Effect of impact trauma on neurotransmitter and nonneurotransmitter amino acids in rat spinal cord

Acute ampakines increase voiding function and coordination in a rat model of SCI

Neurogenic bladder dysfunction causes urological complications and reduces the quality of life in persons with spinal cord injury (SCI). Glutamatergic signaling via AMPA receptors is fundamentally important to the neural circuits controlling bladder voiding. Ampakines are positive allosteric modulators of AMPA receptors that can enhance the function of glutamatergic neural circuits after SCI. We hypothesized that ampakines can acutely stimulate bladder voiding that has been impaired due to thoracic contusion SCI. Adult female Sprague-Dawley rats received a unilateral contusion of the T9 spinal cord (n = 10). Bladder function (cystometry) and coordination with the external urethral sphincter (EUS) were assessed 5 d post-SCI under urethane anesthesia. Data were compared to responses in spinal-intact rats (n = 8). The 'low-impact' ampakine CX1739 (5, 10, or 15 mg/kg) or vehicle (2-hydroxypropyl-beta-cyclodextrin [HPCD]) was administered intravenously. The HPCD vehicle had no discernible impact on voiding. In contrast, following CX1739, the pressure threshold for inducing bladder contraction, voided volume, and the interval between bladder contractions were significantly reduced. These responses occurred in a dose-dependent manner. We conclude that modulating AMPA receptor function using ampakines can rapidly improve bladder-voiding capability at subacute time points following contusion SCI. These results may provide a new and translatable method for therapeutic targeting of bladder dysfunction acutely after SCI.

Synaptic or Non-synaptic? Different Intercellular Interactions with Retinal Ganglion Cells in Optic Nerve Regeneration

Axons of adult neurons in the mammalian central nervous system generally fail to regenerate by themselves, and few if any therapeutic options exist to reverse this situation. Due to a weak intrinsic potential for axon growth and the presence of strong extrinsic inhibitors, retinal ganglion cells (RGCs) cannot regenerate their axons spontaneously after optic nerve injury and eventually undergo apoptosis, resulting in permanent visual dysfunction. Regarding the extracellular environment, research to date has generally focused on glial cells and inflammatory cells, while few studies have discussed the potentially significant role of interneurons that make direct connections with RGCs as part of the complex retinal circuitry. In this study, we provide a novel angle to summarize these extracellular influences following optic nerve injury as "intercellular interactions" with RGCs and classify these interactions as synaptic and non-synaptic. By discussing current knowledge of non-synaptic (glial cells and inflammatory cells) and synaptic (mostly amacrine cells and bipolar cells) interactions, we hope to accentuate the previously neglected but significant effects of pre-synaptic interneurons and bring unique insights into future pursuit of optic nerve regeneration and visual function recovery.

Comparative transcriptome analysis provides novel insights into the molecular mechanism of the silver carp (Hypophthalmichthys molitrix) brain in response to hypoxia stress

The brain of fish plays an important role in regulating growth and adapting to environmental changes. However, few studies have been performed to address the changes in gene expression profiles in fish brains under hypoxic stress. In the present study, silver carp (Hypophthalmichthys molitrix) were kept under hypoxic experimental conditions by using the method of natural oxygen consumption, which resulted in a significant decrease in malondialdehyde (MDA) and glutathione (GSH) content and superoxide dismutase (SOD) activity in the brain. In addition, RNA sequencing (RNA-Seq) was performed to analyze transcriptional regulation in the brains of silver carp under normoxia (control group), hypoxia, semi-asphyxia, and asphyxia conditions. The results of KEGG enrichment pathway analysis showed that the immune system, such as antigen processing and presentation, natural killer cell-mediated cytotoxicity, was enriched in the hypoxia group; the nervous system (e.g., "glutamatergic synapse"), signal transduction (e.g., "calcium signaling pathway"; "foxo signaling pathway"), and signaling molecules and interactions (e.g., "neuroactive ligand-receptor interaction") were enriched in the semi-asphyxia group; and signaling molecules and interactions (e.g., "neuroactive ligand-receptor interaction") were enriched in the asphyxia group. These results provide novel insights into the molecular regulatory mechanism of the fish brain coping with hypoxia stress.

