Guinea Pig Spinal Cord Research Articles

Paranodal Myelin Damage after Acute Stretch in Guinea Pig Spinal Cord

Mechanical injury causes myelin disruption and subsequent axonal conduction failure in the mammalian spinal cord. However, the underlying mechanism is not well understood. In mammalian myelinated axons, proper paranodal myelin structure is crucial for the generation and propagation of action potentials. The exposure of potassium channels at the juxtaparanodal region due to myelin disruption is thought to induce outward potassium currents and inhibit the genesis of the action potential, leading to conduction failure. Using multimodal imaging techniques, we provided anatomical evidence demonstrating paranodal myelin disruption and consequent exposure and redistribution of potassium channels following mechanical insult in the guinea pig spinal cord. Decompaction of paranodal myelin was also observed. It was shown that paranodal demyelination can result from both an initial physical impact and secondary biochemical reactions that are calcium dependent. 4-Aminopyridine (4-AP), a known potassium channel blocker, can partially restore axonal conduction, which further implicates the role of potassium channels in conduction failure. We provide important evidence of paranodal myelin damage, the role of potassium channels in conduction loss, and the therapeutic value of potassium blockade as an effective intervention to restore function following spinal cord trauma.

The effects of fasudil on the permeability of the rat blood–brain barrier and blood–spinal cord barrier following experimental autoimmune encephalomyelitis

Dysfunction of the blood–brain barrier (BBB) and blood–spinal cord barrier (BSCB) is a primary characteristic of multiple sclerosis (MS). We evaluated the protective effects of fasudil, a selective ROCK inhibitor, in a model of experimental autoimmune encephalomyelitis (EAE) that was induced by guinea-pig spinal cord. In addition, we studied the effects of fasudil on BBB and BSCB permeability. We found that fasudil partly alleviated EAE-dependent damage by decreasing BBB and BSCB permeability. These results provide rationale for the development of selective inhibitors of Rho kinase as a novel therapy for MS.

Effect of honey bee venom on Lewis rats with experimental allergic encephalomyelitis as regards to changes of GABA and glutamate

Multiple sclerosis (MS) is a progressive, neurodegenerative disease of central nervous system (CNS). Experimental allergic encephalomyelitis (EAE) is a widely accepted animal model for MS. Honey bee venom (Apis mellifera) contains a variety of different low and high molecular weight peptides and proteins including melittin, apamin, adolapin, mast cell degranulating peptide and phospholipase A2. Bee venom (BV) also could exert anti- inflammatory and antinociceptive effects on the inflammatory reactions. Glotamic acid and γ-aminobutyric acid (GABA) are among neurotransmitters of central nervous system and participated in excitatory and inhibitory processes. In EAE the amount of GABA reduces and the level of glutamate will increase. Tracing them in brain could useful in monitoring the influences of drugs. In this research, hematoxylin and eosin methods for inflammation, ELISA to study tumor necrosis factor-alpha (TNF-α) and HPLC, to study the amount of GABA and glutamate were used for assessment. In this study, we showed that in EAE level of GABA has reduced and the amount of glutamate has increased and bee venom decreases pathological changes and the level of serum TNF-α, and level of glutamate and increases the level of GABA in EAE rats induced by spinal cord of guinea pig.

