The multimolecular cascade of spinal cord injury. Studies on prostanoids, calcium, and proteinases

Induction of Neural Differentiation and Protection by a Novel Slow-Release Nanoparticle Estrogen Construct in a Rat Model of Spinal Cord Injury

Spinal cord injury (SCI) is a complex debilitating condition leading to permanent life-long neurological deficits. Estrogen (E2) treatment is known to be neuroprotectant in SCI. This hormone is highly pleiotropic and has been shown to decrease apoptosis, modulate calcium signaling, regulate growth factor expression, act as an anti-inflammatory, and drive angiogenesis. These beneficial effects were found in our earlier study at the low dose of 10 µg/kg E2 in rats. However, the dose remains non-physiologic, which poses a safety hurdle for clinical use. Thus, we recently devised/constructed a fast release nanoparticle (NP) estrogen embedded (FNP-E2) construct and tested a focal delivery system in a contused SCI rat model which showed protection in the short run. In the current study, we have developed a novel slow-release NP estrogen (SNP-E2) delivery system that shows sustained release of E2 in the injured spinal cord and no systemic exposure in the host. The study of E2 release and kinetics of this SNP-E2 construct in vitro and in vivo supported this claim. Delivery of E2 to the injured spinal cord via this approach reduced inflammation and gliosis, and induced microglial differentiation of M1 to M2 in rats after SCI. Analysis of spinal cord samples showed improved myelination and survival signals (AKT) as demonstrated by western blot analysis. SNP-E2 treatment also induced astrocytic differentiation into neuron-like (MAP2/NeuN) cells, supported the survival of oligodendrocyte precursor cells (OPC), and improved bladder and locomotor function in rats following SCI. These data suggest that this novel delivery strategy of SNP-E2 to the injured spinal cord may provide a safe and effective therapeutic approach to treat individuals suffering from SCI.

TiO2-Nanowired Delivery of Chinese Extract of Ginkgo biloba EGb-761 and Bilobalide BN-52021 Enhanced Neuroprotective Effects of Cerebrolysin Following Spinal Cord Injury at Cold Environment

Military personnel during combat or peacekeeping operations are exposed to extreme climates of hot or cold environments for longer durations. Spinal cord injury is quite common in military personnel following central nervous system (CNS) trauma indicating a possibility of altered pathophysiological responses at different ambient temperatures. Our previous studies show that the pathophysiology of brain injury is exacerbated in animals acclimated to cold (5 °C) or hot (30 °C) environments. In these diverse ambient temperature zones, trauma exacerbated oxidative stress generation inducing greater blood-brain barrier (BBB) permeability and cell damage. Extracts of Ginkgo biloba EGb-761 and BN-52021 treatment reduces brain pathology following heat stress. This effect is further improved following TiO₂ nanowired delivery in heat stress in animal models. Several studies indicate the role of EGb-761 in attenuating spinal cord induced neuronal damages and improved functional deficit. This is quite likely that these effects are further improved following nanowired delivery of EGb-761 and BN-52021 with cerebrolysin-a balanced composition of several neurotrophic factors and peptide fragments in spinal cord trauma. In this review, TiO₂ nanowired delivery of EGb-761 and BN-52021 with nanowired cerebrolysin is examined in a rat model of spinal cord injury at cold environment. Our results show that spinal cord injury aggravates cord pathology in cold-acclimated rats and nanowired delivery of EGb-761 and BN-52021 with cerebrolysin significantly induced superior neuroprotection, not reported earlier.

Inhibiting store-operated calcium entry attenuates white matter secondary degeneration following SCI

Axonal degeneration plays a key role in the pathogenesis of numerous neurological disorders including spinal cord injury. After the irreversible destruction of the white matter elements during the primary (mechanical) injury, spared axons and their supporting glial cells begin to breakdown causing an expansion of the lesion site. Here we mechanistically link external sources of calcium entry through axoplasmic reticulum calcium store depletion that contributes to secondary axonal degeneration through a process called store-operated calcium entry. There is increasing evidence suggesting that store-operated calcium entry impairment is responsible for numerous disorders. Nevertheless, its role following spinal cord injury remains poorly understood. We hypothesize that store-operated calcium entry mediates secondary white matter degeneration after spinal cord injury. We used our previously published model of laser-induced spinal cord injury to focally transect mid cervical dorsal column axons from live 6-8-week-old heterozygous CNPase^GFP/+: Thy1^YFP+ double transgenic murine spinal cord preparations (five treated, eight controls) and documented the dynamic changes in axons over time using two-photon excitation microscopy. We report that 1 hour delayed treatment with YM-58483, a potent inhibitor of store-operated calcium entry, significantly decreased intra-axonal calcium accumulation, axonal dieback both proximal and distal to the lesion site, reduced secondary axonal "bystander" damage acutely after injury, and promoted greater oligodendrocyte survival compared to controls. We also targeted store-operated calcium entry following a clinically relevant contusion spinal cord injury model in vivo. Adult, 6-8-week-old Advillin-Cre: Ai9 mice were subjected to a mild 30 kdyn contusion and imaged to observe secondary axonal degeneration in live animals. We found that delayed treatment with YM-58483 increased axonal survival and reduced axonal spheroid formation compared to controls (n = 5 mice per group). These findings suggest that blocking store-operated calcium entry acutely is neuroprotective and introduces a novel target to prevent pathological calcium entry following spinal cord injury using a clinically relevant model.

Differential expression of ryanodine receptor isoforms after spinal cord injury

Ryanodine receptors (RyRs) are highly conductive intracellular Ca²⁺ release channels and are widely expressed in many tissues, including the central nervous system. RyRs have been implicated in intracellular Ca²⁺ overload which can drive secondary damage following traumatic injury to the spinal cord (SCI), but the spatiotemporal expression of the three isoforms of RyRs (RyR1-3) after SCI remains unknown. Here, we analyzed the gene and protein expression of RyR isoforms in the murine lumbar dorsal root ganglion (DRG) and the spinal cord lesion site at 1, 2 and 7 d after a mild contusion SCI. Quantitative RT PCR analysis revealed that RyR3 was significantly increased in lumbar DRGs and at the lesion site at 1 and 2 d post contusion compared to sham (laminectomy only) controls. Additionally, RyR2 expression was increased at 1 d post injury within the lesion site. RyR2 and -3 protein expression was localized to lumbar DRG neurons and their spinal projections within the lesion site acutely after SCI. In contrast, RyR1 expression within the DRG and lesion site remained unaltered following trauma. Our study shows that SCI initiates acute differential expression of RyR isoforms in DRG and spinal cord.

Targeting Enolase in Reducing Secondary Damage in Acute Spinal Cord Injury in Rats

Spinal cord injury (SCI) is a complex debilitating condition leading to permanent life-long neurological deficits. The complexity of SCI suggests that a concerted multi-targeted therapeutic approach is warranted to optimally improve function. Damage to spinal cord is complicated by an increased detrimental response from secondary injury factors mediated by activated glial cells and infiltrating macrophages. While elevation of enolase especially neuron specific enolase (NSE) in glial and neuronal cells is believed to trigger inflammatory cascades in acute SCI, alteration of NSE and its subsequent effects in acute SCI remains unknown. This study measured NSE expression levels and key inflammatory mediators after acute SCI and investigated the role of ENOblock, a novel small molecule inhibitor of enolase, in a male Sprague-Dawley (SD) rat SCI model. Serum NSE levels as well as cytokines/chemokines and metabolic factors were evaluated in injured animals following treatment with vehicle alone or ENOblock using Discovery assay. Spinal cord samples were also analyzed for NSE and MMPs 2 and 9 as well as glial markers by Western blotting. The results indicated a significant decrease in serum inflammatory cytokines/chemokines and NSE, alterations of metabolic factors and expression of MMPs in spinal cord tissues after treatment with ENOblock (100 µg/kg, twice). These results support the hypothesis that activation of glial cells and inflammation status can be modulated by regulation of NSE expression and activity. Analysis of SCI tissue samples by immunohistochemistry confirmed that ENOblock decreased gliosis which may have occurred through reduction of elevated NSE in rats. Overall, elevation of NSE is deleterious as it promotes extracellular degradation and production of inflammatory cytokines/chemokines and metabolic factors which activates glia and damages neurons. Thus, reduction of NSE by ENOblock may have potential therapeutic implications in acute SCI.

Axonal pathology in traumatic brain injury

Over the past 70years, diffuse axonal injury (DAI) has emerged as one of the most common and important pathological features of traumatic brain injury (TBI). Axons in the white matter appear to be especially vulnerable to injury due to the mechanical loading of the brain during TBI. As such, DAI has been found in all severities of TBI and may represent a key pathologic substrate of mild TBI (concussion). Pathologically, DAI encompasses a spectrum of abnormalities from primary mechanical breaking of the axonal cytoskeleton, to transport interruption, swelling and proteolysis, through secondary physiological changes. Depending on the severity and extent of injury, these changes can manifest acutely as immediate loss of consciousness or confusion and persist as coma and/or cognitive dysfunction. In addition, recent evidence suggests that TBI may induce long-term neurodegenerative processes, such as insidiously progressive axonal pathology. Indeed, axonal degeneration has been found to continue even years after injury in humans, and appears to play a role in the development of Alzheimer's disease-like pathological changes. Here we review the current understanding of DAI as a uniquely mechanical injury, its histopathological identification, and its acute and chronic pathogenesis following TBI.

