as axonal growth and myelination.

Contusion, dislocation, and distraction: primary hemorrhage and membrane permeability in distinct mechanisms of spinal cord injury

Object

In experimental models of spinal cord injury (SCI) researchers have typically focused on contusion and transection injuries. Clinically, however, other injury mechanisms such as fracture–dislocation and distraction also frequently occur. The objective of the present study was to compare the primary damage in three clinically relevant animal models of SCI.

Methods

Contusion, fracture–dislocation, and flexion–distraction animal models of SCI were developed. To visualize traumatic increases in cellular membrane permeability, fluorescein–dextran was infused into the cerebrospi-nal fluid prior to injury. High-speed injuries (approaching 100 cm/second) were produced in the cervical spine of deeply anesthetized Sprague–Dawley rats (28 SCI and eight sham treated) with a novel multimechanism SCI test system. The animals were killed immediately thereafter so that the authors could characterize the primary injury in the gray and white matter.

Sections stained with H & E showed that contusion and dislocation injuries resulted in similar central damage to the gray matter vasculature whereas no overt hemorrhage was detected following distraction. Contusion resulted in membrane disruption of neuronal somata and axons localized within 1 mm of the lesion epicenter. In contrast, membrane compromise in the dislocation and distraction models was observed to extend rostrally up to 5 mm, particularly in the ventral and lateral white matter tracts.

Conclusions

Given the pivotal nature of hemorrhagic necrosis and plasma membrane compromise in the initiation of downstream SCI pathomechanisms, the aforementioned differences suggest the presence of mechanism-specific injury regions, which may alter future clinical treatment paradigms.

Olfactory ensheathing cell transplantation as a strategy for spinal cord repair—what can it achieve?

Restoring function to the injured spinal cord represents one of the most formidable challenges in regenerative medicine. Glial cell transplantation is widely considered to be one of the most promising therapeutic strategies, and several differentiated glial cell types-in particular, Schwann cells and olfactory ensheathing cells (OECs)-have been proposed as transplant candidates. In this Review, we analyze evidence from animal studies for improved functional recovery following transplantation of OECs into spinal cord injuries, and examine the mechanisms by which repair might be achieved. Data obtained using various injury models support the view that OEC transplants can promote functional recovery, but accumulating anatomical evidence indicates that although axons regenerate within a transplant, they do not cross the lesion or reconnect with neurons on the opposite side to any significant extent. Consequently, it is possible that neuroprotection and promotion of sprouting from intact fibers are the main mechanisms that contribute to functional recovery. We conclude that for the foreseeable future the clinical benefits of OEC transplants alone are likely to be modest. The future potential of cell transplantation strategies will probably depend on the success with which the transplants can be combined with other, synergistic, therapies to achieve significant regeneration of axons and re-establish functionally useful connections across a spinal cord injury.

In SilicoModeling of Axonal Reconnection within A Discrete Fiber Tract after Spinal Cord Injury

Following spinal cord injury (SCI), descending axons that carry motor commands from the brain to the spinal cord are injured or transected, producing chronic motor dysfunction and paralysis. Reconnection of these axons is a major prerequisite for restoration of function after SCI. Thus far, only modest gains in motor function have been achieved experimentally or in the clinic after SCI, identifying the practical limitations of current treatment approaches. In this paper, we use an ordinary differential equation (ODE) to simulate the relative and synergistic contributions of several experimentally-established biological factors related to inhibition or promotion of axonal repair and restoration of function after SCI. The factors were mathematically modeled by the ODE. The results of our simulation show that in a model system, many factors influenced the achievability of axonal reconnection. Certain factors more strongly affected axonal reconnection in isolation, and some factors interacted in a synergistic fashion to produce further improvements in axonal reconnection. Our data suggest that mathematical modeling may be useful in evaluating the complex interactions of discrete therapeutic factors not possible in experimental preparations, and highlight the benefit of a combinatorial therapeutic approach focused on promoting axonal sprouting, attraction of cut ends, and removal of growth inhibition for achieving axonal reconnection. Predictions of this simulation may be of utility in guiding future experiments aimed at restoring function after SCI.