Novel Model to Investigate Blast Injury in the Central Nervous System

Blast-induced neurotrauma (BINT) is a common injury modality associated with the current war efforts and increasing levels of terrorist activity. Exposure to the primary blast wave generated by explosive devices causes significant neurological deficits and is responsible for many of the war-related pathologies. Despite research efforts, the mechanism of injury is still poorly understood. To this end, we have established a novel ex vivo model for the direct observation and quantification of BINT at the tissue level. The model provides a quantifiable and reproducible method to illustrate the mechanism of BINT. Isolated sections of guinea pig spinal cord white matter were exposed to a supersonic shockwave using a blast generator with small-scaled explosives. The blast wave impact with isolated tissue was observed using focused shadowgraphy with a high-speed camera recording at 90,000 fps. Concurrently, functional deficits were measured by monitoring the production of compound action potentials using a double sucrose gap-recording chamber. Additionally, anatomical deficits were measured after blast exposure with a dye exclusion assay to visualize axonal membrane permeability. Our findings demonstrate that direct exposure to the blast wave compressed nervous tissue at a rate of 60 m/sec and led to significant functional deficits. Damage to the isolated spinal cord was marked by increased axonal permeability, suggesting rapid compression from the shockwave-generated high strain rates that resulted in membrane disruption. The model provides new insight into the mechanism of BINT and permits direct observation that may contribute to the development of appropriate treatment regimens.

Acrolein induces myelin damage in mammalian spinal cord

Myelin damage can lead to the loss of axonal conduction and paralysis in multiple sclerosis and spinal cord injury. Here, we show that acrolein, a lipid peroxidation product, can cause significant myelin damage in isolated guinea pig spinal cord segments. Acrolein-mediated myelin damage is particularly conspicuous in the paranodal region in both a calcium dependent (nodal lengthening) and a calcium-independent manner (paranodal myelin splitting). In addition, paranodal protein complexes can dissociate with acrolein incubation. Degraded myelin basic protein is also detected at the paranodal region. Acrolein-induced exposure and redistribution of paranodal potassium channels and the resulting axonal conduction failure can be partially reversed by 4-AP, a potassium channel blocker. From this data, it is clear that acrolein is capable of inflicting myelin damage as well as axonal degeneration, and may represent an important factor in the pathogenesis in multiple sclerosis and spinal cord injury.

The therapeutic effects of fluoxetine on experimental autoimmune encephalomylitis

Objective To investigate whether fluoxetine has therapeutic effect of clinical score and brain derived neurotrophic factor (BDNF) expression in serum of experimental autoimmune encephalomyelitis (EAE)model. Methods Rats were randomly divided into solvent control group (n=6) ,model control group ( n= 10)and fluoxetine group ( n= 10). The EAE model was prepared by injecting guinea pig spinal cord homogenate subcutaneously. The clinical score was daily measured according to the sign and symptoms of rats in the behavior examination. The serum BDNF level was measured by EL1SA. Results 1. Except for the solvent control group,the first sign of EAE(Piloerection) was detected on 4th day after immunization of rats from both model control group and fluoxetine group,then EAE rats had distal tail weakness on 8th day, and gradually developed into completely tail paralysis and limb paralysis. EAE rats' clinical score reached the peak on 16th day after immunization. 2. The clinical score of fluoxetine group became scientifically lower than model group since 18th day after immunization ( Fluoxetine group :3.27 ± 0. 33; Model control group :4.66 ± 0. 55, P ＜ 0. 05 ). 3. Compared with the model control group,fluoxetine did not significantly increase the expression of serum BDNF in EAE model ( Fluoxetine group:62.27 ± 0.43; Model control group :61.67 ± 0.85, P ＞ 0.05 ). Conclusion Fluoxetine reduced the clinical score of EAE since 18th day after immunization,which indicates fluoxetine could promote the recovery of neurological function in EAE rats. BDNF may not contribute to protective effect of fluoxetine in EAE animal. Key words: Experimental autoimmune encephalomylitis; Fluoxetine; Brain-derived neurotrophic factor; Rats

A transversely isotropic constitutive model of excised guinea pig spinal cord white matter

Narrowing of the spinal canal generates an amalgamation of stresses within the spinal cord parenchyma. The tissue’s stress state cannot be quantified experimentally; it must be described using computational methods, such as finite element analysis. The objective of this research was to propose a compressible, transversely isotropic constitutive model, an augmentation of the isotropic Mooney–Rivlin hyperelastic strain energy function, to describe the guinea pig spinal cord white matter. Model parameters were derived from a combination of inverse finite element analysis on transverse compression experiments and least squared error analysis applied to quasi-static longitudinal tensile tests. A comparison of the residual errors between the predicted response and the experimental measurements indicated that the transversely isotropic constitutive law that incorporates an offset stretch reduced the error by a factor of four when compared to other commonly used models.