High expression of STIM1 in the early stages of diffuse axonal injury

Increased intracellular calcium ([Ca(2+)](i)) is a key pathological mechanism involved in secondary neuronal injury and cell death due to diffuse axonal injury (DAI). To date, this increased [Ca(2+)](i) is believed to be mainly caused by dysfunction of voltage-gated sodium channels and mechanoporation of the plasma membrane. Store-operated calcium entry (SOCE) is another source of Ca(2+) influx, and stromal interaction molecule 1 (STIM1) is considered as a sensor and a regulator of SOCE. In this study, we established a DAI in vivo model in rats by lateral head rotation. Using immunohistochemistry, real-time RT-PCR and Western blot, we investigated STIM1 expression levels in the cerebral cortex of rats after lateral head rotational injury. Results revealed notably high STIM1 expression in neurons in the early stages (within 24 h) of DAI. STIM1 began to increase at 6 h post-injury (PI) peaked at 12 h PI, and then gradually decreased. At 2 days PI, STIM1 expression in the injury group showed no significant difference compared with that of the control group. These results indicate that abnormal SOCE may participate in Ca(2+) overload of neurons in the early stages after DAI via enhanced STIM1 expression.

Messenger RNA oxidation occurs early in disease pathogenesis and promotes motor neuron degeneration in ALS

Background

Accumulating evidence indicates that RNA oxidation is involved in a wide variety of neurological diseases and may be associated with neuronal deterioration during the process of neurodegeneration. However, previous studies were done in postmortem tissues or cultured neurons. Here, we used transgenic mice to demonstrate the role of RNA oxidation in the process of neurodegeneration.

Methodology/Principal Findings

We demonstrated that messenger RNA (mRNA) oxidation is a common feature in amyotrophic lateral sclerosis (ALS) patients as well as in many different transgenic mice expressing familial ALS-linked mutant copper-zinc superoxide dismutase (SOD1). In mutant SOD1 mice, increased mRNA oxidation primarily occurs in the motor neurons and oligodendrocytes of the spinal cord at an early, pre-symptomatic stage. Identification of oxidized mRNA species revealed that some species are more vulnerable to oxidative damage, and importantly, many oxidized mRNA species have been implicated in the pathogenesis of ALS. Oxidative modification of mRNA causes reduced protein expression. Reduced mRNA oxidation by vitamin E restores protein expression and partially protects motor neurons.

Conclusion/Significance

These findings suggest that mRNA oxidation is an early event associated with motor neuron deterioration in ALS, and may be also a common early event preceding neuron degeneration in other neurological diseases.

Calpain inhibitors and antioxidants act synergistically to prevent cell necrosis: effects of the novel dual inhibitors (cysteine protease inhibitor and antioxidant) BN 82204 and its pro-drug BN 82270

Cell death is a common feature observed in neurodegenerative disorders, and is often associated with calpain activation and overproduction of reactive oxygen species (ROS). This study investigated the use of calpain inhibitors and antioxidants in combination to protect cells against necrosis. Maitotoxin (MTX), which induces a massive influx of calcium, was used to provoke neuronal cell death. This toxin increased, in a concentration-dependent manner, both calpain activity and ROS formation. Calpain inhibitors or antioxidants inhibited MTX-induced necrosis only marginally (below 20%), whereas their association protected against cell death by 40-66% in a synergistic manner. BN 82204, which possesses both calpain-cathepsin L inhibitory and antioxidant properties, and its acetylated pro-drug BN 82270, totally protected cells at 100 microm. The pro-drug BN 82270, which had better cell penetration, was twice as effective as the active principle BN 82204 in protecting glioma C6 or neuroblastoma SHSY5Y cells against death. These results suggest the potential therapeutic relevance of using a single molecule with multiple activities (cysteine protease inhibitor/antioxidant), and warrant further in vivo investigations in models of neuronal disorders.

Secondary medulla oblongata involvement following middle cervical spinal cord injury associated with latent traumatic instability in a patient with ossification of the posterior longitudinal ligament

STUDY DESIGN

A case report.

OBJECTIVES

To report a rare case of extension of edema and hemorrhage from initial C4-5 spinal injury to the medulla oblongata.

SETTING

Center for Spinal Disorders and Injuries, Bibai Rosai Hospital, Japan.

METHODS

A 68-year-old man with ossification of the posterior longitudinal ligament (OPLL) had sustained tetraplegia after tumbling over a stone. Initially, the patient was diagnosed with an acute C4-5 spinal cord injury without radiological abnormalities and was treated conservatively. At 7 h after the injury, the patient had an ascending neurological deficit, which required respiratory assistance. Magnetic resonance imaging revealed a marked swelling of the spinal cord above C4-5 extending to the medulla oblongata.

RESULTS

Retrospective radiological assessment revealed that the spine was unstable at the injury level because of discontinuities in both anterior and posterior longitudinal ligaments. There was also signal intensity change within the retropharyngeal space at the C4-5 intervertebral disc. This injured segment was highly vulnerable to post-injury dynamic stenosis and easily sustained secondary neural damage.

CONCLUSIONS

This case report emphasizes a careful radiological assessment of latent structural instability in patients with OPLL in order to detect and prevent deteriorative change in the spinal cord.

Traumatic axonal injury induces proteolytic cleavage of the voltage-gated sodium channels modulated by tetrodotoxin and protease inhibitors

We demonstrated previously that dynamic stretch injury of cultured axons induces structural changes and Ca2+ influx modulated by tetrodotoxin (TTX)-sensitive voltage-gated sodium channels (NaChs). In the present study, we evaluated potential damage to the NaCh alpha-subunit, which can cause noninactivation of NaChs. In addition, we explored the effects of pre-injury and post-injury treatment with TTX and protease inhibition on proteolysis of the NaCh alpha-subunit and intra-axonal calcium levels ([Ca2+]i) over 60 min after trauma. After stretch injury, we found that [Ca2+]i continued to increase in untreated axons for at least 60 min. We also observed that the III-IV intra-axonal loop of the NaCh alpha-subunit was proteolyzed between 5 and 20 min after trauma. Pre-injury treatment of the axons with TTX completely abolished the posttraumatic increase in [Ca2+]i and proteolysis of the NaCh alpha-subunit. In addition, both pre-injury and post-injury inhibition of protease activity attenuated long-term increases in [Ca2+]i as well as mitigating degradation of the NaCh alpha-subunit. These results suggest a unique "feed-forward" deleterious process initiated by mechanical trauma of axons. Na+ influx through NaChs resulting from axonal deformation triggers initial increases in [Ca2+]i and subsequent proteolysis of the NaCh-subunit. In turn, degradation of the alpha-subunit promotes persistent elevations in [Ca2+]i, fueling additional pathologic changes. These observations may have important implications for developing therapeutic strategies for axonal trauma.

Calpain inhibitor prevented apoptosis and maintained transcription of proteolipid protein and myelin basic protein genes in rat spinal cord injury

Spinal cord injury (SCI) is associated with progressive neurodegeneration and dysfunction. Multiple cellular and molecular mechanisms are involved in this pathogenesis. In particular, the activation of proteases following trauma can cause apoptosis in the spinal cord. Calpain, a calcium-dependent cysteine protease, plays a major role in apoptosis following trauma. We identified apoptosis and decrease in transcription of the genes for proteolipid protein (PLP) and myelin basic protein (MBP) in five 1-cm long spinal cord segments (S1, distant rostral; S2, near rostral; S3, lesion; S4, near caudal; and S5, distant caudal) 24 h after induction of SCI (40 g.cm force) in rats by weight-drop method. Sham rats underwent laminectomy and did not receive injury. Internucleosomal DNA fragmentation occurred prominently in the lesion (S3), moderately in near segments (S2 and S4), and slightly in distant segments (S1 and S5) of injured rats, indicating the occurrence of apoptosis in the lesion and penumbra. Levels of transcription of PLP and MBP were reduced highly in the lesion and moderately in near segments, suggesting that apoptotic loss of cells impaired biosynthesis of two important structural components of myelin. Immediate administration of the calpain inhibitor E-64-d (1 mg/kg) to injured rats prevented apoptosis and restored transcription of these genes, indicating the therapeutic efficacy of calpain inhibitor for treatment of SCI.