6-Shogaol, a natural product, reduces cell death and restores motor function in rat spinal cord injury

Spinal cord injury (SCI) results in progressive waves of secondary injuries, which via the activation of a barrage of noxious pathological mechanisms exacerbate the injury to the spinal cord. Secondary injuries are associated with edema, inflammation, excitotoxicity, excessive cytokine release, caspase activation and cell apoptosis. This study was aimed at investigating the possible neuroprotective effects of 6-shogaol purified from Zingiber officinale by comparing an experimental SCI rat group with SCI control rats. Shogaol attenuated apoptotic cell death, including poly(ADP-ribose) polymerase activity, and reduced astrogliosis and hypomyelination which occurs in areas of active cell death in the spinal cords of SCI rats. The foremost protective effect of shogaol in SCI would therefore be manifested in the suppression of the acute secondary apoptotic cell death. However, it does not attenuate active microglia and macrophage infiltration. This finding is supported by a lack of histopathological changes in the areas of the lesion in the shogaol-treated SCI rats. Moreover, shogaol-mediated neuroprotection has been linked with shogaol's attenuation of p38 mitogen-activated protein kinase, p-SAPK/JNK and signal transducer, and with transcription-3 activation. Our results demonstrate that shogaol administrated immediately after SCI significantly diminishes functional deficits. The shogaol-treated group recovered hindlimb reflexes more rapidly and a higher percentage of these rats regained responses compared with the untreated injured rats. The overall hindlimb functional improvement of hindlimbs, as measured by the Basso, Beattie and Bresnahan scale, was significantly enhanced in the shogaol-treated group relative to the SCI control rats. Our data show that the therapeutic outcome of shogaol probably results from its comprehensive effects of blocking apoptotic cell death, resulting in the protection of white matter, oligodendrocytes and neurons, and inhibiting astrogliosis. Our finding that the administration of shogaol prevents secondary pathological events in traumatic SCIs and promotes recovery of motor functions in an animal model raises the issue of whether shogaol could be used therapeutically in humans after SCI.

International spinal research trust research strategy. III: A discussion document

STUDY DESIGN

Discussion document.

OBJECTIVES/METHODS

To review the Research Strategy of the International Spinal Research Trust (ISRT), which identifies key areas of basic and clinical research that are likely to be beneficial in developing potential treatments for spinal cord injury for funding. This strategy is intended to both guide the programme of research towards areas of priority and stimulate discussion of the different avenues of research. This latest document has been developed to take into account the scientific progress in the 6 years since publication of the previous Research Strategy.

RESULTS/DISCUSSION

The latest scientific developments in research designed to repair the spinal cord and restore function following injury and how they might impact on spinal cord injury research are highlighted.

Demyelination and remyelination after spinal cord injury

Since the discovery in the 1960s that remyelination can occur in the damaged central nervous system (CNS) (Bunge et al. 1961), there has been much progress in understanding the cellular and molecular biology of oligodendroglia and the factors that regulate their propagation, migration, differentiation, maturation, and ability to myelinate nerve axons. More recently, greater understanding of disease states and the role of oligodendrocytes in remyelination have sparked tremendous interest in this once obscure field. Although the explosion of information is being hampered by adherence to commonly held beliefs based on empirical evidence, novel molecular and cellular tools are allowing scientists to address age-old assumptions. It is now recognized that, as well as promoting salutatory conduction along axons, oligodendroglia are important near-term clinical targets for restoring function after CNS injury, particularly spinal cord injury. Thus, remyelination appears to be one of the most feasible restoration strategies. This review focuses on concepts that are important for developing strategies of repair. The brightest young scientists will be attracted into this exciting field by its near-term potential for human application.

Strategies of medical intervention in the management of acute spinal cord injury

STUDY DESIGN

: Literature review.

OBJECTIVE

: The purpose of this paper is to review clinical treatment strategies and future developments in the treatment of acute spinal cord injury.

SUMMARY OF BACKGROUND DATA

: The treatment of acute spinal cord injury continues to be supportive. The search for specialized pharmacologic agents to prevent secondary injury and promote repair or regeneration remains heated.

METHODS

: Medline search from 1996 to present limited to clinical research and basic science review articles in the English Language.

RESULTS

: Steroids continue to be administered in the clinical setting of acute spinal cord injury primarily out of peer pressure and fear of litigation. Basic science experiments suggest that modulation of post-traumatic inflammation may provide the best opportunity to arrest the secondary injury cascade. Protein kinase and metalloproteinase inhibition are promising treatment strategies. Regeneration techniques are concentrating on cell transplantation and manipulating glial receptors and protein production. Clinical investigations are limited to Phase III trials on a very select few of these drugs.

