Robust axonal growth and a blunted macrophage response are associated with impaired functional recovery after spinal cord injury in the MRL/MpJ mouse.

Spinal cord injury (SCI) in mammals leads to a robust inflammatory response followed by the formation of a glial and connective tissue scar that comprises a barrier to axonal regeneration. The inbred MRL/MpJ mouse strain exhibits reduced inflammation after peripheral injury and shows true regeneration without tissue scar formation following an ear punch wound. We hypothesized that following SCI, the unique genetic wound healing traits of this strain would result in reduced glial and connective tissue scar formation, increased axonal growth, and improved functional recovery. Adult MRL/MpJ and C57BL/6J mice were subjected to a mid-thoracic spinal contusion and the distribution of axon profiles and selected cellular and extracellular matrix components was compared at 1, 2, 4 and 6 weeks post-injury. Recovery of hind-limb locomotor function was assessed over the same time period. The MRL/MpJ mice exhibited robust axon growth within the lesion, beginning at 4 weeks post-injury. This growth was accompanied by reduced macrophage staining at 1, 2, 4 and 6 weeks post-injury, decreased chondroitin sulfate proteoglycan staining at 1-2 weeks and increased laminin staining throughout the lesion at 2-6 weeks post-injury. Paradoxically, the extent of locomotor recovery was impaired in the MRL/MpJ mice. Close examination of the chronic lesion site revealed evidence of ongoing degeneration both within and surrounding the lesion site. Thus, the regenerative genetic wound healing traits of the MRL/MpJ mice contribute to the evolution of a lesion environment that supports enhanced axon growth after SCI. However, this response occurs at the expense of meaningful functional recovery.

Constraints on cosmic neutrino fluxes from the Antarctic Impulsive Transient Antenna experiment.

We report new limits on cosmic neutrino fluxes from the test flight of the Antarctic Impulsive Transient Antenna (ANITA) experiment, which completed an 18.4 day flight of a prototype long-duration balloon payload, called ANITA-lite, in early 2004. We search for impulsive events that could be associated with ultrahigh energy neutrino interactions in the ice and derive limits that constrain several models for ultrahigh energy neutrino fluxes and rule out the long-standing -burst model.

Experimental modelling of human spinal cord injury: a model that crosses the species barrier and mimics the spectrum of human cytopathology.

STUDY DESIGN: Literature review and presentation of an experimental model of human spinal cord injury, (SCI). OBJECTIVES: Experimental designs seek to mimic and model the physical processes by which human SCI occurs and replicate the variety of chronic pathologies that characterize its long term effects. The variations in biological processes that are present between species have contributed to recent difficulties in generalizing experimental findings to the human condition. In this review, one finds: (1) a discourse on the pathological nature of the chronic human lesion, (2) a consideration of how the physical properties of soft tissue injury result in acute and chronic changes in the spinal substance, (3) a description of a device (ESCID) that is able to replicate and dynamically monitor physical indices of SCI as they take place in experimental models, and (4) a summary of how use of this device in different species has allowed the biomechanical descriptors of such injuries to be easily compared even in murine models. SETTING: Ohio State University, Ohio, USA. RESULTS: Careful attention to the details of injury device design has finally allowed a direct comparison of contusion-type injury models in the rat and mouse. Biomechanical outcomes with predictive capabilities have evolved that allow the investigator to create the range of pathologies seen in the human lesion even in these small vertebrates. The predictive cytopathology and our ability to manipulate the mouse genome will allow the testing of specific hypotheses related to cause and effect in experimental spinal cord injuries. Since the biomechanics, pathology, and chronic outcomes appear to be similar to those seen in the human, these animal models should facilitate rapid progress in the design of human therapeutics. CONCLUSIONS: Biomechanics of certain elements of experimental spinal injury are surprisingly accurate descriptors of acute and chronic pathologies in the spinal cord. This tenet applies across species and has often allowed more accurate design of clinical trials in the past few decades. As molecular approaches to this problem evolve, the use of species with known genomes appear warranted. Models that take advantage of these approaches are likely to produce innovations that quicken the pace of human trial strategies.