Secondary injury mechanisms of spinal cord trauma: a novel therapeutic approach for the management of secondary pathophysiology with the sodium channel blocker riluzole

Traumatic spinal cord injury is a consequence of a primary mechanical insult and a sequence of progressive secondary pathophysiological events that confound efforts to mitigate neurological deficits. Pharmacotherapy aimed at reducing the secondary injury is limited by a narrow therapeutic window. Thus, novel drug strategies must target early pathological mechanisms in order to realize the promise of efficacy for this form of neurotrauma. Research has shown that an accumulation of intracellular sodium as a result of trauma-induced perturbation of voltage-sensitive sodium channel activity is a key early mechanism in the secondary injury cascade. As such, voltage-sensitive sodium channels are an important therapeutic target for the treatment of spinal cord trauma. This review describes the evolution of acute spinal cord injury and provides a rationale for the clinical utility of sodium channel blockers, particularly riluzole, in the management of spinal cord trauma.

Histologic characterization of acute spinal cord injury treated with intravenous methylprednisolone

OBJECTIVE

Many substances have been investigated for attenuation of spinal cord injury after acute trauma; however, pharmacologically only steroid administration has shown clinical benefits. This study attempts to characterize local spinal cord histologic response to human dose equivalent (HDE) intravenous methylprednisolone (MP) administration in a rodent model of acute spinal cord injury.

DESIGN

Forty-eight Sprague-Dawley rats were divided equally into control and experimental groups. Each group was subdivided into eight sets of three animals each, according to postinjury intervals. Paraplegia after lower thoracic laminectomy was achieved using a standardized weight drop technique.

INTERVENTION

Within one hour, experimental animals were treated with HDE MP followed by 23-hour continuous infusion of HDE MP. Spinal cords were harvested at variable intervals postinjury and prepared for histologic/immunohistochemistry examination.

MAIN OUTCOME MEASUREMENTS

Edema, necrosis, and glial fibrillary acidic protein (GFAP) positivity in the specimens from treated/control groups were graded by microscopy and immunohistochemistry staining and compared in a blinded manner by a qualified neuropathologist and senior authors.

RESULTS

Minimal differences were observed between control and MP-treated animals at zero and four hours. At eight hours, increased white matter and medullary edema was evident in control versus MP-treated rats. This trend continued through twelve, sixteen, twenty-four, forty-eight, and seventy-two hours. No difference was observed in the astrocytic response to injury by GFAP immunohistochemistry between the groups.

CONCLUSIONS

Histologically, MP reduces the development of severe edema and preserves spinal cord architecture adjacent to the site of injury. In contrast, MP does not alter the development of spinal cord necrosis or astrocytic response at the zone of injury.

Traumatic axonal injury induces calcium influx modulated by tetrodotoxin-sensitive sodium channels

Diffuse axonal injury (DAI) is one of the most common and important pathologies resulting from the mechanical deformation of the brain during trauma. It has been hypothesized that calcium influx into axons plays a major role in the pathophysiology of DAI. However, there is little direct evidence to support this hypothesis, and mechanisms of potential calcium entry have not been explored. In the present study, we used an in vitro model of axonal stretch injury to evaluate the extent and modulation of calcium entry after trauma. Using a calcium-sensitive dye, we observed a dramatic increase in intra-axonal calcium levels immediately after injury. Axonal injury in a calcium-free extracellular solution resulted in no change in calcium concentration, suggesting an extracellular source for the increased post-traumatic calcium levels. We also found that the post-traumatic change in intra-axonal calcium was completely abolished by the application of the sodium channel blocker tetrodotoxin or by replacement of sodium with N-methyl-d-glucamine. In addition, application of the voltage-gated calcium channel (VGCC) blocker omega-conotoxin MVIIC attenuated the post-traumatic increase in calcium. Furthermore, blockade of the Na(+)-Ca(2+) exchanger with bepridil modestly reduced the calcium influx after injury. In contrast to previously proposed mechanisms of calcium entry after axonal trauma, we found no evidence of calcium entry through mechanically produced pores (mechanoporation). Rather, our results suggest that traumatic deformation of axons induces abnormal sodium influx through mechanically sensitive Na(+) channels, which subsequently triggers an increase in intra-axonal calcium via the opening of VGCCs and reversal of the Na(+)-Ca(2+) exchanger.

Cell death in spinal cord injury (SCI) requires de novo protein synthesis. Calpain inhibitor E-64-d provides neuroprotection in SCI lesion and penumbra

Degradation of cytoskeletal proteins by calpain, a Ca(2+)-dependent cysteine protease, may promote neuronal apoptosis in the lesion and surrounding areas following spinal cord injury (SCI). Clinically relevant moderate (40 g-cm force) SCI in rats was induced at T12 by a standardized weight-drop method. Internucleosomal DNA fragmentation or apoptosis in the lesion was inhibited by 24-h treatment of SCI rats with cycloheximide (1 mg/kg), indicating a requirement for de novo protein synthesis in this process. To prove an involvement of calpain activity in mediation of apoptosis in SCI, we treated SCI rats with a cell-permeable calpain inhibitor E-64-d (1 mg/kg). Following 24-h treatment, a 5-cm-long spinal cord section centered at the lesion was collected, and divided equally into five segments (1 cm each) to determine calpain activity, as shown by degradation of the 68-kD neurofilament protein (NFP), and apoptosis as indicated by internucleosomal DNA fragmentation. Neurodegeneration propagated from the site of injury to neighboring rostral and caudal regions. Both calpain activity and apoptosis were readily detectable in the lesion, and moderately so in neighboring areas of untreated SCI rats, whereas these were almost undetectable in E-64-d-treated SCI rats, and absent in sham animals. Results indicate that apoptosis in the SCI lesion and penumbra is prominently associated with calpain activity and is inhibited by the calpain inhibitor E-64-d providing neuroprotective benefit.

Evaluation of the neuroprotective effects of sodium channel blockers after spinal cord injury: improved behavioral and neuroanatomical recovery with riluzole

OBJECT

Persistent activation of voltage-sensitive Na+ channels is associated with cellular toxicity and may contribute to the degeneration of neural tissue following traumatic brain and spinal cord injury (SCI). Pharmacological blockade of these channels can attenuate secondary pathophysiology and reduce functional deficits acutely.

METHODS

To determine the therapeutic effects of Na+ channel blockers on long-term tissue sparing and functional neurological recovery after traumatic SCI, the authors injected Wistar rats intraperitoneally with riluzole (5 mg/kg), phenytoin (30 mg/kg), CNS5546A, a novel Na+ channel blocker (15 mg/kg), or vehicle (2-HP3CD; 5 mg/kg) 15 minutes after induction of compressive SCI at C7-T1. Functional neurological recovery of coordinated hindlimb function and strength, assessed 1 week postinjury and weekly thereafter for 6 weeks, was significantly enhanced in animals treated with riluzole compared with the other treatment groups. Seven weeks postinjury the preservation of residual tissue and integrity of descending axons were determined with digital morphometrical and fluorescent histochemical analysis. All three Na+ channel blockers significantly enhanced residual tissue area at the injury epicenter compared with control. Riluzole significantly reduced tissue loss in rostrocaudal regions surrounding the epicenter, with overall sparing of gray matter and selective sparing of white matter. Also, counts of red nuclei neurons retrogradely labeled with fluorogold introduced caudal to the injury site were significantly increased in the riluzole group.

CONCLUSIONS

Systemic Na+ channel blockers, in particular riluzole, can confer significant neuroprotection after in vivo SCI and result in behavioral recovery and sparing of both gray and white matter.

E-64-d prevents both calpain upregulation and apoptosis in the lesion and penumbra following spinal cord injury in rats

Calpain, a Ca(2+)-dependent cysteine protease, has been implicated in cytoskeletal protein degradation and neurodegeneration in the lesion and adjacent areas following spinal cord injury (SCI). To attenuate apoptosis or programmed cell death (PCD) in SCI, we treated injured rats with E-64-d, a cell permeable and selective inhibitor of calpain. SCI was induced on T12 by the weight-drop (40 g-cm force) method. Within 15 min, E-64-d (1 mg/kg) in 1.5% DMSO was administered i.v. to the SCI rats. Following 24 h treatment, a 5-cm long spinal cord section with the lesion in the center was collected. The spinal cord section was divided equally into five 1-cm segments (S1: distant rostral, S2: near rostral, S3: lesion or injury, S4: near caudal and S5: distant caudal) for analysis. Determination of mRNA levels by reverse transcriptase-polymerase chain reaction (RT-PCR) indicated that ratios of bax/bcl-2 and calpain/calpastatin were increased in spinal cord segments from injured rats compared to controls. Degradation of the 68-kD neurofilament protein and internucleosomal DNA fragmentation were also increased. All of these changes were maximally increased in the lesion and gradually decreased in the adjacent areas of SCI rats, while largely undetectable in E-64-d treated rats and absent in sham controls. The results indicate that apoptosis in rat SCI appears to be associated with calpain activity which can be attenuated by the calpain inhibitor E-64-d.

Delayed apnea in patients with mid- to lower cervical spinal cord injury

STUDY DESIGN

A retrospective study of 36 patients with mid- to lower cervical spinal cord injury (CSCI) divided into two groups based on whether delayed apnea developed.

OBJECTIVES

To determine nonpulmonary risk factors associated with the development of delayed apnea in mid- to lower cervical spinal cord injury.