Compression Induces Acute Demyelination and Potassium Channel Exposure in Spinal Cord

Crush to the mammalian spinal cord leads to primary mechanical damage followed by a series of secondary biomolecular events. The chronic outcomes of spinal cord injuries have been well detailed in multiple previous studies. However, the initial mechanism by which constant displacement injury induces conduction block is still unclear. We therefore investigated the anatomical factors that may directly contribute to electrophysiological deficiencies in crushed cord. Ventral white matter strips from adult guinea pig spinal cord were compressed 80%, either briefly or continuously for 30 min. Immunofluorescence imaging and coherent anti-Stokes Raman spectroscopy (CARS) were used to visualize key pathological changes to ion channels and myelin. Compression caused electrophysiological deficits, including compound action potential (CAP) decline that was injury-duration-dependent. Compression further induced myelin retraction at the nodes of Ranvier. This demyelination phenomenon exposed a subclass of voltage-gated potassium channels (K(v)1.2). Application of a potassium channel blocker, 4-aminopyridine (4-AP), restored the CAP to near pre-injury levels. To further investigate the myelin detachment phenomenon, we constructed a three-dimensional finite element model (FEM) of the axon and surrounding myelin. We found that the von Mises stress was highly concentrated at the paranodal junction. Thus, the mechanism of myelin retraction may be associated with stress concentrations that cause debonding at the axoglial interface. In conclusion, our findings implicate myelin disruption and potassium channel pathophysiology as the culprits causing compression-mediated conduction block. This result highlights a potential therapeutic target for compressive spinal cord injuries.

CHITOSAN REPAIRS DAMAGED SPINAL CORD

Richard Borgens and his colleagues from the Center for Paralysis Research at the Purdue School of Veterinary Medicine have a strong record of inventing therapies for treating nerve damage. From Ampyra, which improves walking in multiple sclerosis patients, to a spinal cord stimulator for spinal injury victims, Borgens has had a hand in developing therapies that directly impact patients and their quality of life. Another therapy that is currently undergoing testing is the use of polyethylene glycol (PEG) to seal and repair damaged spinal cord nerve cells. By repairing the damaged membranes of nerve cells, Borgens and his team can restore the spinal cord's ability to transmit signals to the brain. However, there is one possible clinical drawback: PEG's breakdown products are potentially toxic. Is there a biodegradable non-toxic compound that is equally effective at targeting and repairing damaged nerve membranes? Borgens teamed up with physiologist Riyi Shi and chemist Youngnam Cho, who pointed out that some sugars are capable of targeting damaged membranes. Could they find a sugar that restored spinal cord activity as effectively as PEG (p. 1513)?Having initially tested mannose and found that it did not repair spinal cord nerve membranes, Cho decided to test a modified form of chitin, one of the most common sugars that is found in crustacean shells. Converting chitin into chitosan, Cho isolated a segment of guinea pig spinal cord, compressed a section, applied the modified chitin and then added a fluorescent dye that could only enter the cells through damaged membranes. If the chitosan repaired the crushed membranes then the spinal cord tissue would be unstained, but if the chitosan had failed, the spinal cord would be flooded with the fluorescent dye. Viewing a section of the spinal cord under the microscope, Cho was amazed to see that the spinal cord was completely dark. None of the dye had entered the nerve cells. Chitosan had repaired the damaged cell membranes.Next, Cho tested whether a dose of chitosan could prevent large molecules from leaking from damaged spinal cord cells. Testing for the presence of the colossal enzyme lactate dehydrogenase (LDH), Borgens admits he was amazed to see that levels of LDH leakage from chitosan-treated spinal cord were lower than from undamaged spinal cords. The sugar had repaired membranes not only at the compression site but also at other sites where the cell membranes were broken due to handling. And when the duo tested for the presence of harmful reactive oxygen species (ROS), released when the membranes of ATP-generating mitochondria are damaged, they found that ROS levels also fell after applying chitosan to the damaged tissue: chitosan repairs mitochondrial membranes as well as the nerve cell membranes.But could chitosan restore the spinal cord's ability to transmit electrical signals to the brain through a damaged region? Measuring the brain's response to nerve signals generated in a guinea pig's hind leg, the duo saw that the signals were unable to reach the brain through a damaged spinal cord. However, 30 min after injecting chitosan into the rodents, the signals miraculously travelled again to the animals' brains. Chitosan was able to repair the damaged spinal cord so that it could carry signals from the animal's body to its brain.Borgens is extremely excited by this discovery that chitosan is able to locate and repair damaged spinal cord tissue and is even more enthusiastic by the prospect that nanoparticles of chitosan could also target delivery of neuroprotective drugs directly to the site of injury, ‘giving us a dual bang for our buck,’ says Borgens.