Pegylated brain-derived neurotrophic factor shows improved distribution into the spinal cord and stimulates locomotor activity and morphological changes after injury.

The neurotrophin brain-derived neurotrophic factor (BDNF) shows promise for the treatment of central nervous system (CNS) trauma and disease. Effective delivery methods are required, however, for BDNF to be useful as a therapeutic agent. To this end, we examined the penetration of intrathecally infused N-terminal pegylated BDNF (peg-BDNF) compared to similar infusion of native BDNF after spinal cord injury (SCI). Pegylation dramatically improved delivery of BDNF to the spinal cord and induced the expression of Fos in spinal cord neurons. To test whether enhanced delivery would improve the modest effects on behavioral recovery and axonal outgrowth observed with native BDNF infusion, we assessed the efficacy of 2-week 25 microg/day peg-BDNF treatment, beginning 12-24 h (early) or 15 days (delayed) after midthoracic spinal contusion. Similar to native BDNF, early treatment with peg-BDNF accelerated the recovery of stepping in the open-field and acutely stimulated locomotor central pattern generator activity, as seen by the activation of hindlimb airstepping during either period of administration. The infusion of peg-BDNF, regardless of the timing of delivery, was related to enhanced sprouting of putative cholinergic fibers, like that observed after high dose native BDNF treatment. Despite improved delivery, however, neither axonal responses nor the extent of locomotor recovery were enhanced compared to native BDNF treatment. This suggests that alternative strategies, such as neurotrophin treatment in conjunction with cell transplantation techniques, or treatment nearer the cell bodies of target neurons might be employed in an attempt to effect significant repair after SCI.

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.

Proliferation of NG2-positive cells and altered oligodendrocyte numbers in the contused rat spinal cord.

Given the numerous reparative roles glia may play after spinal cord injury (SCI), glial proliferation and cell number were examined in a model of traumatic SCI. Emphasis was placed on analysis of oligodendrocytes and NG2-positive (NG2+) cells, an endogenous cell population that may be involved in oligodendrocyte replacement. Overall, proliferation (assessed by bromodeoxyuridine incorporation) was markedly elevated during the first 2 weeks after injury and declined thereafter; a large portion of these dividing cells likely consisted of microglia-macrophages. Although the total number of NG2+ cells in the epicenter was reduced by half, we noted protracted proliferation in surviving NG2+ cells, with values sevenfold greater than in uninjured controls. Elevated proliferation of NG2+ cells persisted throughout the first 4 weeks after injury. However, the absolute number of NG2+ cells was not increased over controls, suggesting that the daughter cells either did not survive or they differentiated into other cell types. As expected, oligodendrocyte numbers were drastically altered after SCI. By 7 d after injury, the number of oligodendrocytes at the impact site was reduced by 93%. Despite ongoing tissue loss, the number of oligodendrocytes in spared tissue rose threefold at 14 d after injury. Although the function of NG2+ cells within the spinal cord is not completely understood, several studies suggest that they may differentiate into oligodendrocytes. Thus, proliferating NG2+ cells may contribute to the increased oligodendrocyte number observed at 2 weeks after injury. Future studies are required, however, to definitively determine the role NG2+ cells play in oligodendrocyte genesis, remyelination, and other post-injury events.

Traumatic spinal cord injury produced by controlled contusion in mouse.