SUMMARY OF BACKGROUND DATA

Patients with mid- to lower cervical spinal cord injury are generally at lower risk of developing respiratory failure than those with high cervical spinal cord injury. Respiratory failure manifesting as sudden apnea may occur days or even weeks after injury without any pulmonary complications in such patients.

METHODS

An index group of eight patients with complete mid- to lower cervical spinal cord injury in whom delayed catastrophic apnea occurred were reviewed. Another group of 28 patients with cervical spinal cord injury of identical magnitude and presentation but without respiratory failure served as the control group. Six parameters presumed to be related to the delayed apnea were analyzed.

RESULTS

The extent of cord lesions was significantly different, being diffuse in most of the index patients, but focal in the majority of the control patients (P<0.001). Involvement of the C4 segment of cord appeared to be more frequent in the index group; however, the difference was not statistically significant (P = 0.091). The incidence of transient bradycardia (P<0.01) and dyspnea (P<0.001) in the index group was significantly higher than in the control group. Paralytic ileus was a much rarer event and found to be unrelated to the occurrence of apnea. In five of the eight index patients, the apnea occurred during sleep. Six of the eight index patients died of it.

CONCLUSIONS

Delayed but devastating apnea may develop in patients with mid- to lower cervical cervical spinal cord injury, even when they are clinically stable and free from any pulmonary complications. The presence of diffuse, extensive cord lesions, respiratory distress, or bradycardia with or without associated hypotension, however transient and self-limited, should be regarded as warning signs. Sleep was found to be a risky period of time.

Pretreatment with calpain inhibitor CEP-4143 inhibits calpain I activation and cytoskeletal degradation, improves neurological function, and enhances axonal survival after traumatic spinal cord injury

The pathophysiology of traumatic spinal cord injury (SCI) involves abnormal activation of the neutral cysteine protease calpain I (EC 3.4.22.17). In the present study we examined the effect of the calpain inhibitor CEP-4143 on cytoskeletal protection and neurological recovery after SCI in adult rats. Microinjection of 50 mM CEP-4143 into the T7 vertebral segment 10 min before a 35-g clip compression injury resulted in inhibition of calpain activation at 2 and 4 h postinjury, as determined by western blotting for calpain I-mediated spectrin degradation, and significantly attenuated the degradation of dephosphorylated NF200 neurofilament protein at 4 and 8 h postinjury. To examine the in vivo chronic neuroprotective effects of CEP-4143, animals underwent microinjection with saline or 50 mM CEP-4143 10 min before injury, followed by weekly blinded behavioral assessments for 6 weeks. Animals receiving CEP-4143 treatment showed significant improvement over saline-treated controls on the Basso Beattie Bresnahan locomotor rating scale (p < 0.02) and inclined plane test (p < 0.05). Counts of neurons in the red nucleus retrogradely labeled by fluoro-gold after introduction distal to the injury site were significantly higher in CEP-4143-treated animals. Finally, morphometric assessment of the injury site by computer-assisted image analysis revealed significant tissue preservation in CEP-4143-treated animals. We conclude that the calpain antagonist CEP-4143 exhibits biochemical, behavioral, and anatomical neuroprotection following traumatic SCI.

Experimental spinal cord injury: spatiotemporal characterization of elemental concentrations and water contents in axons and neuroglia

To examine the role of axonal ion deregulation in acute spinal cord injury (SCI), white matter strips from guinea pig spinal cord were incubated in vitro and were subjected to graded focal compression injury. At several postinjury times, spinal segments were removed from incubation and rapidly frozen. X-ray microanalysis was used to measure percent water and dry weight elemental concentrations (mmol/kg) of Na, P, Cl, K, Ca, and Mg in selected morphological compartments of myelinated axons and neuroglia from spinal cord cryosections. As an index of axon function, compound action potentials (CAP) were measured before compression and at several times thereafter. Axons and mitochondria in epicenter of severely compressed spinal segments exhibited early (5 min) increases in mean Na and decreases in K and Mg concentrations. These elemental changes were correlated to a significant reduction in CAP amplitude. At later postcompression times (15 and 60 min), elemental changes progressed and were accompanied by alterations in compartmental water content and increases in mean Ca. Swollen axons were evident at all postinjury times and were characterized by marked element and water deregulation. Neuroglia and myelin in severely injured epicenter also exhibited significant disruptions. In shoulder areas (adjacent to epicenter) of severely injured spinal strips, axons and mitochondria exhibited modest increases in mean Na in conjunction with decreases in K, Mg, and water content. Following moderate compression injury to spinal strips, epicenter axons exhibited early (10 min postinjury) element and water deregulation that eventually recovered to near control values (60 min postinjury). Na(+) channel blockade by tetrodotoxin (TTX, 1 microM) perfusion initiated 5 min after severe crush diminished both K loss and the accumulation of Na, Cl, and Ca in epicenter axons and neuroglia, whereas in shoulder regions TTX perfusion completely prevented subcellular elemental deregulation. TTX perfusion also reduced Na entry in swollen axons but did not affect K loss or Ca gain. Thus graded compression injury of spinal cord produced subcellular elemental deregulation in axons and neuroglia that correlated with the onset of impaired electrophysiological function and neuropathological alterations. This suggests that the mechanism of acute SCI-induced structural and functional deficits are mediated by disruption of subcellular ion distribution. The ability of TTX to reduce elemental deregulation in compression-injured axons and neuroglia implicates a significant pathophysiological role for Na(+) influx in SCI and suggests Na(+) channel blockade as a pharmacotherapeutic strategy.

Increased calpain I-mediated proteolysis, and preferential loss of dephosphorylated NF200, following traumatic spinal cord injury

We investigated the hypothesis that the Ca2+-activated protease calpain is involved in the pathophysiology of spinal cord injury, and is linked to the proteolytic degradation of cytoskeletal proteins. We report here that levels of calpain I (mu-calpain)-mediated spectrin breakdown products are increased by 15 min post-injury, with peak levels reached by 2 h post-injury. The dephosphorylated form of the neurofilament protein NF200 is substantially lost over the same time-period. A 35-g compressive injury was applied to the midthoracic rat spinal cord for 1 min, and animals were killed at 15 min, 1, 2, 4, 8, 16, and 24 h post-injury. Calpain I-mediated spectrin breakdown products accumulated post-injury, with peak levels reached at 2 h. Secondly, we have demonstrated a progressive loss of the 200,000 mol. wt neurofilament protein NF200, a cytoskeletal calpain substrate, which began within 1-2 h post-injury. Densitometric analyses confirmed that loss of NF200 is a substrate-specific phenomenon, since (i) dephosphorylated NF200 was preferentially lost while phosphorylated NF200 was relatively spared, and (ii) actin, which is not a substrate for calpain, was relatively spared following spinal cord injury. Finally, we demonstrated calpain I-mediated spectrin breakdown within NF200-positive neuronal processes post-injury. We conclude that the accumulation of spectrin breakdown products is temporally and spatially correlated with loss of dephosphorylated NF200 after spinal cord injury.

In vivo Bcl-2 oncogene neuronal expression in the rat spinal cord

STUDY DESIGN

An acute mechanical rat spinal cord injury model was used to investigate in vivo Bcl-2 oncogene overexpression in neuronal tissue.

OBJECTIVES

To introduce the Bcl-2 oncogene in vivo by a recombinant adenovirus vector into rat spinal cord tissue, and to investigate any potential protective effect on neural tissue in the zone of injury in a rat spinal cord model.

SUMMARY OF BACKGROUND DATA

The Bcl-2 oncogene inhibits apoptotic and necrotic neural cell death in vitro by regulating an antioxidant pathway at sites of free radical generation. Thus, overexpression of the Bcl-2 oncogene may have a role in limiting the secondary injury cascade of spinal cord injury through its regulation of antioxidants.

METHODS

After confirmation of Bcl-2 gene expression in vitro and in vivo in the rat spinal cord, a weight-drop spinal cord injury model was performed on seven rats with prior Bcl-2 inoculation, and on seven rats with prior B-gal inoculation (controls).

RESULTS

In vivo Bcl-2 expression was documented by immunostaining. After spinal cord harvest, quantification of percentage preserved tissue at the spinal cord injury site suggested that Bcl-2 overexpression confers neuroprotection.

CONCLUSIONS

In vivo Bcl-2 oncogene overexpression was successfully induced in neuronal tissue. After Bcl-2 oncogene expression in the rat spinal cord, the zone of microscopic injury was diminished. Further investigation of the Bcl-2 oncogene for potentially enhancing neuronal survival after spinal cord injury appears indicated.