Chitosan produces potent neuroprotection and physiological recovery following traumatic spinal cord injury

Chitosan, a non-toxic biodegradable polycationic polymer with low immunogenicity, has been extensively investigated in various biomedical applications. In this work, chitosan has been demonstrated to seal compromised nerve cell membranes thus serving as a potent neuroprotector following acute spinal cord trauma. Topical application of chitosan after complete transection or compression of the guinea pig spinal cord facilitated sealing of neuronal membranes in ex vivo tests, and restored the conduction of nerve impulses through the length of spinal cords in vivo, using somatosensory evoked potential recordings. Moreover, chitosan preferentially targeted damaged tissues, served as a suppressor of reactive oxygen species (free radical) generation, and the resultant lipid peroxidation of membranes, as shown in ex vivo spinal cord samples. These findings suggest a novel medical approach to reduce the catastrophic loss of behavior after acute spinal cord and brain injury.

Modeling Blast Induced Neurotrauma in Isolated Spinal Cord White Matter

Blast-induced neurotrauma (BINT) is a common injury associated with the present military conflicts. Exposure to the shock-wave produced from exploding ordnances leads to significant neurological deficits throughout the brain and spinal cord. Prevention and treatment of this injury requires an appropriate understanding of the mechanisms governing the neurological response. Here, we present a novel ex-vivo BINT model where an isolated section of guinea pig spinal cord white matter is exposed to the shock-wave produced from a small scale explosive event. Additionally, we define the relationship between shock-wave impact, tissue deformation and resulting anatomical and functional deficits associated with BINT. Our findings suggest an inverse relationship between the magnitude of the shock-wave overpressure and the degree of functional deficits using a double sucrose gap recording chamber. Similar correlations are drawn between overpressure and degree of anatomical damage of neuronal processes using a dye-exclusion assay. The following approach is expected to significantly contribute to the detection, mitigation and eventual treatment of BINT.

Polyethylene Glycol Enhances Axolemmal Resealing following Transection in Cultured Cells and inEx VivoSpinal Cord

The integrity of the neuronal membrane is critical for its function as well as survival, and ineffective repair of damaged membranes may be one of the key factors underlying the neuronal degeneration and overall functional loss that occurs after spinal cord injury and traumatic brain injury. Previously, we showed that polyethylene glycol (PEG) can reseal axonal membranes following compression in isolated guinea pig spinal cord white matter. We now report that 10 mM PEG can also significantly enhance membrane resealing following transection in the clinically relevant conditions of low extracellular Ca(2+) and low temperature. Such beneficial effects were demonstrated both functionally, through membrane potential measured by double sucrose gap apparatus, and anatomically, through horseradish peroxidase and tetramethyl rhodamine dextran dye exclusion assays. We further noted that axons with small diameters preferentially benefited from PEG-mediated axolemmal resealing. Using atomic force microscopy, we further showed that PEG can effectively reduce neuronal membrane surface tension. We hypothesize that PEG may promote axolemmal resealing by increasing membrane line tension and reducing membrane tension, thus creating conditions more favorable to membrane resealing. In summary, these studies suggest that PEG is effective under the clinically relevant conditions of low Ca(2+) and temperature, and thus has the potential to be used in combination with other more established interventions in spinal cord and traumatic brain injury.