CONCLUSIONS

: While many advances in the basic science of spinal cord injury provide optimism for future treatments, clinical science lags. At present, there are no pharmacologic strategies of proven benefit. Although steroids continue to be given to patients with spinal cord injury in many institutions, evidence of deleterious effects continues to accumulate. Current standard of care management includes support of arterial oxygenation and spinal cord perfusion pressure.

Respiratory abnormalities resulting from midcervical spinal cord injury and their reversal by serotonin 1A agonists in conscious rats

Respiratory dysfunction after cervical spinal cord injury (SCI) has not been examined experimentally using conscious animals, although clinical SCI most frequently occurs in midcervical segments. Here, we report a C5 hemicontusion SCI model in rats with abnormalities that emulate human post-SCI pathophysiology, including spontaneous recovery processes. Post-C5 SCI rats demonstrated deficits in minute ventilation (Ve) responses to a 7% CO2 challenge that correlated significantly with lesion severities (no injury or 12.5, 25, or 50 mm x 10 g weight drop; New York University impactor; p < 0.001) and ipsilateral motor neuron loss (p = 0.016). Importantly, C5 SCI resulted in at least 4 weeks of respiratory abnormalities that ultimately recovered afterward. Because serotonin is involved in respiration-related neuroplasticity, we investigated the impact of activating 5-HT1A receptors on post-C5 SCI respiratory dysfunction. Treatment with the 5-HT1A agonist 8-hydroxy-2-(di-n-propylmino)tetralin (8-OH DPAT) (250 microg/kg, i.p.) restored hypercapnic Ve at 2 and 4 weeks after injury (i.e., approximately 39.2% increase vs post-SCI baseline; p < or = 0.033). Improvements in hypercapnic Ve response after single administration of 8-OH DPAT were dose dependent and lasted for approximately 4 h(p < or = 0.038 and p < or = 0.024, respectively). Treatment with another 5-HT1A receptor agonist, buspirone (1.5 mg/kg, i.p.), replicated the results, whereas pretreatment with a 5-HT1A-specific antagonist, 4-iodo-N-[2-[4(methoxyphenyl)-1-piperazinyl]ethyl]-N-2-pyridinyl-benzamide (3 mg/kg, i.p.) given 20 min before 8-OH DPAT negated the effect of 8-OH DPAT. These results imply a potential clinical use of 5-HT1A agonists for post-SCI respiratory disorders.

Human embryonic stem cell-derived oligodendrocyte progenitor cell transplants remyelinate and restore locomotion after spinal cord injury

Demyelination contributes to loss of function after spinal cord injury, and thus a potential therapeutic strategy involves replacing myelin-forming cells. Here, we show that transplantation of human embryonic stem cell (hESC)-derived oligodendrocyte progenitor cells (OPCs) into adult rat spinal cord injuries enhances remyelination and promotes improvement of motor function. OPCs were injected 7 d or 10 months after injury. In both cases, transplanted cells survived, redistributed over short distances, and differentiated into oligodendrocytes. Animals that received OPCs 7 d after injury exhibited enhanced remyelination and substantially improved locomotor ability. In contrast, when OPCs were transplanted 10 months after injury, there was no enhanced remyelination or locomotor recovery. These studies document the feasibility of predifferentiating hESCs into functional OPCs and demonstrate their therapeutic potential at early time points after spinal cord injury.

Experimental strategies to promote spinal cord regeneration--an integrative perspective

Detailed pathophysiological findings of secondary damage phenomena after spinal cord injury (SCI) as well as the identification of inhibitory and neurotrophic proteins have yielded a plethora of experimental therapeutic approaches. Main targets are (i) to minimize secondary damage progression (neuroprotection), (ii) to foster axon conduction (neurorestoration) and (iii) to supply a permissive environment to promote axonal sprouting (neuroregenerative therapies). Pre-clinical studies have raised hope in functional recovery through the antagonism of growth inhibitors, application of growth factors, cell transplantation, and vaccination strategies. To date, even though based on successful pre-clinical animal studies, results of clinical trials are characterized by dampened effects attributable to difficulties in the study design (patient heterogeneity) and species differences. A combination of complementary therapeutic strategies might be considered pre-requisite for future synergistic approaches. Here, we line out pre-clinical interventions resulting in improved functional neurological outcome after spinal cord injury and track them on their intended way to bedside.