Calcium-mediated intracellular messengers modulate the serotonergic effects on axonal excitability

We carried out experiments to investigate the mechanisms of serotonin-induced axonal excitability changes using isolated dorsal columns from young (seven to 11-day-old) Long-Evan's hooded rats. Conducting action potentials were activated by submaximal (50%) and supramaximal constant current electrical stimuli and recorded with glass micropipette electrodes. In experiment 1, to study Ca(2+)-mediated mechanisms, we superfused the preparations with Ringer solutions containing varying Ca2+ concentrations. Following superfusion with Ca(2+)-free Ringer solution for 4 h, we tested initial responses to serotonin agonists. Studies then were repeated after preparations had been washed for 1 h with Ringer solution containing 1.5 mM Ca2+ and 1.5 mM Mg2+. After 4 h superfusion of Ca(2+)-free Ringer solution, quipazine (a serotonin2A agonist, 100 microM) did not induce significant axonal excitability changes (amplitude change of 1.4 +/- 1.3%, percentage of predrug control level, +/-S.D., n = 6). A 100 microM concentration of 8-hydroxy-dipropylaminotetralin (a serotonin1A agonist) reduced response amplitudes by 36.3 +/- 4.2% (+/-S.D., P < 0.0005, n = 7) and prolonged latencies by 22.3 +/- 4.3% (+/-S.D., P < 0.0005, n = 7). Application of serotonin (100 microM) decreased amplitudes by 6.6 +/- 5.0% (+/-S.D., P < 0.05, n = 6). Extracellular calcium concentration ([Ca2+]e) was measured at various depths in the dorsal column with ion-selective microelectrodes. Four hours' superfusion with Ca(2+)-free Ringer solution reduced [Ca2+]e to less than 0.1 mM in dorsal columns. In 1.5 mM Ca2+ Ringer solution, quipazine increased the amplitudes by 38.3 +/- 5.8% (P < 0.0005, n = 6). Likewise, serotonin increased the amplitudes by 13.8 +/- 4.9% (P < 0.005, n = 6). In contrast however, 8-hydroxy-dipropylaminotetralin still reduced amplitudes by 35.0 +/- 6.4% (P < 0.0005, n = 7) and prolonged latencies by 24.1 +/- 4.5% (P < 0.0005, n = 7). In experiment 2, we investigated calcium-dependent and cAMP-mediated protein kinase signalling pathways to evaluate their role as intracellular messengers for serotonin2A receptor activation. Two protein kinase inhibitors, 50 microM H7 (an inhibitor of protein kinase C and c-AMP dependent protein kinase) and 100 microM D-sphingosine (an inhibitor of protein kinase A and C) effectively eliminated the excitatory effects of the serotonin2A agonist. 100 microM cadmium (a Ca2+ channel blocker) also blocked the effects of quipazine. Neither these protein kinase inhibitors nor cadmium alone affected action potential amplitudes. These results suggest that replacing Ca2+ with Mg2+ blocks the excitatory effects of quipazine but does not prevent the inhibitory effects of 8-hydroxy-dipropylaminotetralin, and calcium-mediated protein kinase mechanisms modulate axonal excitability changes induced by serotonin and its agonist.

Local blockade of sodium channels by tetrodotoxin ameliorates tissue loss and long-term functional deficits resulting from experimental spinal cord injury

Although relatively little is known of the mechanisms involved in secondary axonal loss after spinal cord injury (SCI), recent data from in vitro models of white matter (WM) injury have implicated abnormal sodium influx as a key event. We hypothesized that blockade of sodium channels after SCI would reduce WM loss and long-term functional deficits. To test this hypothesis, a sufficient and safe dose (0.15 nmol) of the potent Na+ channel blocker tetrodotoxin (TTX) was determined through a dose-response study. We microinjected TTX or vehicle (VEH) into the injury site at 15 min after a standardized contusive SCI in the rat. Behavioral tests were performed 1 d after injury and weekly thereafter. Quantitative histopathology at 8 weeks postinjury showed that TTX treatment significantly reduced tissue loss at the injury site, with greater effect on sparing of WM than gray matter. TTX did not change the pattern of chronic histopathology typical of this SCI model, but restricted its extent, tripled the area of residual WM at the epicenter, and reduced the average length of the lesions. Serotonin immunoreactivity caudal to the epicenter, a marker for descending motor control axons, was nearly threefold that of VEH controls. The increase in WM at the epicenter was significantly correlated with the decrease in functional deficits. The TTX group exhibited a significantly enhanced recovery of coordinated hindlimb functions, more normal hindlimb reflexes, and earlier establishment of a reflex bladder. The results demonstrate that Na+ channels play a critical role in WM loss in vivo after SCI.

Mechanism of calcium entry during axon injury and degeneration

Axon degeneration is a hallmark consequence of chemical neurotoxicant exposure (e.g., acrylamide), mechanical trauma (e.g., nerve transection, spinal cord contusion), deficient perfusion (e.g., ischemia, hypoxia), and inherited neuropathies (e.g., infantile neuroaxonal dystrophy). Regardless of the initiating event, degeneration in the PNS and CNS progresses according to a characteristic sequence of morphological changes. These shared neuropathologic features suggest that subsequent degeneration, although induced by different injury modalities, might evolve via a common mechanism. Studies conducted over the past two decades indicate that Ca2+ accumulation in injured axons has significant neuropathic implications and is a potentially unifying mechanistic event. However, the route of Ca2+ entry and the involvement of other relevant ions (Na+, K+) have not been adequately defined. In this overview, we discuss evidence for reverse operation of the Na+-Ca2+ exchanger as a primary route of Ca2+ entry during axon injury. We propose that diverse injury processes (e.g., axotomy, ischemia, trauma) which culminate in axon degeneration cause an increase in intraaxonal Na+ in conjunction with a loss of K+ and axolemmal depolarization. These conditions favor reverse Na+-Ca2+ exchange operation which promotes damaging extraaxonal Ca2+ entry and subsequent Ca2+-mediated axon degeneration. Deciphering the route of axonal Ca2+ entry is a fundamental step in understanding the pathophysiologic processes induced by chemical neurotoxicants and other types of nerve damage. Moreover, the molecular mechanism of Ca2+ entry can be used as a target for the development of efficacious pharmacotherapies that might be useful in preventing or limiting irreversible axon injury.

Comparative study of prostaglandin E2 production in chick spinal cord and meninges

In chick spinal cord the presence of low affinity (KD = 2.2 microM) receptors for prostaglandin E2 (PGE2) raises the question whether spinal cord possesses a PGE2 biosynthetic capacity able to activate these receptors. The production of PGE2 in spinal cord and meninges was investigated by enzyme immunoassay. Spinal cord exhibited a 30- to 100-fold lower PGE2 biosynthetic capacity compared to meninges, but can generate PGE2 resulting in micromolar concentrations, sufficient to activate the low affinity PGE2 receptors. It is suggested that in physiological conditions, PGE2 synthesized within the spinal cord might locally activate the low affinity PGE2 receptors, whereas in pathological situations, after disruption of the blood-spinal cord barrier, PGE2 produced by the meninges might be accessible to spinal cord PGE2 receptors, and thus largely contribute to their saturation.

Purification of active calpain by affinity chromatography on an immobilized peptide inhibitor

Most purification schemes of calpain (CANP) involve a number of chromatographic steps. The final preparations often contain impurities, including degradation fragments. Two peptide-affinity columns were developed, using peptides of 27 amino acids and 30 amino acids, corresponding to the products of exons 1B and 1C, respectively, of the natural inhibitor (calpastatin) gene, coupled to CNBr-activated Sepharose 4B. Crude preparations of calpain, isolated by anion-exchange chromatography on a DEAE-Sepharose column, were incubated with a reversible or an irreversible synthetic inhibitor which blocks the catalytic subunit of the enzyme in the inactive 80-kDa form. The crude preparation was then loaded onto the peptide column in the presence of calcium. Calpain was eluted with an EGTA-containing buffer. Using the two peptide-affinity columns connected in tandem, calpain was isolated with a high degree of purity, suitable for structural and mechanistic studies, i.e. as an 80/30-kDa heterodimer or in the form of dissociated monomers.

Effects of methylprednisolone on lesioned and uninjured mammalian spinal neurons: viability, ultrastructure, and network electrophysiology

An in vitro investigation was undertaken to provide information regarding the effectiveness of methylprednisolone sodium succinate (MPSS) as a treatment for the primary mechanical injury of spinal cord (SC) trauma. Exposure of uninjured mouse SC cells to MPSS for 24 h caused neuronal stress when the concentration exceeded 150 micrograms/mL; neuronal death occurred at concentrations above 600 micrograms/mL. The concentration range for MPSS protection of SC neurons subjected to a defined physical injury (laser microbeam transection of a primary dendrite 100 microns from the perikaryon) was very narrow: survival in the 30 micrograms/mL group differed significantly from the untreated control group (68.5% +/- 14.1 vs. 47.1% +/- 14.1), treatment with 20 or 60 micrograms/mL MPSS did not increase survival, and treatment with 100 micrograms/mL MPSS accelerated ultrastructural deterioration and increased the likelihood of death. Enhanced survival of lesioned neurons was observed when 30 micrograms/mL MPSS was applied within 15 min of dendrotomy but not when MPSS was administered 2 h after lesioning. Multimicroelectrode plate (MMEP) studies of SC network electrical activity indicated that MPSS associated readily with neuronal membranes. This finding was consistent with the hypothesis that MPSS may protect lesioned neurons by stabilizing damaged membranes, enhancing lesion resealing, and limiting the spread of ion-mediated damage. However, comparisons of neurite die-back 24 h after dendrotomy found no significant difference between MPSS-treated and control neurons. Application of 30 or 100 micrograms/mL MPSS increased the spontaneous burst activity of SC networks grown on MMEPs, however, there was no evidence that the increased excitability at these concentrations was the result of specific actions of MPSS on GABA or NMDA synapses.