GABAergic Mechanisms Can Redress the Tilted Balance between Excitation and Inhibition in Damaged Spinal Networks

Correct operation of neuronal networks depends on the interplay between synaptic excitation and inhibition processes leading to a dynamic state termed balanced network. In the spinal cord, balanced network activity is fundamental for the expression of locomotor patterns necessary for rhythmic activation of limb extensor and flexor muscles. After spinal cord lesion, paralysis ensues often followed by spasticity. These conditions imply that, below the damaged site, the state of balanced networks has been disrupted and that restoration might be attempted by modulating the excitability of sublesional spinal neurons. Because of the widespread expression of inhibitory GABAergic neurons in the spinal cord, their role in the early and late phases of spinal cord injury deserves full attention. Thus, an early surge in extracellular GABA might be involved in the onset of spinal shock while a relative deficit of GABAergic mechanisms may be a contributor to spasticity. We discuss the role of GABA A receptors at synaptic and extrasynaptic level to modulate network excitability and to offer a pharmacological target for symptom control. In particular, it is proposed that activation of GABA A receptors with synthetic GABA agonists may downregulate motoneuron hyperexcitability (due to enhanced persistent ionic currents) and, therefore, diminish spasticity. This approach might constitute a complementary strategy to regulate network excitability after injury so that reconstruction of damaged spinal networks with new materials or cell transplants might proceed more successfully.

GABA promotes survival and axonal regeneration in identifiable descending neurons after spinal cord injury in larval lampreys

The poor regenerative capacity of descending neurons is one of the main causes of the lack of recovery after spinal cord injury (SCI). Thus, it is of crucial importance to find ways to promote axonal regeneration. In addition, the prevention of retrograde degeneration leading to the atrophy/death of descending neurons is an obvious prerequisite to activate axonal regeneration. Lampreys show an amazing regenerative capacity after SCI. Recent histological work in lampreys suggested that GABA, which is massively released after a SCI, could promote the survival of descending neurons. Here, we aimed to study if GABA, acting through GABAB receptors, promotes the survival and axonal regeneration of descending neurons of larval sea lampreys after a complete SCI. First, we used in situ hybridization to confirm that identifiable descending neurons of late-stage larvae express the gabab1 subunit of the GABAB receptor. We also observed an acute increase in the expression of this subunit in descending neurons after SCI, which further supported the possible role of GABA and GABAB receptors in promoting the survival and regeneration of these neurons. So, we performed gain and loss of function experiments to confirm this hypothesis. Treatments with GABA and baclofen (GABAB agonist) significantly reduced caspase activation in descending neurons 2 weeks after a complete SCI. Long-term treatments with GABOB (a GABA analogue) and baclofen significantly promoted axonal regeneration of descending neurons after SCI. These data indicate that GABAergic signalling through GABAB receptors promotes the survival and regeneration of descending neurons after SCI. Finally, we used morpholinos against the gabab1 subunit to knockdown the expression of the GABAB receptor in descending neurons. Long-term morpholino treatments caused a significant inhibition of axonal regeneration. This shows that endogenous GABA promotes axonal regeneration after a complete SCI in lampreys by activating GABAB receptors.

Cyclopropyl-containing positive allosteric modulators of metabotropic glutamate receptor subtype 5

Positive allosteric modulators (PAMs) binding to the transmembrane (TM) domain of metabotropic glutamate receptor 5 (mGluR5) are promising therapeutic agents for psychiatric disorders and traumatic brain injury (TBI). Novel PAMs based on a trans-2-phenylcyclopropane amide scaffold have been designed and synthesized. Facilitating ligand design and allowing estimation of binding affinities to the mGluR5 TM domain was the novel computational strategy, site identification by ligand competitive saturation (SILCS). The potential protective activity of the new compounds was evaluated using nitric oxide (NO) production in BV2 microglial cell cultures treated with lipopolysaccharide (LPS), and the toxicity of the new compounds tested using a cell viability assay. One of the new compounds, 3a, indicated promising activity with potency of 30 μM, which is 4.5-fold more potent than its lead compound 3,3'-difluorobenzaldazine (DFB), and showed no detectable toxicity with concentrations as high as 1000 μM. Thus this compound represents a new lead for possible development as treatment for TBI and related neurodegenerative disorders.

Cochlear ablation effects on amino acid levels in the chinchilla cochlear nucleus