Previous work from this laboratory has described a rat spinal cord injury (SCI) model in which the mid-thoracic spinal cord is subjected to a single rapid and calibrated displacement at the site of a dorsal laminectomy. Injury is initiated at the tip of a vertical shaft driven by an electromagnetic shaker. Transducers arranged in series with the shaft record the patterns of displacement and force during the impact sequence. In the present study, this device and the relevant surgical procedures were adapted to produce a spinal contusion injury model in laboratory mice. The signal generator for the injury device has also been converted to a computer-controlled interface to permit extension of the model to other laboratories. Mice were subjected to SCI across a range of severities by varying the amplitude of displacement and the magnitude of measured preload force on the dural surface. A moderate injury produced by displacement of 0.5 mm over 25 msec resulted in initial paralysis and recovery of locomotion with chronic deficits in hindlimb function. The magnitude of the peak force, impulse, power, and energy generated at impact were correlated with behavioral outcome at 1 day postinjury, while peak displacement and impulse were the best predictors of behavioral outcome at 28 days postinjury. The shape of the force recording proved to be a highly sensitive measure of subtle variations in the spinal compartment that were otherwise difficult to detect in this small species. The results demonstrate that the electromagnetic spinal cord injury device (ESCID) can be used to produce a well-controlled contusion injury in mice. The unique features of controlled displacement and monitoring of the biomechanical parameters at the time of impact provide advantages of this model for reducing outcome variability. Use of this model in mice with naturally occurring and genetically engineered mutations will facilitate understanding of the molecular mechanisms of pathophysiology following traumatic spinal cord injury.

Localization of transforming growth factor-beta1 and receptor mRNA after experimental spinal cord injury.

Transforming growth factor-beta1 (TGFbeta1) is a cytokine/growth factor found within the pathological central nervous system. TGFbeta1 has been shown to inhibit the release of cytotoxic molecules from microglia and macrophages, decrease astrocyte proliferation, and promote neuron survival. Because of the relevance of these actions to spinal cord injury, we examined TGFbeta1 and its receptors betaRI and betaRII mRNA levels and localization within the contused rat spinal cord using in situ hybridization. At the lesion site, TGFbeta1 mRNA peaked at 7 days postinjury and declined thereafter. Temporal and spatial localization of the betaRI and betaRII receptor mRNA closely mimicked that for TGFbeta1 in the epicenter. TGFbeta1, betaRI, and betaRII mRNAs also were elevated rostral and caudal to the injury, especially in regions known to contain activated microglia and degenerating axon profiles. Immunohistochemical staining of nearby sections confirmed that the highest levels of TGFbeta1 and receptor mRNA corresponded to regions filled with activated microglia and macrophages. The similar expression pattern of TGFbeta1, betaRI, and betaRII mRNA within the injured spinal cord suggests a local site of action. Since TGFbeta1 can act as an immunosuppressant as well as a stimulant for growth factors and neurite sprouting, it likely plays an important role, both temporally and spatially, in orchestrating postinjury events within the spinal cord.

Mechanisms through which PDGF alters intracellular calcium levels in U-1242 MG human glioma cells.

PDGF-BB induces a rapid, sustained increase in intracellular calcium levels in U-1242 MG cells. We used several calcium channel blockers to identify the types of channels involved. L channel blockers (verapamil, nimodipine, nicardipine, nitrendipine and taicatoxin) had no effect on PDGF-BB induced alterations in intracellular calcium. Blockers of P, Q and N channels (omega-agatoxin-IVA, omega-conotoxin MVIIC and omega-conotoxin GVIA) also had no effect. This indicates that these channels play an insignificant role in supplying the Ca2+ necessary for PDGF stimulated events in U-1242 MG cells. However, a T channel blocker (NDGA) and the non-specific (NS) calcium channel blockers (FFA and SK&F 9365) abolished PDGF-induced increases in intracellular calcium. This indicates that PDGF causes calcium influx through both non-specific cationic channels and T channels. To study the participation of intracellular calcium stores in this process, we used thapsigargin, caffeine and ryanodine, all of which cause depletion of intracellular calcium stores. The PDGF effect was abolished using both thapsigargin and caffeine but not ryanodine. Collectively, these data indicate that in these human glioma cells PDGF-BB induces release of intracellular calcium from caffeine- and thapsigargin-sensitive calcium stores which in turn lead to further calcium influx through both NS and T channels.