Biosynthesis of prostaglandin D2 by motoneurons and dorsal horn microneurons: a biochemical and high resolution immunocytochemical study in chick spinal cord

Prostaglandin D2 is one of the major prostanoids formed from [14C]arachidonic acid by the central nervous system. The aim of the present study is to specify the prostaglandin D2 biosynthetic capacity in the chick spinal cord and to identify the cell type involved in this synthesis. A highly specific and sensitive enzyme immunoassay allowed us to demonstrate that the amount of newly formed prostaglandin D2 increases proportionally with the concentration of free arachidonic acid of either exogenous or endogenous origin and reaches concentration values ranging from 10(-9) to 10(-6) M. The sites of prostaglandin D2 synthesis were localized in Vibratome sections of spinal cord after incubation with antibodies raised against glutathione-independent prostaglandin D synthase; controls were performed with anti-glutathione-dependent prostaglandin D synthase antibodies and non-immune rabbit or goat serum. After immunoprocessing, electron microscope examination revealed that the specific immunoreactivity was confined to small neurons of laminae II and III in the dorsal horn and to motoneurons in the ventral horn of the spinal cord. The immunodeposits were associated with rough endoplasmic reticulum profiles distributed throughout the dorsal horn neurons or restricted to limited subsurface areas of perikarya and dendrites in motoneurons. Since the immunoreactive neurons in the dorsal horn were closely related to blood capillaries, prostaglandin D2 may be suspected to play a role in the regulation of the microcirculation. The accumulation of prostaglandin D synthase in motoneuron areas facing astrocytic membrane stacks suggests that prostaglandin D2 could interact with astrocytic functions.

Calpain secreted by activated human lymphoid cells degrades myelin

Calpain secreted by lymphoid (MOLT-3, M.R.) or monocytic (U-937, THP-1) cell lines activated with PMA and A23187 degraded myelin antigens. The degradative effect of enzymes released in the extracellular medium was tested on purified myelin basic protein and rat central nervous system myelin in vitro. The extent of protein degradation was determined by SDS-PAGE and densitometric analysis. Various proteinase inhibitors were used to determine to what extent protein degradation was mediated by calpain and/or other enzymes. Lysosomal and serine proteinase inhibitors inhibited 20-40% of the myelin-degradative activity found in the incubation media of cell lines, whereas the calcium chelator (EGTA), the calpain-specific inhibitor (calpastatin), and a monoclonal antibody to m calpain blocked myelin degradation by 60-80%. Since breakdown products of MBP generated by calpain may include fragments with antigenic epitopes, this enzyme may play an important role in the initiation of immune-mediated demyelination.

Purification of mu-calpain by a novel affinity chromatography approach. New insights into the mechanism of the interaction of the protease with targets

A calmodulin-binding motif is a common structural feature of a number of calpain substrates (1). Since a calmodulin-like domain has been identified in both subunits of the calpain molecule, the proposal was made that the domain(s) would recognize the calmodulin-binding motifs of the substrates prior to the enzymatic modification by calpain. In keeping with the proposal, a successful attempt to purify mu-calpain from human erythrocytes was made by using an affinity chromatography approach in which the synthetic peptide C49, containing the calmodulin-binding domain of the plasma membrane Ca(2+)-ATPase, was coupled to a Sepharose matrix. The calmodulin-like domain of the catalytic subunit of human mu-calpain expressed in Escherichia coli was also retained by the C49-Sepharose column. Both mu-calpain and the calmodulin-like domain interacted with C49 in a Ca(2+)-dependent way and were eluted from the column by Ca(2+)-chelating agents. The finding confirmed the interaction between the calmodulin-binding domain of the plasma membrane Ca(2+)-ATPase and the calmodulin-like domain of mu-calpain. Experiments were performed to establish whether irreversibly inactivated mu-calpain or its expressed C-terminal portion containing the calmodulin-like domain could activate the hydrolysis of ATP by the plasma membrane Ca2+ pump, in keeping with evident ATPase stimulation of the same pump by calmodulin. A stimulation was observed, but it was much weaker than that induced by calmodulin.

Lipid alterations following impact spinal cord injury in the rat

A computer-controlled impactor was used to produce a severe spinal cord injury in the rat thoracic spinal cord. Cords were rapidly frozen in situ at 5, 15, 30, and 60 min and 6, 12, and 24 h postinjury. Control cords were noninjured cords from animals having undergone a laminectomy and allowed to recover for 90 min postlaminectomy. The cords were assayed for alterations in lipid metabolism. Specifically, there were rapid increases in prostaglandin F2 alpha and thromboxane, with a peak increase in thromboxane levels at 30 min. Prostaglandin F2 alpha levels peaked at 15 min with levels remaining nearly constant for 12 h. There were no detectable changes in phospholipid levels, although diacylglycerol levels and free fatty acid levels were increased. Total free fatty acids were increased at 12 and 24 h postinjury by 2.3- and 3.2-fold over control levels, respectively. Arachidonic acid levels were not significantly elevated at early time points, however, these early time points correspond to elevated eicosanoid synthesis and this may account for the lack of early detectable increases in arachidonic acid. After 6 h postinjury, arachidonic acid levels were 20-fold greater than control levels and remained elevated at 24 h. There were minimal decreases in cholesterol and no decrease in either choline or ethanolamine plasmalogen levels. These results suggest a rapid turnover of arachidonic acid following spinal cord injury with a concomitant increase in vasoconstrictive eicosanoid synthesis. The lack of changes in major membrane constituents suggests the mechanisms may not involve general membrane degradation, but an over-stimulation of phospholipase A2-linked membrane receptors.

The effects of methylprednisolone and the ganglioside GM1 on acute spinal cord injury in rats

Recent clinical trials have reported that methylprednisolone sodium succinate (MP) or the monosialic ganglioside GM1 improves neurological recovery in human spinal cord injury. Because GM1 may have additive or synergistic effects when used with MP, the authors compared MP, GM1, and MP+GM1 treatments in a graded rat spinal cord contusion model. Spinal cord injury was caused by dropping a rod weighing 10 gm from a height of 1.25, 2.5, or 5.0 cm onto the rat spinal cord at T-10, which had been exposed via laminectomy. The lesion volumes were quantified from spinal cord Na and K shifts at 24 hours after injury and the results were verified histologically in separate experiments. A single dose of MP (30 mg/kg), given 5 minutes after injury, reduced 24-hour spinal cord lesion volumes by 56% (p = 0.0052), 28% (p = 0.0065), and 13% (p > 0.05) in the three injury-severity groups, respectively, compared to similarly injured control groups treated with vehicle only. Methylprednisolone also prevented injury-induced hyponatremia and increased body weight loss in the spine-injured rats. When used alone, GM1 (10 to 30 mg/kg) had little or no effect on any measured variable compared to vehicle controls; when given concomitantly with MP, GM1 blocked the neuroprotective effects of MP. At a dose of 3 mg/kg, GM1 partially prevented MP-induced reductions in lesion volumes, while 10 to 30 mg/kg of GM1 completely blocked these effects of MP. The effects of MP on injury-induced hyponatremia and body weight loss were also blocked by GM1. Thus, GM1 antagonized both central and peripheral effects of MP in spine-injured rats. Until this interaction is clarified, the authors recommend that MP and GM1 not be used concomitantly to treat acute human spinal cord injury. Because GM1 modulates protein kinase activity, protein kinases inhibit lipocortins, and lipocortins mediate anti-inflammatory effects of glucocorticoids, it is proposed that the neuroprotective effects of MP are partially due to anti-inflammatory effects and that GM1 antagonizes the effects of MP by inhibiting lipocortin. Possible beneficial effects of GM1 reported in central nervous system injury may be related to the effects on neural recovery rather than acute injury processes.

A model for compression trauma: pressure-induced injury in cell cultures

An increase in pressure up to 15 atm was used to condense the cellular membrane of cells in culture thereby eliciting a mechanical-like trauma. This trauma is similar to a compression-like spinal cord injury or brain injury. The cells used in this study were ROC-1 oligodendroglia, N1E-115 neuroblastoma, and human umbilical vein endothelial (HUVE) cells. Total fatty acid (FA) release and release of lactate dehydrogenase (LDH) into the extracellular medium were used as indices of cellular trauma. Pressure-induced FA release, dependent on pressure and pressure duration, occurred with all cell types. The level of pressure needed to cause the greatest increase in FA levels was 10 atm for ROC-1 cells (3 min duration), 15 atm for N1E-115 cells (3 min duration), and 15 atm for HUVE cells (10 min duration). With each cell type, the released FA were reacylated or metabolized between 10 and 30 min of recovery. Following a 12- to 24-h recovery period, N1E-115 and HUVE cells release more FA, indicating that the initial perturbation of the membrane was not fully reversible. LDH levels were significantly increased in both the N1E-115 and HUVE cultures following 24 h of recovery. This efflux of LDH indicates irreversible membrane damage, suggesting that the trauma may be irreversible at longer recovery times.