Inner ear damage can lead to hearing disorders, including tinnitus, hyperacusis, and hearing loss. We measured the effects of severe inner ear damage, produced by cochlear ablation, on the levels and distributions of amino acids in the first brain center of the auditory system, the cochlear nucleus. Measurements were also made for its projection pathways and the superior olivary nuclei. Cochlear ablation produces complete degeneration of the auditory nerve, which provides a baseline for interpreting the effects of partial damage to the inner ear, such as that from ototoxic drugs or intense sound. Amino acids play a critical role in neural function, including neurotransmission, neuromodulation, cellular metabolism, and protein construction. They include major neurotransmitters of the brain - glutamate, glycine, and γ-aminobutyrate (GABA) - as well as others closely related to their metabolism and/or functions - aspartate, glutamine, and taurine. Since the effects of inner ear damage develop over time, we measured the changes in amino acid levels at various survival times after cochlear ablation. Glutamate and aspartate levels decreased by 2weeks in the ipsilateral ventral cochlear nucleus and deep layer of the dorsal cochlear nucleus, with the largest decreases in the posteroventral cochlear nucleus (PVCN): 66% for glutamate and 63% for aspartate. Aspartate levels also decreased in the lateral part of the ipsilateral trapezoid body, by as much as 50%, suggesting a transneuronal effect. GABA and glycine levels showed some bilateral decreases, especially in the PVCN. These results may represent the state of amino acid metabolism in the cochlear nucleus of humans after removal of eighth nerve tumors, which may adversely result in destruction of the auditory nerve. Measurement of chemical changes following inner ear damage may increase understanding of the pathogenesis of hearing impairments and enable improvements in their diagnosis and treatment.

Cochlear damage affects neurotransmitter chemistry in the central auditory system

Tinnitus, the perception of a monotonous sound not actually present in the environment, affects nearly 20% of the population of the United States. Although there has been great progress in tinnitus research over the past 25 years, the neurochemical basis of tinnitus is still poorly understood. We review current research about the effects of various types of cochlear damage on the neurotransmitter chemistry in the central auditory system and document evidence that different changes in this chemistry can underlie similar behaviorally measured tinnitus symptoms. Most available data have been obtained from rodents following cochlear damage produced by cochlear ablation, intense sound, or ototoxic drugs. Effects on neurotransmitter systems have been measured as changes in neurotransmitter level, synthesis, release, uptake, and receptors. In this review, magnitudes of changes are presented for neurotransmitter-related amino acids, acetylcholine, and serotonin. A variety of effects have been found in these studies that may be related to animal model, survival time, type and/or magnitude of cochlear damage, or methodology. The overall impression from the evidence presented is that any imbalance of neurotransmitter-related chemistry could disrupt auditory processing in such a way as to produce tinnitus.

Neuronal release and successful astrocyte uptake of aminoacidergic neurotransmitters after spinal cord injury in lampreys

In contrast to mammals, the spinal cord of lampreys spontaneously recovers from a complete spinal cord injury (SCI). Understanding the differences between lampreys and mammals in their response to SCI could provide valuable information to propose new therapies. Unique properties of the astrocytes of lampreys probably contribute to the success of spinal cord regeneration. The main aim of our study was to investigate, in the sea lamprey, the release of aminoacidergic neurotransmitters and the subsequent astrocyte uptake of these neurotransmitters during the first week following a complete SCI by detecting glutamate, GABA, glycine, Hu and cytokeratin immunoreactivities. This is the first time that aminoacidergic neurotransmitter release from neurons and the subsequent astrocytic response after SCI are analysed by immunocytochemistry in any vertebrate. Spinal injury caused the immediate loss of glutamate, GABA and glycine immunoreactivities in neurons close to the lesion site (except for the cerebrospinal fluid-contacting GABA cells). Only after SCI, astrocytes showed glutamate, GABA and glycine immunoreactivity. Treatment with an inhibitor of glutamate transporters (DL-TBOA) showed that neuronal glutamate was actively transported into astrocytes after SCI. Moreover, after SCI, a massive accumulation of inhibitory neurotransmitters around some reticulospinal axons was observed. Presence of GABA accumulation significantly correlated with a higher survival ability of these neurons. Our data show that, in contrast to mammals, astrocytes of lampreys have a high capacity to actively uptake glutamate after SCI. GABA may play a protective role that could explain the higher regenerative and survival ability of specific descending neurons of lampreys.

Effects of cochlear ablation on amino acid levels in the rat cochlear nucleus and superior olive

Amino acids have important roles in the chemistry of the auditory system, including communication among neurons. There is much evidence for glutamate as a neurotransmitter from auditory nerve fibers to cochlear nucleus neurons. Previous studies in rodents have examined effects of removal of auditory nerve input by cochlear ablation on levels, uptake and release of glutamate in cochlear nucleus subdivisions, as well as on glutamate receptors. Effects have also been reported on uptake and release of γ-aminobutyrate (GABA) and glycine, two other amino acids strongly implicated in cochlear nucleus synaptic transmission. We mapped the effects of cochlear ablation on the levels of amino acids, including glutamate, GABA, glycine, aspartate, glutamine, taurine, serine, threonine, and arginine, in microscopic subregions of the rat cochlear nucleus. Submicrogram-size samples microdissected from freeze-dried brainstem sections were assayed for amino acid levels by high performance liquid chromatography. After cochlear ablation, glutamate and aspartate levels decreased by 2 days in regions receiving relatively dense innervation from the auditory nerve, whereas the levels of most other amino acids increased. The results are consistent with a close association of glutamate and aspartate with auditory nerve fibers and of other amino acids with other neurons and glia in the cochlear nucleus. A consistent decrease of GABA level in the lateral superior olive could be consistent with a role in some lateral olivocochlear neurons. The results are compared with those obtained with the same methods for the rat vestibular nerve root and nuclei after vestibular ganglionectomy.