Modular double sucrose gap apparatus for improved recording of compound action potentials from rat and mouse spinal cord white matter preparations

Compound action potential (CAP) recording is a powerful tool for studying the conduction properties and pharmacology of axons in multi-axonal preparations. The sucrose gap technique improves CAP recording by replacing the extracellular solution between the recording electrodes with a non-conductive sucrose solution to minimize extracellular shunting. The double sucrose gap (DSG), conferring similar advantages at the stimulation site, has been extensively used on guinea pig spinal cord white matter (WM) in vitro. Establishing the DSG methodology for WM preparations from smaller animals such as rats and mice is appealing due to their extensive use in basic and translationally oriented research. Here we describe a versatile modular DSG apparatus with rubber membrane separation of the compartments, suitable for WM strips from rat and mouse spinal cord. The small volumes of compartments (<0.1 ml) and the air-tight design allow perfusion rates of 0.5–1 ml/min with faster refreshment rates compared to commonly used 2–3 ml/min and larger compartments, providing economical usage of expensive pharmacological drugs. Our improved DSG design is particularly efficient for uncovering slower conducting, higher threshold CAP components, as demonstrated by recordings of C-wave (non-myelinated axons) in rat dorsal WM. In myelin-deficient Shiverer mice with genetically dysmyelinated axons, our DSG apparatus recordings revealed a multi-peak C-wave without preceding faster components. The improved stimulation and recording with our DSG apparatus, lowering the range of required stimulus intensities and reducing the artifact interference with recorded CAPs provide for critical technical advantages that allow for more detailed analysis of CAPs in relatively short preparations.

Novel Potassium Channel Blocker, 4-AP-3-MeOH, Inhibits Fast Potassium Channels and Restores Axonal Conduction in Injured Guinea Pig Spinal Cord White Matter

We have demonstrated that 4-aminopyridine-3-methanol (4-AP-3-MeOH), a 4-aminopyridine derivative, significantly restores axonal conduction in stretched spinal cord white-matter strips and shows no preference in restoring large and small axons. This compound is 10 times more potent when compared with 4-AP and other derivatives in restoring axonal conduction. Unlike 4-AP, 4-AP-3-MeOH can restore axonal conduction without changing axonal electrophysiological properties. In addition, we also have confirmed that 4-AP-3-MeOH is indeed an effective blocker of I(A) based on patch-clamp studies using guinea pig dorsal root ganglia cells. Furthermore, we have also provided the critical evidence to confirm the unmasking of potassium channels following mechanical injury. Taken together, our data further supports and implicates the role of potassium channels in conduction loss and its therapeutic value as an effective target for intervention to restore function in spinal cord trauma. Furthermore, due to its high potency and possible low side effect of impacting electrophysiological properties, 4-AP-3-MeOH is perhaps the optimal choice in reversing conduction block in spinal cord injury compared with other derivatives previously reported from this group.

Chronic caffeine treatment attenuates experimental autoimmune encephalomyelitis induced by guinea pig spinal cord homogenates in Wistar rats