Depletion of hematogenous macrophages promotes partial hindlimb recovery and neuroanatomical repair after experimental spinal cord injury.

Traumatic injury to the spinal cord initiates a series of destructive cellular processes which accentuate tissue damage at and beyond the original site of trauma. The cellular inflammatory response has been implicated as one mechanism of secondary degeneration. Of the various leukocytes present in the spinal cord after injury, macrophages predominate. Through the release of chemicals and enzymes involved in host defense, macrophages can damage neurons and glia. However, macrophages are also essential for the reconstruction of injured tissues. This apparent dichotomy in macrophage function is further complicated by the overlapping influences of resident microglial-derived macrophages and those phagocytes that are derived from peripheral sources. To clarify the role macrophages play in posttraumatic secondary degeneration, we selectively depleted peripheral macrophages in spinal-injured rats during a time when inflammation has been shown to be maximal. Standardized behavioral and neuropathological analyses (open-field locomotor function, morphometric analysis of the injured spinal cord) were used to evaluate the efficacy of this treatment. Beginning 24 h after injury and then again at days 3 and 6 postinjury, spinal cord-injured rats received intravenous injections of liposome-encapsulated clodronate to deplete peripheral macrophages. Within the spinal cords of rats treated in this fashion, macrophage infiltration was significantly reduced at the site of impact. These animals showed marked improvement in hindlimb usage during overground locomotion. Behavioral recovery was paralleled by a significant preservation of myelinated axons, decreased cavitation in the rostrocaudal axis of the spinal cord, and enhanced sprouting and/or regeneration of axons at the site of injury. These data implicate hematogenous (blood-derived) macrophages as effectors of acute secondary injury. Furthermore, given the selective nature of the depletion regimen and its proven efficacy when administered after injury, cell-specific immunomodulation may prove useful as an adjunct therapy after spinal cord injury.

Operant conditioning of H-reflex increase in spinal cord--injured rats.

Operant conditioning of the spinal stretch reflex or its electrical analog, the H-reflex, is a new model for exploring the mechanisms of long-term supraspinal control over spinal cord function. Primates and rats can gradually increase (HRup conditioning mode) or decrease (HRdown conditioning mode) the H-reflex when reward is based on H-reflex amplitude. An earlier study indicated that HRdown conditioning of the soleus H-reflex in rats is impaired following contusion injury to thoracic spinal cord. The extent of impairment was correlated with the percent of white matter lost at the injury site. The present study investigated the effects of spinal cord injury on HRup conditioning. Soleus H-reflexes were elicited and recorded with chronically implanted electrodes from 14 rats that had been subjected to calibrated contusion injuries to the spinal cord at T8. At the lesion epicenter, 12-39% of the white matter remained. After control-mode data were collected, each rat was exposed to the HRup conditioning mode for 50 days. Final H-reflex amplitudes after HRup conditioning averaged 112% (+/-22% SD) of control. This value was significantly smaller than that for 13 normal rats exposed to HRup conditioning, in which final amplitude averaged 153% (+/-51%) SD of control. As previously reported for HRdown conditioning after spinal cord injury, success was inversely correlated with the severity of the injury as assessed by white matter preservation and by time to return of bladder function. HRup and HRdown conditioning are similarly sensitive to injury. These results further demonstrate that H-reflex conditioning is a sensitive measure of the long-term effects of injury on supraspinal control over spinal cord functions and could prove a valuable measure of therapeutic efficacy.

Peroxynitrite production and activation of poly (adenosine diphosphate-ribose) synthetase in spinal cord injury.

Peroxynitrite formation and the subsequent activation of the nuclear enzyme, poly (adenosine diphosphate [ADP]-ribose) synthetase (PARS), has been implicated in the pathogenesis of several neurodegenerative disorders. Here, we demonstrate that nitrotyrosine, an indicator of peroxynitrite generation, and poly (ADP) ribose, a marker of PARS activation, were selectively localized within tissues from spinal cord-injured rats. Our data implicate a role for peroxynitrite production and PARS activation in the development of spinal cord trauma.