Overexpression of BDNF increases excitability of the lumbar spinal network and leads to robust early locomotor recovery in completely spinalized rats

Strategies to induce recovery from lesions of the spinal cord have not fully resulted in clinical applications. This is a consequence of a number of impediments that axons encounter when trying to regrow beyond the lesion site, and that intraspinal rearrangements are subjected to. In the present study we evaluated (1) the possibility to improve locomotor recovery after complete transection of the spinal cord by means of an adeno-associated (AAV) viral vector expressing the neurotrophin brain-derived neurotrophic factor (BDNF) in lumbar spinal neurons caudal to the lesion site and (2) how the spinal cord transection and BDNF treatment affected neurotransmission in the segments caudal to the lesion site. BDNF overexpression resulted in clear increases in expression levels of molecules involved in glutamatergic (VGluT2) and GABAergic (GABA, GAD65, GAD67) neurotransmission in parallel with a reduction of the potassium-chloride co-transporter (KCC2) which contributes to an inhibitory neurotransmission. BDNF treated animals showed significant improvements in assisted locomotor performance, and performed locomotor movements with body weight support and plantar foot placement on a moving treadmill. These positive effects of BDNF local overexpression were detectable as early as two weeks after spinal cord transection and viral vector application and lasted for at least 7 weeks. Gradually increasing frequencies of clonic movements at the end of the experiment attenuated the quality of treadmill walking. These data indicate that BDNF has the potential to enhance the functionality of isolated lumbar circuits, but also that BDNF levels have to be tightly controlled to prevent hyperexcitability.

Regulation of nitric oxide generation by up-regulated arginase I in rat spinal cord injury

Recently, arginase is suggested to regulate nitric oxide production by competing with nitric oxide synthase for the same substrate, L-arginine, in experimental asthma. We investigated the role of arginase and its relationship to nitric oxide production after spinal cord injury. Rats were subjected to laminectomy and complete transection of their spinal cords (injury group) or laminectomy only (sham group). In the injury group, arginase I was increased in the macrophages at the transection edge, and the peak was observed 48 h after spinal cord injury. However, nitric oxide production decreased significantly in the injury group despite increased nitric oxide synthase2 mRNA expression compared with the sham group. We also demonstrated the reduction in L-arginine concentrations, which was inversely associated with changes in arginase activity. Therefore, arginase appeared to regulate nitric oxide production by consuming L-arginine. The regulation of arginase activity and L-arginine levels may improve nitroxidative stress and reduce tissue damage in spinal cord injury.

Adaptations in glutamate and glycine content within the lumbar spinal cord are associated with the generation of novel gait patterns in rats following neonatal spinal cord transection

After spinal cord transection, the generation of stepping depends on neurotransmitter systems entirely contained within the local lumbar spinal cord. Glutamate and glycine likely play important roles, but surprisingly little is known about how the content of these two key neurotransmitters changes to achieve weight-bearing stepping after spinal cord injury. We studied the levels of glutamate and glycine in the lumbar spinal cord of spinally transected rats. Rats (n = 48) received spinal cord transection at 5 days of age, and 4 weeks later half were trained to step using a robotic treadmill system and the remaining half were untrained controls. Analyses of glutamate and glycine content via high-performance liquid chromatography showed training significantly raised the levels of both neurotransmitters in the lumbar spinal cord beyond normal. The levels of both neurotransmitters were significantly correlated with the ability to perform independent stepping during training. Glutamate and glycine levels were not significantly different between Untrained and Normal rats or between Trained and Untrained rats. There was a trend for higher expression of VGLUT1 and GLYT2 around motor neurons in Trained versus Untrained rats based on immunohistochemical analyses. Training improved the ability to generate stepping at a range of weight support levels, but normal stepping characteristics were not restored. These findings suggested that the remodeling of the lumbar spinal circuitry in Trained spinally transected rats involved adaptations in the glutamatergic and glycinergic neurotransmitter systems. These adaptations may contribute to the generation of novel gait patterns following complete spinal cord transection.