Functional recovery in traumatic spinal cord injury after transplantation of multineurotrophin-expressing glial-restricted precursor cells

Demyelination contributes to the physiological and behavioral deficits after contusive spinal cord injury (SCI). Therefore, remyelination may be an important strategy to facilitate repair after SCI. We show here that rat embryonic day 14 spinal cord-derived glial-restricted precursor cells (GRPs), which differentiate into both oligodendrocytes and astrocytes, formed normal-appearing central myelin around axons of cultured DRG neurons and had enhanced proliferation and survival in the presence of neurotrophin 3 (NT3) and brain-derived neurotrophin factor (BDNF). We infected GRPs with retroviruses expressing the multineurotrophin D15A (with both BDNF and NT3 activities) and then transplanted them into the contused adult thoracic spinal cord at 9 d after injury. Expression of D15A in the injured spinal cord is five times higher in animals receiving D15A-GRP grafts than ones receiving enhanced green fluorescent protein (EGFP)-GRP or DMEM grafts. Six weeks after transplantation, the grafted GRPs differentiated into mature oligodendrocytes expressing both myelin basic protein (MBP) and adenomatus polyposis coli (APC). Ultrastructural analysis showed that the grafted GRPs formed morphologically normal-appearing myelin sheaths around the axons in the ventrolateral funiculus (VLF) of spinal cord. Expression of D15A significantly increased the percentage of APC+ oligodendrocytes of grafted GRPs (15-30%). Most importantly, 8 of 12 rats receiving grafts of D15A-GRPs recovered transcranial magnetic motor-evoked potential responses, indicating that conduction through the demyelinated VLF axons was restored. Such electrophysiological recovery was not observed in rats receiving grafts of EGFP-GRPs, D15A-NIH3T3 cells, or an injection of an adenovirus expressing D15A. Recovery of hindlimb locomotor function was also significantly enhanced only in the D15A-GRP-grafted animals at 4 and 5 weeks after transplantation. Therefore, combined treatment with neurotrophins and GRP grafts can facilitate functional recovery after traumatic SCI and may prove to be a useful therapeutic strategy to repair the injured spinal cord.

Combined delivery of neurotrophin-3 and NMDA receptors 2D subunit strengthens synaptic transmission in contused and staggered double hemisected spinal cord of neonatal rat

We investigated whether administration of neurotrophin-3 (NT-3) and NMDA-2D-expressing units, found previously to enhance transmission in neonatal rat spinal cord, strengthens synaptic connections in the injured neonatal cord. We employed electrophysiological methods to evaluate the strength of synaptic transmission to individual motoneurons in the contusion and staggered double hemisection spinal cord injury (SCI) models. SCI at caudal thoracic levels (T11-T12) was carried out at postnatal day 2 (P2). Plugs containing NT-3- secreting fibroblasts and NR2D-expressing HSV-1 amplicons (HSVnr2d) were implanted above the lesion. Control animals were treated with an amplicon-expressing beta-galactosidase (HSVlac). After 8-10 days of treatment, the rats were sacrificed and spinal cords were removed for intracellular recording. Untreated contused cords preserved a fraction of white matter and weak monosynaptic responses were observed through the injury region. However, no synaptic connections were observed in control cords receiving double hemisection injury. Combined treatment with NT-3 and HSVnr2d strengthened monosynaptic connections in contused cords and induced the appearance of weak but functional multisynaptic connections in double hemisected cords. In contrast, treatment with either NT-3 or HSVnr2d alone failed to induce appearance of synaptic responses through the hemisected region. These results suggest that chronic treatment with NT-3 secreting fibroblasts combined with facilitated function of NMDA receptors by HSVnr2d treatment strengthens connections that survive incomplete SCI and therefore that such combined treatment might facilitate recovery of function following SCI.