Dysfunction of adenosinergic systems has been implicated in the development of multiple sclerosis in humans and experimental autoimmune encephalomyelitis (EAE) in animals. Caffeine, a non-selective antagonist of adenosine receptors, has been shown to provide protection against myelin oligodendroglia glycoprotein (MOG)-induced EAE in mice. In this study, we showed that chronic caffeine similarly imparts neuroprotection against EAE induced in rats by guinea pig spinal cord homogenates (GPSCH). GPSCH-induced EAE is characterized by extensive tissue inflammation with a typical chronic disease course. We showed that caffeine decreases the incidence of EAE and attenuates EAE pathology at behavioral, histological (inflammatory cell infiltration and demyelination) and neurochemical (expression of inflammatory cytokines) levels. The attenuation of GPSCH-induced pathology by chronic caffeine treatment was observed at doses of 10 and 30 mg/kg and during both peak and recovery phases of EAE. Furthermore, it was showed that chronic treatment with caffeine up-regulated A1 receptor and TGF-β mRNAs and suppressed interferon-γ mRNA in EAE rats. Together with previous reports, our data demonstrates that chronic treatment with caffeine exerts a neuroprotective effect against EAE, possibly through an A 1 receptor-mediated shift from Th1 to Th2 cell function, and provides a neurobiological basis for epidemiological investigation into the possible relationship between caffeine consumption and development of multiple sclerosis in humans.

Spinal cord hydrolysate ameliorate immunological reaction in experimental allergic encephalomyelitis.

The aim of this study was to use the hydrolysate of pig spinal cord proteins to induce oral tolerance in the animal model of sclerosis multiplex - experimental allergic encephalomyelitis. The female Lewis rats were fed with hydrolysate of pig spinal cord proteins in two doses for one week before immunization, which was induced by injection of guinea pig spinal cord homogenate. At the peak of clinical symptoms (the 13th day post immunization) the rats were sacrificed and the spleen removed. Splenocytes were suspended in a culture medium and placed in microculture plates. The cells were stimulated with homogenate. The cells were cultured for seven days. Proliferation of splenocytes was estimated by means of methyl-3H thymidine incorporation. In supernatants of cultures of splenocytes the level of cytokines INF-gamma, IL-10, IL-4, and TGF-gamma was measured. It was demonstrated that homogenate-induced splenocytes of hydrolysate-fed rats gave rise to low proliferation as compared to the controls used. The IFN-gamma was inhibited in hydrolysate-fed animals. The hydrolysate of pig spinal cord proteins has a modulatory effect on the immune reaction, particularly on the orally-induced antigen-specific modulation of autoimmune response.

Critical roles of decompression in functional recovery of ex vivo spinal cord white matter

The correlations between functional deficits, the magnitude of compression, and the role of sustained compression during traumatic spinal cord injury remain largely unknown. Thus, the functional outcome of this type of injury with or without surgical intervention is rather unpredictable. To elucidate how severity and duration of compression affect cord function, the authors have developed a method to study electrophysiological characteristics and axonal membrane damage in white matter from guinea pig spinal cord. Ventral white matter strips isolated from adult guinea pigs were compressed by a compression rod at a level of either 60 or 80% and held briefly, for 30 minutes, or for 60 minutes. In half the experimental groups, a decompression phase consisting of probe withdrawal and 30 minutes of recovery was also applied. For all cord samples, functional response was continuously monitored through compound action potential (CAP) recording. In addition, axonal membrane damage was assessed by a horseradish peroxidase (HRP) exclusion assay. After 30 minutes of sustained compression at levels of 60 or 80%, a spinal cord decompression procedure caused a significant CAP recovery, with specimens reaching 97.5 +/- 6.84% (p < 0.05) and 56.2 +/- 6.14% (p < 0.05) of preinjury amplitude, respectively. After 60 minutes of compression, the amount of CAP recovery following the decompression stage was only 65.5 +/- 9.33% for 60% compression (p < 0.05) and 29.8 +/- 6.31% for 80% compression (p < 0.05). Unlike the CAP response, HRP uptake did not increase during sustained compression, and the data showed that HRP staining was primarily time dependent. The degree of axonal membrane damage is not exacerbated during sustained compression. However, the electrical conductivity of the cord white matter weakens throughout the duration of compression. Therefore, decompression is a viable procedure for preservation of neurological function following compressive injury.

Physiological abnormalities in experimental allergic encephalomyelitis (EAE): II. Correlation between clinical signs and vestibular hyperreactivity and other signs of brain-stem dysfunction in rats with EAE.