Metabotropic glutamate receptor-mediated signaling in neuroglia

Metabotropic glutamate (mGlu) receptors are G-protein-coupled receptors, which include eight subtypes that have been classified into three groups (I-III) based upon sequence homology, signal transduction mechanism and pharmacological profile. Although most studied with regard to neuronal function and modulation, mGlu receptors are also expressed by neuroglia-including astrocytes, microglia and oligodendrocytes. Activation of mGlu receptors on neuroglia under both physiologic and pathophysiologic conditions mediates numerous actions that are essential for intrinsic glial cell function, as well as for glial-neuronal interactions. Astrocyte mGlu receptors play important physiological roles in regulating neurotransmission and maintaining neuronal homeostasis. However, mGlu receptors on astrocytes and microglia also serve to modulate cell death and neurological function in a variety of pathophysiological conditions such as acute and chronic neurodegenerative disorders. The latter effects are complex and bi-directional, depending on which mGlu receptor sub-types are activated.

Role of taurine on acid secretion in the rat stomach

Background

Taurine has chemical structure similar to an inhibitory neurotransmitter, γ-aminobutyric acid (GABA). Previous studies on GABA in the stomach suggest GABAergic neuron is involved in acid secretion, but the effects of taurine are poor understood.

Methods

The effects of taurine on acid secretion, signal transduction, and localization of taurinergic neurons were determined in the rat stomach using everted whole stomach, RIA kit and immunohistochemical methods.

Results

We used antibodies against taurine-synthesizing enzyme, cysteine sulfuric acid decarboxylase (CSAD), and taurine. CSAD- and taurine-positive cells were found in the muscle and mucosal layers. Distributions of CSAD- and taurine-positive cells in both mucosal and muscle layers were heterogeneous in the stomach. Taurine at 10^-9~10^-4 M induced acid secretion, and the maximum secretion was at 10^-5 M, 1.6-fold higher than the spontaneous secretion. Taurine-induced acid secretion was completely inhibited by bicuculline and atropine but not by cimetidine, proglumide, or strychnine. Atropine and tetrodotoxin (TTX) completely inhibited the acid secretion induced by low concentrations of taurine and partially inhibited induced by high concentrations. Verapamil, a calcium blocker agent, inhibited acid output elicited by taurine. We assumed all Ca²⁺ channels involved in the response to these secretagogues were equally affected by verapamil. Intracellular cAMP (adenosine 3', 5'-monophosphat) in the stomach significantly increased with taurine treatment in a dose-dependent manner. High correlation (r=0.859, p < 0.001) of taurine concentrations with cAMP was observed.

Conclusions

Our results demonstrated for the first time in taurine-induced acid secretion due to increase intracellular calcium may act through the A type of GABA receptors, which are mainly located on cholinergic neurons though cAMP pathway and partially on nonneuronal cells in the rat stomach.

Metabotropic glutamate receptors as targets for multipotential treatment of neurological disorders

Glutamate is a major excitatory neurotransmitter in the CNS that is involved in numerous cellular functions, including cell death and survival. Metabotropic glutamate receptors (mGluR) are G-protein coupled receptors that have been classified into three groups on the basis of signal transduction pathways and pharmacological profiles. Group I, II, and III mGluRs are found on cell types within and peripheral to the CNS, including neurons, microglia, astrocytes, oligodendrocytes, T- and B-cell lymphocytes, osteoblasts, hepatocytes, and endothelial cells, among others. These receptors have a number of effects on cells that can influence outcome after trauma, including reducing neuronal and oligodendroglial cell death, inflammation, and endothelial permeability. Thus, mGluRs are a promising multipotential therapeutic approach. Because the pathology of CNS trauma and neurodegeneration is multifactorial (including, for example, oxidative stress, mitochondrial breakdown, and inflammation), therapies that serve to modulate multiple pathophysiological pathways may prove more effective than those directed at a single target. This review examines the multipotential therapeutic utility of mGluR modulation in acute and chronic injury and neurodegeneration.

Comparative neuroprotective effect of sodium channel blockers after experimental spinal cord injury

Spinal cord injury (SCI) results in loss of function below the lesion. Secondary injury following the primary impact includes a number of biochemical and cellular alterations leading to tissue necrosis and cell death. Influx of Na(+) ions into cells has been postulated to be a key early event in the pathogenesis of secondary traumatic and ischemic central nervous system injury. Previous studies have shown that some voltage-sensitive sodium channel blockers provide powerful neuroprotection. The purpose of the present study was to compare the neuroprotective effect of three sodium channel blockers-mexiletine, phenytoin and riluzole--after SCI. Ninety rats were randomly and blindly divided into five groups of 18 rats each: sham-operated group, trauma group (bolus injection of 1 mL physiological saline intraperiteonally [i.p.]), mexiletine treatment group (80 mg/kg, i.p.), phenytoin treatment group (200 mg/kg, i.p.) and riluzole treatment group (8 mg/kg, i.p.). Twenty-four hours after injury, the rats were killed for determination of spinal cord water content and malondialdehyde (MDA) levels. Motor function scores of six rats from each group were evaluated weekly for six weeks. Then the rats were killed for histopathological assessment. Although all the treatment groups revealed significantly lower MDA levels and spinal cord edema than the trauma group (p<0.05), the riluzole and mexiletine treatment groups were better than the phenytoin treatment group. In the chronic stage, riluzole and mexiletine treatment achieved better results for neurobehavioral and histopathological recovery than phenytoin treatment. In conclusion, all the tested Na(+) blockers had a neuroprotective effect after SCI; riluzole and mexiletine were superior to phenytoin.