Locomotor Deficits and Adaptive Mechanisms after Thoracic Spinal Cord Contusion in the Adult Rat

The rat is widely used for modeling human spinal cord injury (SCI) and paraplegia. However, quadruped animals adapt trunk, forelimb and hindlimb movements to compensate for deficits, improving their behavioral scores and complicating the interpretation of spontaneous and treatment-induced function recovery. The kinematics of locomotion was studied in rats, both normal and after SCI (T9 contusion), and variables indicative of hindlimb function were related to brain-spinal cord connections (BSCC) spared during lesioning. Normal animals showed forward velocities characteristic of fast walking. The hind paw was placed approximately three centimeters in front of the hip at the initial contact. Hip height decreased during the first third of hindlimb stance and increased later. Mild and moderate spinal cord contusions destroyed the gray matter and adjacent axons but spared the ventrolateral tracts to various degrees. Injured animals placed the hindpaw in a more caudal position than normal and showed reduced forward velocity and hip height. Knee extension was also impaired, and both hindlimb and forelimb steps were adapted to compensate for the deficits. BSCC was estimated by averaging the transverse area of white matter at the lesion epicenter and the percentage of brain neurons labeled after peroxidase injection into L2 and L3. Recovery of hindlimb motor function was proportional to the amount of BSCC. On average, injured animals retained 18% of BSSC and recovered 23% of hindlimb function. These findings show that kinematic analysis is a reliable tool for assessing locomotor deficits and compensations and suggest limited spontaneous motor plasticity after SCI.

Apoptotic cell death following traumatic injury to the central nervous system

Apoptotic cell death is a fundamental and highly regulated biological process in which a cell is instructed to actively participate in its own demise. This process of cellular suicide is activated by developmental and environmental cues and normally plays an essential role in eliminating superfluous, damaged, and senescent cells of many tissue types. In recent years, a number of experimental studies have provided evidence of widespread neuronal and glial apoptosis following injury to the central nervous system (CNS). These studies indicate that injury-induced apoptosis can be detected from hours to days following injury and may contribute to neurological dysfunction. Given these findings, understanding the biochemical signaling events controlling apoptosis is a first step towards developing therapeutic agents that target this cell death process. This review will focus on molecular cell death pathways that are responsible for generating the apoptotic phenotype. It will also summarize what is currently known about the apoptotic signals that are activated in the injured CNS, and what potential strategies might be pursued to reduce this cell death process as a means to promote functional recovery.

The therapeutic window for spinal cord decompression in a rat spinal cord injury model

OBJECT

There are no clinically based guidelines to direct the spine surgeon as to the proper timing to undertake decompression after spinal cord injury (SCI) in patients with concomitant stenosis-induced cord compression. The following three factors affect the prognosis: (1) severity of SCI; (2) degree of extrinsic spinal cord compression; and (3) duration of spinal cord compression.

METHODS

To elucidate further the relationship between varying degrees of spinal stenosis and a mild contusion-induced SCI (6.25 g-cm), a rat SCI/stenosis model was developed in which 1.13- and 1.24-mm-thick spacers were placed at T-10 to create 38 and 43% spinal stenosis, respectively. Spinal cord damage was observed after the stenosis-SCI that was directly proportional to the duration of spinal cord compression. The therapeutic window prior to decompression was 6 and 12 hours in the 43 and 38% stenosis-SCI lesions, respectively, to maintain locomotor activity. A significant difference in total lesion volume was observed between the 2-hour and the delayed time(s) to decompression (38% stenosis-SCI, 12 and 24 hours, p < 0.05; 43% stenosis-SCI, 24 hours, p < 0.05) indicating a more favorable neurological outcome when earlier decompression is undertaken. This finding was further supported by the animal's ability to support weight when decompression was performed by 6 or 12 hours compared with 24 hours after SCI.

CONCLUSIONS

Analysis of the findings in this study suggests that early decompression in the rat improves locomotor function. Prolongation of the time to decompression may result in irreversible damage that prevents locomotor recovery.

Strategies to promote neural repair and regeneration after spinal cord injury

STUDY DESIGN

Retrospective review of current literature regarding neuroprotection and axonal regeneration therapies for acute spinal cord injury.

OBJECTIVES

To provide an update for spine clinicians of the emerging therapeutic strategies for promoting neural repair and regeneration after spinal cord injury.

SUMMARY OF BACKGROUND DATA

The neuroscientific community has generated a number of novel potential treatments for spinal injuries, some of which have entered clinical trials. Clinicians who manage spinal cord trauma are likely to encounter patients and their families who have questions or wish to be involved in these emerging treatments.

METHODS

Literature review, with particular focus on currently used medications that may have neuroprotective potential in spinal cord injury, and axonal regeneration strategies that are emerging in preliminary human clinical trials.