Assessment of the mechanism by which prolactin stimulates progesterone production by early corpora lutea of pigs.

Previously, we reported that administration of prolactin (PRL) during the early luteal phase in sows increases plasma progesterone concentrations. In the current study, we searched for the mechanisms by which PRL exerts this luteotrophic effect. The objectives of the study were (1) to examine the effect of PRL and/or low-density lipoproteins (LDL) on progesterone production by porcine luteal cells derived from early corpora lutea, and (2) to assess the ability of PRL to activate phosphoinositide-specific phospholipase C (PI-PLC) and protein kinase C (PKC) in these luteal cells. Ovaries with early corpora lutea (day 1-2 of the oestrous cycle) were obtained from the slaughterhouse. Progesterone production by dispersed luteal cells was measured after treatment with PRL, phorbol 12-myristate 13-acetate or inhibitors of PKC in the presence or absence of LDL. LDL increased progesterone concentration in the incubation medium (304.5 vs 178.6 ng/ml in control, P<0.05). PRL augmented LDL-stimulated progesterone secretion by luteal cells (to 416 ng/ml, P<0.05), but PRL alone did not affect progesterone production (209.6 ng/ml, P>0.05). Staurosporine, a PKC inhibitor, inhibited progesterone secretion stimulated by the combined action of LDL and PRL; however, such inhibition was not demonstrated when cells were treated with the PKC inhibitor, H-7. PKC activation was assessed by measuring the specific association of [H]phorbol dibutyrate (H-PDBu) with luteal cells after treatment with PRL or ionomycin (a positive control). PRL and ionomycin increased H-PDBu-specific binding in early luteal cells by 28+/-5.5% (within 5 min) and 70.2+/-19.3% (within 2 min) over control binding respectively (P<0.05). In addition, PRL did not augment the LDL-stimulated progesterone production in PKC-deficient cells. In contrast with PKC, total inositol phosphate accumulation, as well as intracellular free calcium concentrations, were not affected by PRL in the current study. We conclude that PRL, in the presence of LDL, stimulates progesterone production by early corpora lutea in vitro. Moreover, PRL appears to activate PKC, but not PI-PLC, in these cells. Thus intracellular transduction of the PRL signal may involve activation of PKC that is not dependent on PI-PLC.

Effect of neutrophil depletion in acute cerebritis.

Inhibition of the host's neutrophil response has been proposed as one means to reduce tissue damage in acute inflammation. If this approach can be applied in acute central nervous system (CNS) infection, the long-term morbidity, which occurs in CNS infection, might be reduced. Previous studies in models of CNS infection yielded conflicting results whether neutrophil depletion might be protective. To determine whether neutrophil depletion reduces tissue necrosis and cerebrovascular injury in experimental bacterial cerebritis, we depleted circulating neutrophils with an IgM monoclonal antibody, RP3, given after the start of the infection. RP3 treatment successfully depleted circulating neutrophils and reduced the extent of neutrophil influx into the cerebritis region. The extent of tissue necrosis, measured histologically, and the regional increase of blood-brain barrier (BBB) permeability were not inhibited by neutrophil depletion, and in animals treated with RP3 alone, the extent of tissue necrosis and BBB permeability tended to be larger than in S. aureus inoculated controls. We conclude that host neutrophils do not add to the tissue and cerebrovascular damage created by the intracerebral inoculation of a pathogenic bacteria, and the neutrophils serve to diminish local damage in the setting of a cerebritis.

Selective chemokine mRNA accumulation in the rat spinal cord after contusion injury.