Preemptive analgesia with lidocaine prevents Failed Back Surgery Syndrome

Failed Back Surgery Syndrome (FBSS) is commonly encountered in pain-treatment settings in the United States. We tested whether potential key factors in this syndrome, such as extracellular concentrations of excitatory amino acids (EAAs), are increased in the dorsal horn by synaptic release due to unintentional stretch and/or deformation/compression/transection of dorsal spinal structures during surgery. We hypothesized that pharmacological nerve block as a form of preemptive analgesia prior to any insult to dorsal root neurons will prevent an abnormally high increase in extracellular concentrations of EAAs in the dorsal horn and ultimately the establishment of central sensitization during back surgery. The L4 and L5 dorsal roots were cut bilaterally near the spinal cord to provide an adequate model to test for preemptive analgesia. Amino acid concentrations were measured by dorsal horn microdialysis sampling; EAAs aspartate and glutamate were significantly increased by 80% and 65% respectively, as were other amino acids compared to sham control values. Topical application of 1% Lidocaine, a voltage-gated Na(+) channel blocker, for 10 min prior to L4 and L5 bilateral dorsal rhizotomy (BDR) significantly attenuated the increase in EAA concentrations such that their values were not different from sham controls. Behavioral tests demonstrated significant hindlimb mechanical allodynia after BDRs that was significantly attenuated by Lidocaine pretreatment. Thus, Lidocaine pretreatment could offer a safe measure for prevention of chronic pain for back surgical procedures if given by intramuscular injection, topical administration onto spinal nerves and/or the dorsal spinal surface during surgical procedures that include nerve entrapment release, intervertebral disc modification and laminectomies.

Acute alterations of glutamate, glutamine, GABA, and other amino acids after spinal cord contusion in rats

Spinal cord injury (SCI) leads to an alteration of energetic metabolism. As a consequence, glutamate, glutamine, aspartate and other important amino acids are altered after damage, leading to important disregulation of the neurochemical pathways. In the present study, we characterized the acute-phase changes in tissue concentration of amino acids involved in neurotransmitter and non-neurotransmitter actions after SCI by contusion in rats. Animals were submitted to either laminectomy or SCI by contusion and sacrificed at 2, 4, 8, and 12 h after lesion, for the analysis of tissue amino acids by HPLC. Results showed that both aspartate and glutamate contents diminished after SCI, while glutamine concentrations raised, however, the sum of molar concentrations of glutamate plus glutamine remained unchanged at all time points. GABA concentrations increased versus control group, while glycine remained unchanged. Finally, citrulline levels increased by effect of SCI, while taurine-increased only 4 h after lesion. Results indicate complex acute-phase changes in amino acids concentrations after SCI, reflecting the different damaging processes unchained after lesion.

Different effect of locomotor exercise on the homogenate concentration of amino acids and monoamines in the rostral and caudal lumbar segments of the spinal cord in the rat

STUDY DESIGN

The effect of long-term (4 weeks) moderate locomotor exercise on segmental distribution of glutamate (Glu), aspartate, gamma-aminobutyric acid, glycine (Gly), serotonin and noradrenaline in the spinal cord of adult rats was investigated.

OBJECTIVES

In light of the data showing modulation of some neurotransmitters in the low-lumbar segments of the rat due to physical exercise, our aim was to establish how segmentally specific is this effect with respect to neuroactive amino acids and monoamines.

SETTING

Laboratory of Reinnervation Processes, Department of Neurophysiology, Nencki Institute of Experimental Biology, Warsaw, Poland.

METHODS

Amino acids and monoamines content was measured by means of HPLC in the whole tissue homogenate of the spinal cord in nonexercised and exercised rats.

RESULTS

Glu and Gly homogenate concentration was the highest among all tested compounds. There was an intersegmental rostro-caudal gradient of concentration of neuroactive amino acids and monoamines, progressing caudally. Exercise modified this gradient exerting opposite effect on their concentration of amino acids and monoamines in the rostral and caudal lumbar segments.