RESULTS

A number of medications such as erythropoietin and minocycline have demonstrated neuroprotective properties in animal models of spinal cord injury, and their long-established safety in humans make them appealing candidates for clinical trials. Human experience with novel neuroprotective and axonal regeneration strategies is growing around the world, and the peer-reviewed reporting of this is anxiously awaited.

CONCLUSIONS

The initiation of human clinical trials for spinal cord-injured patients heralds great hope that effective therapies will be forthcoming, although a great deal remains to be learned. Clinicians must provide leadership in the epidemiologic design and rigor of these initial forays into human evaluation.

Generating chimeric spinal cord: a novel model for transplantable oligodendrocyte progenitors derived from embryonic stem cells

Object

To identify and evaluate stem cell–derived oligodendrocytes obtained for cell transplantation therapies, the authors developed a novel model to examine single, adult oligodendrocytes in situ.

Methods

Green fluorescent protein–expressing, mouse embryonic stem cells (ESCs) were neural induced and additionally staged in an oligosphere preparatory step for high-yield derivation of oligodendrocyte progenitors. These transplantable, induced progenitors were injected into postnatal Day 2 rat pups, in which spinal cord sections were then examined at 3 and 9 weeks posttransplantation.

Conclusions

Transplanted oligosphere ESCs survived and integrated anatomically into postnatal and adult white matter, generating targeted regions of chimeric spinal cord. A simple model for identifying adult oligodendrocytes in situ is presented, which is suitable for use in further studies examining functional myelination and derivation of oligodendrocytes from genetically engineered ESC lines, including human ESCs. Results from the model presented here demonstrate a unique method for examining transplantable oligodendrocyte progenitors derived from ESCs for repair of white matter disease.

Real-time quantitative PCR analysis of temporal-spatial alterations in gene expression after spinal cord contusion

Rat spinal cord contusion injury models the histopathology associated with much clinical spinal cord injury (SCI). Studies on altered gene expression after SCI in these models may identify therapeutic targets for reducing secondary injury after the initial trauma and/or enhancing recovery processes. However, complex spatial and temporal alterations after injury could complicate interpretation of changes in gene expression. To test this hypothesis, we selected six genes and studied their temporal and spatial patterns of expression at 1 h, 1, 3 and 7 days after a standardized spinal cord contusion produced by a weight drop device (10 g x 25 mm at T8). Real-time RT-PCR using TaqMan probes was employed to quantify mRNA for proteolipid protein, glyceraldehyde-3-phosphate dehydrogenase, glial fibrillary acidic protein, nestin, and the GluR2 and NR1 subunits of glutamate receptors. We found widely different temporal and spatial patterns of altered gene expression after SCI, including instances of opposing up- and down-regulation at different locations in tissue immediately adjacent to the injury site. We conclude that greater use of the reliable and extremely sensitive technique of quantitative real-time PCR for regional tissue analysis is important for understanding the altered gene expression that occurs after CNS trauma.

Cell proliferation and replacement following contusive spinal cord injury

After spinal cord injury (SCI), about 50% of the oligodendrocytes and astrocytes in the residual white matter at the injury site are lost by 24 h. However, chronically after SCI, the density of oligodendrocytes is normal. Previous studies have shown that the adult rat spinal cord contains a pool of proliferating glial progenitors whose progeny could help restore cell density after injury. To study proliferation in response to injury, we performed SCI on adult female rats at the T8 level, using a standardized contusion model. Animals received bromodeoxyuridine (BrdU) injections during the first week after SCI, and were perfused within 2 h for acute studies, and at 6 weeks for chronic studies. The tissue was analyzed using immunohistochemical detection of BrdU and cell marker antigens. We demonstrate that cell proliferation in the residual white matter is increased at 1-7 days after SCI, peaking on day 3. Dividing cells include oligodendrocytes, astrocytes, microglia/macrophages, and a high proportion of NG2(+) glial precursors. By 6 weeks, some cells that had been labeled 2-4 days after SCI were still present. Double immunohistochemistry showed that while very few of these cells expressed NG2 or the microglia/macrophage marker OX42, about 50% expressed CC1 or glial fibrillary acidic protein (GFAP), markers of mature oligodendrocytes and astrocytes, respectively. The post-injury environment represented by residual white matter is thus permissive to the differentiation of glial precursors. Cells that are stimulated to divide during the first week after SCI develop chronically into mature phenotypes that replace macroglia lost after injury.