12 Lewis rats were inoculated with a guinea pig spinal cord tissue preparation. They developed experimental allergic encephalomyelitis (EAE) after 12-14 days manifested by weight loss, tail flaccidity, ataxia, hind limb paresis or paralysis and urinary incontinence. Concomitantly with EAE, all animals developed vestibular hyperreactivity (VH) of canal and otolith reflexes. Other signs of brain-stem dysfunction were also observed: abducens paralysis, facial weakness, tachypnoe and mydriasis with defective pupillary light reflex. The vestibular and other abnormalities subsided with some delay after recovery from clinical EAE, whilst histological abnormalities were still present in the CNS.

Idazoxan attenuates spinal cord injury by enhanced astrocytic activation and reduced microglial activation in rat experimental autoimmune encephalomyelitis

Idazoxan, an imidazoline 2 receptor (I 2R) ligand, has been shown to protect against brain injury in several animal models of neurological disorders. In the present study we investigated the effect of idazoxan on experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis. EAE was induced by immunizing Wistar rats with guinea pig spinal cord homogenates emulsified in CFA, followed by daily treatment of idazoxan (0, 0.5 mg/kg, 1.5 mg/kg, 4.5 mg/kg, i.p, bid) for 10 days. The results showed that the treatment of idazoxan (1.5 mg/kg and 4.5 mg/kg) significantly decreased the incidence and alleviated inflammatory cell infiltration and demyelination in spinal cords and cerebral cortex. Furthermore, the protective effect of idazoxan on EAE was associated with the enhanced astrocytic activation and attenuated microglial activation and with the subsequent down-regulated expression of proinflammatory cytokines IL-12p40 and IFN-γ and up-regulated expression of anti-inflammatory cytokines IL-10 and TGF-β 1. Thus, the daily treatment of the I 2R ligand idazoxan for 10 days attenuates EAE pathology by differential modulation of astrocytic and microglial activations, raising a possibility that the I 2R ligand may be a novel strategy for treating EAE.

Large naturally-produced electric currents and voltage traverse damaged mammalian spinal cord

BackgroundImmediately after damage to the nervous system, a cascade of physical, physiological, and anatomical events lead to the collapse of neuronal function and often death. This progression of injury processes is called "secondary injury." In the spinal cord and brain, this loss in function and anatomy is largely irreversible, except at the earliest stages. We investigated the most ignored and earliest component of secondary injury. Large bioelectric currents immediately enter damaged cells and tissues of guinea pig spinal cords. The driving force behind these currents is the potential difference of adjacent intact cell membranes. For perhaps days, it is the biophysical events caused by trauma that predominate in the early biology of neurotrauma.ResultsAn enormous (≤ mA/cm2) bioelectric current transverses the site of injury to the mammalian spinal cord. This endogenous current declines with time and with distance from the local site of injury but eventually maintains a much lower but stable value (< 50 μA/cm2).The calcium component of this net current, about 2.0 pmoles/cm2/sec entering the site of damage for a minimum of an hour, is significant. Curiously, injury currents entering the ventral portion of the spinal cord may be as high as 10 fold greater than those entering the dorsal surface, and there is little difference in the magnitude of currents associated with crush injuries compared to cord transection. Physiological measurements were performed with non-invasive sensors: one and two-dimensional extracellular vibrating electrodes in real time. The calcium measurement was performed with a self-referencing calcium selective electrode.ConclusionThe enormous bioelectric current, carried in part by free calcium, is the major initiator of secondary injury processes and causes significant damage after breach of the membranes of vulnerable cells adjacent to the injury site. The large intra-cellular voltages, polarized along the length of axons in particular, are believed to be associated with zones of organelle death, distortion, and asymmetry observed in acutely injured nerve fibers. These data enlarge our understanding of secondary mechanisms and provide new ways to consider interfering with this catabolic and progressive loss of tissue.