CONCLUSION

Locomotor exercise leads to neurochemical remodeling of the spinal cord, which is differently manifested in the rostral and caudal lumbar segments of the spinal cord.

Synaptogenesis and amino acid release from long term embryonic rat spinal cord neuronal culture using tissue culture inserts

In the present study, using tissue culture inserts (TCI) coupled with a primary spinal cord neuronal culture, we characterize a new perfusion system, which permits continuous perfusate collection from cultured neurons. Primary spinal cord neurons were isolated from the lumbar portion of E14 spinal cords of Sprague-Dawley rats, plated on TCI and fed with DMEM/B27/10% FBS. At 1-4 weeks after isolation the development of synapses and neurotransmitter phenotype in cultured neurons was verified using immunofluorescence. A time-dependent development of synapses (Syn) was seen with a dense Syn-positive network identified at 3-4 weeks after plating. A sub-population of plated neurons (35-40%) showed GABA immunoreactivity and expressed NMDAR1 receptor. To measure neurotransmitter release, a chamber accommodating TCI was constructed permitting perfusion of the insert across the membrane. To evoke amino acid release from cultured neurons, NMDA (10 mmol/l) was added into the perfusion buffer. Stimulation with NMDA evoked a significant GABA (4050 +/- 950%) and glutamate release (130 +/- 42%) during first 10 min after exposure. In control non-stimulated cells no significant changes were measured. These data show that by using TCI it is possible to maintain embryonic spinal cord neurons for an extended period and that this system may represent a simple tool to identify neurotransmitter and/or peptides associated with a specific population of cultured brain and/or spinal cord neurons.

Allodynia after acute intrathecal morphine administration in a patient with neuropathic pain after spinal cord injury

IMPLICATIONS

Acute intrathecal administration of relatively small doses of opioids may precipitate neuropathic pain and allodynia in those with spinal cord injury.

Pathophysiological activity in rat dorsal horn neurones in segments rostral to a chronic spinal cord injury

As a sequel of complete spinal cord injury (SCI), patients often develop chronic pain which is perceived at or just below the level of the lesion. Likewise, in animal models of SCI, spontaneous and evoked pain-related behaviour can be observed. In the present study, the hypothesis was tested that pain related behaviour after SCI in animals is at least partly due to neuronal hyperactivity in spinal segments rostral to the site of injury. In rats with a chronic transected spinal cord, the impulse activity of single dorsal horn neurones was recorded in two locations: (1) directly rostrally adjacent to the lesion, and (2) 2-3 segments more rostrally. Cord transections were made either at the thoracic or at the lumbar level. Sham-operated rats and rats which underwent no surgical interventions served as controls. Compared with both controls, in SCI animals the background activity of the neurones had a significantly higher level in both series. Often the activity showed a pathophysiological altered discharge pattern. Following SCI, there was a general increase in the mechanical responsiveness of neurones that were recorded 2-3 segments rostrally to the lesion. The results suggest that neuronal hyperactivity in spinal segments just rostral to the lesion may contribute to chronic spontaneous SCI pain. Further, there is some indication that the allodynia perceived in body regions near and above the level of the SCI may be due to increased responsiveness to weak stimuli of neurones located more rostrally to the lesion.

Changes in nitric oxide and expression of nitric oxide synthase in spinal cord after acute traumatic injury in rats

The aim of this study was to observe the time course of NO production and NOS expression in the spinal cord following acute traumatic injury. Rat spinal cord was injured by extradural static weight-compression, which resulted in an incomplete transverse spinal cord lesion with paralysis of the lower extremities. Using this model, measurement of NO by microdialysis and Griess reaction and histological and immunohistochemical examinations using polyclonal antibodies to nNOS and iNOS were performed from immediately to 14 days after injury. In injured cord, the amount of NO markedly increased immediately after injury and gradually decreased between 1 and 12 h after injury. A second wave of increase in NO level was observed at 24 h and 3 days after injury. Histologically, hematomas and necrotic changes were observed after injury and demyelination of nerve fibers increased with time in the compressed segment. Immunohistochemically, the number of cells with expression of nNOS was increased immediately to 12 h after injury. Expression of iNOS was observed from 12 h to 3 days after injury. These findings suggested that the initial maximal increase of NO production might be caused mainly by nNOS and that the second wave of increase in NO might be due mainly to iNOS.

Injured metamere and functional surgery of the tetraplegic upper limb

The size of injured metamere (IM) in tetraplegia exhibits a high variability that explains the different clinical presentations in patients who have the same neurologic level. Even when functional electrical stimulation is not planned, the lower motor neuron (LMN) integrity of paralyzed muscles must be evaluated, especially in patients with high-level tetraplegia. During the acute phase, detecting the size of the IM is important to prevent supination contracture and stiffness of the thumb and finger joints. When planning functional surgery, the LMN integrity of intrinsic muscles helps the surgeon adapt his surgical procedures. Assessing IM size must be integrated systematically into the evaluation of tetraplegic patients.