Affinity labelling of the Ca(2+)-activated neutral proteinase (calpain) in intact human platelets

Two irreversible calpain inhibitors, benzyloxycarbonyl (Cbz)-Leu-Leu-Tyr-Ch2F and Cbz-Leu-Leu-Tyr-CHN2, were shown earlier [Anagli, Hagmann and Shaw (1991) Biochem. J. 274, 497-502] to penetrate intact platelets and to inactivate calpain. This permitted an evaluation of certain functions attributed to this proteinase. For example, in platelets pretreated with these inhibitors, talin and actin-binding protein were protected from subsequent degradation when the Ca2+ level was raised. On the other hand, additional properties of stimulated platelets attributed to calpain remained unaffected by this treatment, and such hypotheses may be dismissed. Radioiodinated inhibitors permitted confirmation of the labelling of calpain by the procedures used. Although Cbz-Leu-Leu-Tyr-CHN2 is more effective in vitro than the corresponding fluoromethyl ketone, we now show that the latter penetrates more readily. These two inhibitors, and two additional ones, t-butyloxycarbonyl-Val-Lys(Cbz)-Leu-Tyr- CHN2 and Cbz-Leu-Tyr-CH2F, have been radioiodinated to permit a comparison of their intracellular labelling patterns in activated platelets. Calpain is the major target of all four inhibitors. Although they are closely related peptide structures, variations with respect to the labelling of additional proteins were observed. These were minor in the case of the peptidyl diazomethyl ketones, but were major in the case of the fluoromethyl ketones. However, in contrast to calpain, this labelling was neither time-dependent nor Ca(2+)-dependent. Radiolabelling and cellular fractionation studies were used to localize active calpain during platelet activation. Calpain appears to be activated in the cytosol and translocated to the membrane or cytoskeletal sites.

Differential production of prostaglandins D2 and E2 and of an unusual prostanoid by chick spinal cord and meninges in vitro

In order to specify the source of locally synthesized prostaglandin (PG) E2 which is able to saturate the large class of low affinity PGE2 receptors in chick spinal cord, bioconversion of [1-14C]arachidonic acid into prostanoids was studied in homogenates of chick spinal cord and meninges first without addition of exogenous glutathione (GSH). Homogenates of spinal cord produced 14C-labeled PGE2, PGD2 and PGF2 alpha. Homogenates of meninges accumulated much larger amounts of [14C]PGE2 than spinal cord and surprisingly a 14C-labeled arachidonate metabolite referred to as compound Y. Compound Y generation, which was inhibited by indomethacin and enhanced by esculetin, was therefore mediated through the cyclooxygenase pathway. The fact that no labeled compound Y was detected in homogenates incubated with [3H]PGD2 or [3H]PGE2 indicated that compound Y was not a degradation product of PGs. Secondly, after addition of exogenous GSH, 14C-labeled compound Y was totally converted into [14C]PGE2. The compound Y which is converted into PGFs after a strong reduction with NaBH4 and into PGE2 after a mild reduction with GSH-hemin system or SnCl2 was therefore assumed to be a 15 hydroperoxy-PGE2 (15 HP-PGE2). These results suggest that PGE2 can be synthesized in meninges either by the classical isomerization of PGH2 or by isomerization of PGG2 followed by a GSH-sensitive reaction.

Blood flow and electrolytes in spinal cord ischemia

The contribution of reoxygenation-reperfusion injury to ischemic brain damage has been clearly demonstrated but not in the spinal cord. To evaluate this phenomenon in spinal cord ischemia, we measured spinal cord blood flow (SCBF) by [14C]iodoantipyrine and electrolytes in rabbits after 10 or 40 min ischemia followed by 30 min or 4 days recirculation. Ischemia for 10 or 40 min reduced blood flow in the lower lumbar segments L5-L7 (30 ml/100 g/min) to 5 and 10% of control. After 30 min of recirculation moderate hyperemia (25-40% above control) was observed in segments L5-L7 which was not related to the degree of functional impairment. Na+, water, and Ca2+ increased and K+ decreased after 40 min ischemia, but were unchanged after 10 min ischemia. Recirculation for 30 min after 40 min of ischemia resulted in a progressive rise in Ca2+ which correlated with irreversible spinal cord injury.

Oxygen radicals: common mediators of neurotoxicity

The inherent biochemical, anatomical and physiological characteristics of the brain make it especially vulnerable to insult. Specifically, some of these characteristics such as myelin and a high energy requirement provide for the introduction of free radical-induced insult. Recently, the biochemistry of free radicals has received considerable attention. It also has become increasingly apparent that many drug and chemical-induced toxicities may be evoked via free radicals and oxidative stress. Major points addressed in this work are the regulation of neural free radical generation by antioxidants and protective enzymes, xenobiotic-induced disruption of cerebral redox status, and specific examples of neurotoxic agent-induced alterations in free radical production as measured by the fluorescent probe dichlorofluorescein. This article considers the thesis that free radical mechanisms may contribute significantly to the properties of several diverse neurotoxic agents and proposes that excess production of free radicals may be common phenomena of neurotoxicity.

Evaluation of traumatic spinal cord edema using evoked potentials recorded from the spinal epidural space. An experimental study in the rat

Spinal cord evoked potentials (SCEP) elicited by simultaneous distal tibial and sural nerve stimulation were continuously recorded from the epidural space at the T9 and T12 levels of urethane anaesthetized rats before and after a unilateral incision (about 3 mm deep and 5 mm long) in the right dorsal horn of the T10-11 segments. The changes in SCEP were correlated with the increase in spinal cord water content measured 5 h after injury. In addition, the influence of serotonin (5-HT) in mediating such changes was explored using a pharmacological approach. The changes in SCEP immediately after injury correlated well with development of spinal cord edema measured 5 h after injury. Thus, the maximal negative peak (MNP) amplitude of SCEP decreased by an average of 64.0% immediately after injury and the water content of the spinal cord was increased from 71.6% (controls) to 77.6% 5 h after injury. Pretreatment with p-CPA (a serotonin synthesis inhibitor) prevented the initial decrease of the MNP amplitude and also the increase of water content (72.5%). On the other hand, pretreatment with cyproheptadine (a 5-HT2 receptor antagonist) enhanced both the initial decrease of the MNP amplitude as well as the increase of water content (81.3%). The results show a good correlation between changes of SCEP immediately after injury and the magnitude of spinal cord edema (r = 0.9) measured 5 h after injury. The findings reveal a major role of serotonin in mediating early changes of SCEP and later development of spinal cord edema and demonstrate a prognostic value of early SCEP recordings in predicting the final outcome of traumatic spinal cord injuries.

Mapping of the canine lumbosacral spinal cord neurons by Nauta method at the end of the early phase of paraplegia induced by ischemia and reperfusion

The Nauta impregnation method was used to map the neuronal changes in the canine lumbosacral segments following ischemia and reperfusion. The early perikaryal changes ensuing during the first phase after 30 min of thoracic aorta cross-clamping alone or followed by 30 min of reperfusion were mapped. During the second phase (one to six postischemic reperfusion days) the dendritic, preterminal and synaptic degeneration developed. The influence of 30 min cross-clamping immediately followed by perfusion fixation is characterized by the occurrence of flocculent argyrophilic clusters in the cytoplasm of middle-sized and large neurons of L3-S1 segments. Declamping of the thoracic aorta followed by 30 min of reperfusion basically modifies the susceptibility of lumbosacral neurons to Nauta impregnation promoting somatic and dendritic argyrophilia mainly of small (less than 15 microns) neurons, localized mostly in the fifth, sixth and seventh layers, respectively. This early appearing somatic and dendritic argyrophilia is not abolished by a pretreatment of sections with acetone in which cholesterol and its esters are highly soluble, or chloroform-methanol which extracts total lipid. After 24 h of reperfusion the somatic and dendritic argyrophilia is lost but the first signs of drop-like degeneration are detected in all but three superficial dorsal horn layers. At the end of the third reperfusion day, an atypical form of bouton degeneration was found, consisting of massive occurrence of enlarged (greater than 4 microns) boutons encircled by a clear halo. Laminar distribution of enlarged degenerating boutons coincides with laminar quantitative distribution of small argyrophilic neurons detected 30 min after reperfusion. The basic orientation of the many terminal fibres attached to enlarged boutons suggests that they belong to the axons localized mainly in the lateral and anterior columns. Despite a dense argyrophilic network pervading the gray matter of lumbosacral segments only pale shadows of middle-sized and large neurons were found at the end of the sixth reperfusion day and neither somatic nor vessel wall argyrophilia could be detected. All animals surviving one, three and six days postoperatively suffered from fully developed paraplegia.