Following traumatic injury to the spinal cord, hematogenous inflammatory cells including neutrophils, monocytes, and lymphocytes infiltrate the lesion in a distinct temporal sequence. To examine potential mechanisms for their recruitment, we measured chemokine mRNAs in the contused rat spinal cord, using specific and sensitive reverse transcriptase polymerase chain reaction (RT-PCR) dot-blot hybridization assays. The neutrophil chemoattractant GRO-alpha was 30-fold higher than control values at 6 hr postinjury and decayed rapidly thereafter. LIX, a highly related alpha-chemokine, also was elevated early postinjury. Monocyte chemoattractant peptide (MCP)-1 and MCP-5 mRNAs, potent chemoattractants for monocytes, were significantly elevated at the lesion epicenter at 12 and 24 hr postinjury and declined thereafter. Interferon-gamma-inducible protein, 10 kDa (IP-10), chemoattractant towards activated T-lymphocytes, was significantly elevated at 6 and 12 hr postinjury. The dendritic cell chemoattractant MIP-3alpha also was increased, perhaps contributing to the development of T-cell autoreactivity to neural components after spinal cord injury (SCI) in rats. Other beta-chemokines, including MIP-1alpha and RANTES (regulated on expression normal T-cell expressed and secreted), were minimally affected by SCI. Expression of chemokines, therefore, directly precedes the influx of target neutrophils, monocytes, and T-cells into the spinal cord postinjury, as noted previously. Thus, selective chemokine expression may be integral to inflammatory processes within the injured spinal cord as a mechanism of recruitment for circulating leukocytes.

Neurotrophin-3 and brain-derived neurotrophic factor induce oligodendrocyte proliferation and myelination of regenerating axons in the contused adult rat spinal cord.

Functional loss after spinal cord injury (SCI) is caused, in part, by demyelination of axons surviving the trauma. Neurotrophins have been shown to induce oligodendrogliagenesis in vitro, but stimulation of oligodendrocyte proliferation and myelination by these factors in vivo has not been examined. We sought to determine whether neurotrophins can induce the formation of new oligodendrocytes and myelination of regenerating axons after SCI in adult rats. In this study, fibroblasts producing neurotrophin-3 (NT-3), brain-derived neurotrophic factor (BDNF), ciliary neurotrophic factor, nerve growth factor, basic fibroblast growth factor, or beta-galactosidase (control grafts) were transplanted subacutely into the contused adult rat spinal cord. At 10 weeks after injury, all transplants contained axons. NT-3 and BDNF grafts, however, contained significantly more axons than control or other growth factor-producing grafts. In addition, significantly more myelin basic protein-positive profiles were detected in NT-3 and BDNF transplants, suggesting enhanced myelination of ingrowing axons within these neurotrophin-producing grafts. To determine whether augmented myelinogenesis was associated with increased proliferation of oligodendrocyte lineage cells, bromodeoxyuridine (BrdU) was used to label dividing cells. NT-3 and BDNF grafts contained significantly more BrdU-positive oligodendrocytes than controls. The association of these new oligodendrocytes with ingrowing myelinated axons suggests that NT-3- and BDNF-induced myelinogenesis resulted, at least in part, from expansion of oligodendrocyte lineage cells, most likely the endogenous oligodendrocyte progenitors. These findings may have significant implications for chronic demyelinating diseases or CNS injuries.

Cytokine mRNA profiles in contused spinal cord and axotomized facial nucleus suggest a beneficial role for inflammation and gliosis.