From Animal Models to Humans

There are currently no fully restorative therapies for human spinal cord injury (SCI). Here,we briefly review the different types of human SCI pathology as well as the most commonly used rodent and nonhuman primate models of SCI that are used to simulate these pathologies and to test potential therapies. We then discuss various high profile (sometimes controversial) experimental strategies that have reported CNS axon regeneration and functional recovery of limb movement using these animal models of SCI. We particularly focus upon strategies that have been tested both in rodents and in nonhuman primates, and highlight those which are currently transitioning to clinical tests or trials in humans. Finally we discuss ways in which animal studies might be improved and what the future may hold for physical therapists involved in rehabilitation of humans with SCI.

Functional and electrophysiological changes after graded traumatic spinal cord injury in adult rat

A graded contusion spinal cord injury (SCI) was created in the adult rat spinal cord using the Infinite Horizons (IH) impactor to study the correlation between injury severity and anatomical, behavioral, and electrophysiological outcomes. Adult Fisher rats were equally divided into five groups and received contusion injuries at the ninth thoracic level (T9) with 100, 125, 150, 175, or 200 kdyn impact forces, respectively. Transcranial magnetic motor-evoked potentials (tcMMEPs) and BBB open-field locomotor analyses were performed weekly for 4 weeks postinjury. Our results demonstrated that hindlimb locomotor function decreased in accordance with an increase in injury severity. The locomotor deficits were proportional to the amount of damage to the ventral and lateral white matter (WM). Locomotor function was strongly correlated to the amount of spared WM, which contains the reticulospinal and propriospinal tracts. Normal tcMMEP latencies were recorded in control, all of 100-kdyn-injured and half of 125-kdyn-injured animals. Delayed latency responses were recorded in some of 125-kdyn-injured and all of 150-kdyn-injured animals. No tcMMEP responses were recorded in 175- and 200-kdyn-injured animals. Comparison of tcMMEP responses with areas of WM loss or demyelination identified the medial ventrolateral funiculus (VLF) as the location of the tcMMEP pathway. Immunohistochemical and electromicroscopic (EM) analyses showed the presence of demyelinated axons in WM tracts surrounding the lesion cavities at 28 days postinjury. These data support the notion that widespread WM damage in the ventral and lateral funiculi may be a major cause for locomotor deficits and lack of tcMMEP responses after SCI.

Tissue-engineering approaches for axonal guidance

Owing to the profound impact of nervous system damage, extensive studies have been carried out aimed at facilitating axonal regeneration following injury. Tissue engineering, as an emerging and rapidly growing field, has received extensive attention for nervous system axonal guidance. Numerous engineered substrates containing oriented extracellular matrix molecules, cells or channels have displayed potential of supporting axonal regeneration and functional recovery. Most attempts are focused on seeking new biomaterials, new cell sources, as well as novel designs of tissue-engineered neuronal bridging devices, to generate safer and more efficacious neuronal tissue repairs.

Spinal cord injury is accompanied by chronic progressive demyelination

Preceding the development of therapeutic strategies for spinal cord injury is an identification of those pathological processes that might serve as therapeutic targets. Although demyelination has been documented as a secondary degenerative component of spinal cord injury in several species including humans, the extent of demyelination and its functional consequence remain unknown. In this report, we document the extent of demyelination and remyelination up to 450 days following contusive spinal cord injury in adult rats. The overall number of demyelinated axons peaked at 1 day post injury, declined by 7-14 days post injury, and then progressively increased up to 450 days post injury. Oligodendrocyte and Schwann cell remyelinated axons appeared by 14 days post injury. Although remyelinated axons were present from 14 to 450 days post injury, remyelination was incomplete, as indicated by the presence of demyelinated axons at every time point examined. These studies demonstrate for the first time that spinal cord injury is accompanied by chronic progressive demyelination, and they substantiate demyelination as a target for therapeutic intervention.