Disruption of cellular elements and water in neurotoxicity: studies using electron probe X-ray microanalysis

Regulation of elements and water in nerve cells is a complex, multifaceted process which appears to be vulnerable to neurotoxic events. However, much of our knowledge concerning the potential role of elements in nerve cell injury is limited by the relatively gross level of corresponding analyses. If we are to confirm and understand the proposed role, more precise and detailed information is needed. As indicated in this commentary, research employing electron probe microanalysis and digital X-ray imaging has begun to provide this necessary information. Recent EPMA studies of nerve and glial cells in the peripheral and central nervous systems have shown that each cell type and their corresponding morphologic compartments exhibit unique distributions of elements and water. The use of microprobe analysis has allowed us to document precisely how elements and water redistribute in morphological compartments of damaged nerve cells. Accumulating evidence from EPMA studies suggests that, rather than being an epiphenomenon, intracellular changes in diffusible elements might mediate the functional and structural consequences of neurotoxic insult. It is also evident from this research that elements other than Ca might play a pertinent role in the injury response and that changes in intraneuronal elemental composition might develop according to a specific temporal pattern, e.g., transection-induced sequential alterations in axonal K, Na, Cl, and Ca. Therefore, rather than conducting end-point studies, longitudinal investigations are necessary to define the sequential pattern of elemental perturbation associated with a given neurotoxic event. Such research can also help identify the role of individual elements in the injury response. Future microprobe studies should be combined with measurements of ion levels (e.g., using fura-2 or ion selective electrodes) to provide a comprehensive and dynamic view of elemental deregulation. In addition, parallel biochemical studies should be performed to determine mechanisms of elemental disruption and possible biochemical and metabolic consequences of this disruption. Although evidence presented in this commentary suggests that each type of neurotoxic event produces a characteristic pattern of decompartmentalization, further work is necessary to confirm this possibility. Finally, based on a presumed involvement of elements in nerve injury, efforts are currently underway in several laboratories to develop appropriate pharmacological therapies for certain chemical- and trauma-induced neuropathological conditions (Dretchen et al., 1986; El-Fawal et al., 1989; Beattie et al., 1989).(ABSTRACT TRUNCATED AT 400 WORDS)

Increased 5-hydroxytryptamine immunoreactivity in traumatized spinal cord. An experimental study in the rat

The possibility that serotonin (5-hydroxytryptamine, 5-HT) is involved in the early tissue reactions occurring in spinal cord trauma was examined in a rat model using an immunocytochemical technique. The injury was made in the form of a 5-mm long and 2.5-mm wide lesion of the right dorsal horn at the level of T10-11. Injured rats, pretreated with the 5-HT synthesis blocking agent, p-chlorophenyl alanine (p-CPA) were compared with untreated injured controls and the animals were allowed to survive for 5 h. The distribution of 5-HT was examined in proximal and distal cross- sections of the cord, located 2 and 5 mm away from the injury. Normal rats showed immunoreactive material in nerve cell processes and in a few nerve cell bodies of the ventral horns. The trauma to the spinal cord caused a marked increase in 5-HT immunoreactivity in the segments located 2 mm proximal and distal to the injury, particularly in the ipsilateral ventral horn. The segment located 5 mm distal to the lesion showed a similar increase in immunoreactivity but it was apparently less pronounced in the corresponding proximal segment. Treatment with p-CPA markedly reduced the trauma-induced increase in 5-HT immunoreactivity in all the segments. These immunohistochemical findings were in line with the changes in the contents of 5-HT measured biochemically in corresponding spinal cord segments. At the onset of the trauma to the spinal cord 5-HT is thus present in the tissue, mainly in the form of 5-HT-containing nerve cell processes.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of p-chlorophenylalanine on microvascular permeability changes in spinal cord trauma. An experimental study in the rat using 131I-sodium and lanthanum tracers

The possibility that serotonin can take part in the initiation of the increased microvascular permeability occurring in a spinal cord trauma was investigated in a rat model with 131I-sodium and lanthanum as tracers. We influenced the serotonin content in the tissue pharmacologically by treating animals with a serotonin synthesis inhibitor, p-chlorophenylalanine (p-CPA), before the production of the injury and compared the results with injured, untreated controls. A small incision was made in the dorsal horn of the lower thoracic cord. It caused a progressive extravasation of 131I-sodium in the damaged segment, measured after 1, 2 and 5 h. Rostral and caudal segments also showed a significant but lower accumulation of 131I-sodium. Lanthanum added to the fixative was used as an ionic tracer detectable by electron microscopy. The endothelial cells of microvessels removed from the perifocal region after 5 h showed a marked increase in the number of lanthanum-filled vesicles. Many endothelial cells had a diffuse penetration of the tracer into the cytoplasm and the basement membrane. However, the tight junctions usually remained closed to lanthanum. Pretreatment with p-CPA markedly reduced the extravasation of 131I-sodium measured at 5 h in the traumatized cord. At the cellular level, the endothelial vesicles filled with lanthanum approached the condition of uninjured animals. The diffuse infiltration of lanthanum into endothelial cells and its spread into the basement membrane of the vascular wall were usually absent. Our results indicate that serotonin plays a role in the initiation of the increased microvascular permeability which occurs in spinal cord injuries.

Edema formation and cellular alterations following spinal cord injury in the rat and their modification with p-chlorophenylalanine

The possibility that serotonin can modify the early pathological sequences occurring in spinal cord trauma was investigated in a rat model. To that end we took advantage of the possibility of influencing serotonin pharmacologically by treating animals with a serotonin synthesis inhibitor, p-chlorophenylalanine (p-CPA) before the production of the injury and compared the results with injured, untreated controls. A unilateral incision was made into the dorsal horn of the lower thoracic cord (about 2.5 mm deep, 4.5 mm long) and the rats were allowed to survive up to 5 h after the trauma. The injured region from untreated animals showed macroscopically at that time a pronounced swelling and the water content had increased by 3.5% as compared to intact controls. The segments rostral and caudal to the lesion also exhibited a profound increase in water content. Light microscopy revealed a significant expansion of the spinal cord as compared to controls. The swelling was most pronounced in the gray matter on the injured side. Electron microscopy showed distorted neurons, swollen astrocytes and extracellular edema in the gray matter in and around the primary lesion. There was also a sponginess in the surrounding white matter with disruption of myelin, collapsed axons and widened periaxonal spaces. Pretreatment of the rats with p-CPA significantly reduced the swelling of the injured spinal cord and there was no visible expansion. The ipsilateral edema in the central gray matter was considerable less pronounced as compared to that in untreated animals. The increase in water content was less than 1% in these animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Early accumulation of serotonin in rat spinal cord subjected to traumatic injury. Relation to edema and blood flow changes

Changes in the concentration of serotonin (5-hydroxytryptamine) in the early period after a focal traumatic injury to rat spinal cord were determined and related to the formation of edema and alterations in blood flow. A unilateral, 5-mm-long and 3-mm-deep traumatic injury located 2 mm from the midline was created in the T10-11 segment of the cord. Five hours after the injury the serotonin concentration in the traumatized segment had increased more than 100% compared with controls. There was also a progressive increase in water content of the traumatized segment measured 1-5 h after the injury. On the other hand, the spinal cord blood flow showed a progressive decrease to about 35% of its initial value at 5 h. Pretreatment with p-chlorophenylalanine, a serotonin synthesis inhibitor, impeded the elevation in water content measured 5 h after the trauma. The spinal cord blood flow remained close to normal values and the increase in serotonin was absent. Our results show that trauma to the rat spinal cord will induce changes in the serotonin concentration of the tissue and that the associated formation of edema and blood flow alterations can be alleviated in serotonin depleted rats. Obviously, serotonin plays a significant role in the pathophysiology of traumatic injury of rat spinal cord.

Intracellular calcium and neurotoxic events

Calcium is important in many intracellular regulatory processes. However, the maintenance of low levels of this cation within the cytosol is essential for maintenance of cell viability, in view of the large concentration gradient of ionic calcium across the plasma membrane. The expenditure of energy is needed to maintain intracellular calcium concentration [Ca2+]i at normal levels. In addition, the integrity of the limiting membrane is also vital for this function. Thus, any disruption of membrane characteristics or of mitochondrial anabolic processes may lead to deleterious levels of [Ca2+]i. The toxicity of a wide range of unrelated agents may, therefore, be in part due to elevation of cytosolic calcium. This general event may synergize with the more selective harmful properties of a compound, thus adversely affecting cell metabolism. The capacity now exists to measure levels of [Ca2+]i in isolated cells or organelles such as synaptosomes. The use of such in vitro models can be of value in the evaluation of the neurotoxic potential of compounds. This method, in conjunction with the use of pharmacological agents known to act at specific sites, and with the use of radioactive calcium in translocation studies, also has utility in the delineation of the biochemical mode of action of neurotoxic agents.