We have studied temporal mRNA expression patterns for interleukin-1beta (IL-1beta), tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), macrophage colony stimulating factor (M-CSF), and transforming growth factor-beta1 (TGF-beta1) in two rat injury paradigms with very different cellular inflammatory reactions: contussion of the spinal cord and axotomy of the facial nerve. Our comparative analyses using semiquantitative reverse transcription polymerase chain reaction (RT-PCR) show an early and robust upregulation of IL-1beta, TNF-alpha, IL-6, and M-CSF mRNAs in spinal cord after contusion injury. Peak expression of these mRNAs was transient and returned to control levels by 24 h postinjury. In contrast, expression of IL-1beta and TNF-alpha mRNAs in the axotomized facial nucleus was minimal and delayed, and levels of M-CSF mRNA remained unaltered. Similar to injured spinal cord, the axotomized nucleus showed a dramatic and early upregulation of IL-6 mRNA, but unlike spinal cord, IL-6 mRNA levels subsided only gradually. Both injury paradigms showed gradually increasing levels of TGF-beta1 mRNA which were maximal at 7 days postinjury. RT-PCR analyses were also performed on isolated blood-borne mononuclear cells and neutrophils. The results showed that these cells contain high levels of IL-1beta and M-CSF mRNAs, moderate levels of TGF-beta and TNF-alpha mRNAs, and minimal levels of IL-6 mRNA. The RT-PCR analyses together with histological observations indicate that expression of the proinflammatory cytokines IL-1beta, TNF-alpha, and IL-6 is short-lived and self-limited after contusion injury, and that it occurs primarily within endogenous glial cells. Transient expression of these molecules likely triggers secondary events which may be beneficial to wound repair and regeneration.

Brain-derived neurotrophic factor stimulates hindlimb stepping and sprouting of cholinergic fibers after spinal cord injury.

Neurotrophic factors have been proposed as a therapeutic treatment for traumatic brain and spinal cord injury. The present study determined whether exogenous administration of one such factor, brain-derived neurotrophic factor (BDNF), could effect behavioral recovery and/or histopathological changes after spinal cord injury. Adult rats received a mild or moderate contusion injury or complete transection of the mid-thoracic spinal cord. Immediately thereafter, they were infused intrathecally with vehicle or BDNF for 28 days. Behavioral recovery was evaluated for 6 weeks after injury, at which time the rats were sacrificed and the spinal cord tissue was examined histologically. The infusion of BDNF resulted in acute stimulation of hindlimb activity. These effects included activation of alternating airstepping in injured rats when the hindlimbs were unloaded as well as slight improvements in the rate of recovery in open field locomotion score. BDNF infusion was also associated with enhanced growth of cholinergic fibers at the injury epicenter, but did not affect white matter sparing or density of serotonergic axons at or below the injury site. Based on immunohistochemical detection of BDNF protein distribution, these described effects are likely to be mediated by the activation of cells and axons within the central injury region and the along the peripheral rim of the spinal cord. Together, these findings demonstrate that the exogenous infusion of BDNF after spinal trauma can influence postinjury outcome through mechanisms that include acute stimulation of hindlimb activity and neuritogenesis at the injury site.

Phosphorus-31 magnetic resonance spectroscopy studies of pig spinal cord injury. Myelin changes, intracellular pH, and bioenergetics.

RATIONALE AND OBJECTIVES: Phosphorus-31 (31P) nuclear magnetic resonance (NMR) spectroscopy was used to monitor changes in phosphocreatine (PCr), adenosine triphosphate (ATP), inorganic phosphate (Pi), intracellular pH (pHi), and free magnesium in the in vivo pig spinal cord after injury. METHODS: Phosphorus-31 NMR spectra were acquired from healthy (n = 4) and injured pig spinal cords (n = 8) under in vivo conditions using a 4.7-tesla spectrometer. Spinal cords were injured by dropping a 20-g weight from 20 cm onto the surgically exposed cord surface. RESULTS: In vivo spectra of injured cords revealed a reduction in ATP, PCr, pHi, and an increase in Pi. In addition, a broad resonance that is likely to arise from myelin phospholipids was reduced significantly after injury. CONCLUSIONS: Phosphorus-31 NMR can be used to follow in vivo changes in high energy phosphates after injury and may have the potential to follow changes in myelin structure. This technique may prove important in the study of myelin breakdown after secondary, nonreversible spinal cord injury. Changes in high energy phosphates and pHi did not seem to parallel these putative changes in myelin structure.