Cellular transplantation strategies for spinal cord injury and translational neurobiology

Basic science advances in spinal cord injury and regeneration research have led to a variety of novel experimental therapeutics designed to promote functionally effective axonal regrowth and sprouting. Among these interventions are cell-based approaches involving transplantation of neural and non-neural tissue elements that have potential for restoring damaged neural pathways or reconstructing intraspinal synaptic circuitries by either regeneration or neuronal/glial replacement. Notably, some of these strategies (e.g., grafts of peripheral nerve tissue, olfactory ensheathing glia, activated macrophages, marrow stromal cells, myelin-forming oligodendrocyte precursors or stem cells, and fetal spinal cord tissue) have already been translated to the clinical arena, whereas others have imminent likelihood of bench-to-bedside application. Although this progress has generated considerable enthusiasm about treating what once was thought to be a totally incurable condition, there are many issues to be considered relative to treatment safety and efficacy. The following review reflects on different experimental applications of intraspinal transplantation with consideration of the underlying pathological, pathophysiological, functional, and neuroplastic responses to spinal trauma that such treatments may target along with related issues of procedural and biological safety. The discussion then moves to an overview of ongoing and completed clinical trials to date. The pros and cons of these endeavors are considered, as well as what has been learned from them. Attention is primarily directed at preclinical animal modeling and the importance of patterning clinical trials, as much as possible, according to laboratory experiences.

Sodium channel blockade with phenytoin protects spinal cord axons, enhances axonal conduction, and improves functional motor recovery after contusion SCI

Accumulation of intracellular sodium through voltage-gated sodium channels (VGSCs) is an important event in the cascade leading to anatomic degeneration of spinal cord axons and poor functional outcome following traumatic spinal cord injury (SCI). In this study, we hypothesized that phenytoin, a sodium channel blocker, would result in protection of axons with concomitant improvement of functional recovery after SCI. Adult male Sprague-Dawley rats underwent T9 contusion SCI after being fed normal chow or chow containing phenytoin; serum levels of phenytoin were within therapeutic range at the time of injury. At various timepoints after injury, quantitative assessment of lesion volumes, axonal degeneration, axonal conduction, and functional locomotor recovery were performed. When compared to controls, phenytoin-treated animals demonstrated reductions in the degree of destruction of gray and white matter surrounding the lesion epicenter, sparing of axons within the dorsal corticospinal tract (dCST) and dorsal column (DC) system rostral to the lesion site, and within the dorsolateral funiculus (DLF) caudal to the lesion site, and enhanced axonal conduction across the lesion site. Improved performance in measures of skilled locomotor function was observed in phenytoin-treated animals. Based on these results, we conclude that phenytoin provides neuroprotection and improves functional outcome after experimental SCI, and that it merits further examination as a potential treatment strategy in human SCI.

Morphometric analyses of axons in the human lateral corticospinal tract: cervical/lumbar level comparison and relation to the ageing process

Myelinated axons in the human lateral corticospinal tract (LCST) at the C6 and L4 levels were examined on 16 male cadavers, with age ranging from 41 to 88 years. The average area of axons in the LCST was measured using a microscopic image-analyzing system. Our data show that the average area of axons at the C6 and L4 levels decreased with age. We also noticed that the average area of axons was larger at the C6 level than at the L4 level in all cases. This decrease may be related to a parallel decrease of conduction velocity in the LCST during the ageing process.

Degenerative and regenerative mechanisms governing spinal cord injury

Spinal cord injury (SCI) is a major cause of disability, and at present, there is no universally accepted treatment. The functional decline following SCI is contributed to both direct mechanical injury and secondary pathophysiological mechanisms that are induced by the initial trauma. These mechanisms initially involve widespread haemorrhage at the site of injury and necrosis of central nervous system (CNS) cellular components. At later stages of injury, the cord is observed to display reactive gliosis. The actions of astrocytes as well as numerous other cells in this response create an environment that is highly nonpermissive to axonal regrowth. Also manifesting important effects is the immune system. The early recruitment of neutrophils and at later stages, macrophages to the site of insult cause exacerbation of injury. However, at more chronic stages, macrophages and recruited T helper cells may potentially be helpful by providing trophic support for neuronal and non-neuronal components of the injured CNS. Within this sea of injurious mechanisms, the oligodendrocytes appear to be highly vulnerable. At chronic stages of SCI, a large number of oligodendrocytes undergo apoptosis at sites that are distant to the vicinity of primary injury. This leads to denudement of axons and deterioration of their conductive abilities, which adds significantly to functional decline. By indulging into the molecular mechanisms that cause oligodendrocyte apoptosis and identifying potential targets for therapeutic intervention, the prevention of this apoptotic wave will be of tremendous value to individuals living with SCI.