NBQX treatment improves mitochondrial function and reduces oxidative events after spinal cord injury

The purpose of this study was to examine the effects of inhibiting ionotropic glutamate receptor subtypes on measures of oxidative stress events at acute times following traumatic spinal cord injury (SCI). Rats received a moderate contusion injury and 15 min later were treated with one of two doses of 1,2,3,4-tetrahydro-6-nitro-2,3-dioxo-benzol[f]quinoxaline-7-sulfonamide disodium (NBQX), MK-801, or the appropriate vehicle. At 4 h following injury, spinal cords were removed and a crude synaptosomal preparation obtained to examine mitochondrial function using the MTT assay, as well as measures of reactive oxygen species (ROS), lipid peroxidation, and glutamate and glucose uptake. We report here that intraspinal treatment with either 15 or 30 nmol of NBQX improves mitochondrial function and reduces the levels of ROS and lipid peroxidation products. In contrast, MK-801, given intravenously at doses of 1.0 or 5.0 mg/kg, was without effect on these same measures. Neither drug treatment had an effect on glutamate or glucose uptake, both of which are reduced at acute times following SCI. Previous studies have documented that drugs acting on non-N-methyl-D-aspartate (NMDA) receptors exhibit greater efficacy compared to NMDA receptor antagonists on recovery of function and tissue sparing following traumatic spinal cord injury. The results of this study provide a potential mechanism by which blockade of the non-NMDA ionotropic receptors exhibit positive effects following traumatic SCI.

Topical bicuculline to the rat spinal cord induces highly localized allodynia that is mediated by spinal prostaglandins

The purpose of this study was to investigate the allodynic effect of bicuculline (BIC) given topically to the dorsal surface of the rat spinal cord, and to determine if spinal prostaglandins (PGs) mediate the allodynic state arising from spinal GABA(A)-receptor blockade. Male Sprague-Dawley rats (325-400 g) were anaesthetized with halothane and maintained with urethane for the continuous monitoring of blood pressure (MAP), heart rate (HR) and cortical electroencephalogram (EEG). A laminectomy was performed to expose the dorsal surface of the spinal cord. Unilateral application of BIC (0.1 microg in 0.1 microl) to the L5 or L6 spinal segment induced a highly localized allodynia (e.g. one or two digits) on the ipsilateral hind paw. Thus, hair deflection (brushing the hair with a cotton-tipped applicator) in the presence, but not absence of BIC, evoked an increase in MAP and HR, abrupt motor responses (MR; e.g. withdrawal of the hind leg, kicking, and/or scratching) on the affected side, and desynchrony of the EEG. BIC-allodynia was dose-dependent, yielding ED(50)'s (95% CI's) of 45 ng (31-65) for MAP; 68 ng (46-101) for HR and 76 ng (60-97) for MR. Allodynia was sustained for up to 2 h with repeated BIC application without any detectable change in the location or area of peripheral sensitization. Pretreatment with either the EP(1)- receptor antagonist, SC-51322, the cyclooxygenase (COX)-2 selective inhibitor, NS-398, or the NMDA-receptor antagonist, AP-7, inhibited BIC-allodynia in a dose-dependent manner. The results demonstrate: (a) BIC, applied to the dorsal surface of the spinal cord, induces highly localized allodynia; (b) this effect can be sustained with repeated BIC application; (c) it is evoked by NMDA-dependent afferent input; (d) spinal PGs are synthesized by constitutive COX-2 during BIC-allodynia; and (e) spinal PGs contribute to the abnormal processing of tactile input via spinal EP1-receptors.

Spinal taurine levels are increased 7 and 30 days following methylprednisolone treatment of spinal cord injury in rats

The amino acid taurine serves many functions in the nervous system serving as inhibitory neurotransmitter/neuromodulator, neurotrophin, antioxidant, and osmolyte. Taurine levels are increased following brain injury and glucocorticoid administration. Thus, the purpose of this study was to examine spinal taurine concentrations following spinal cord injury (SCI) and methylprednisolone (MP) treatment of SCI. A total of 44 adult male Sprague-Dawley rats were divided into control and lesion groups. Control rats received a T6 vertebral laminectomy while lesioned rats received a laminectomy followed by complete spinal transection. Half of the animals in each group received MP intravenously following sham-operation or SCI. Rats survived for 7 or 30 days and concentrations of taurine in spinal gray and white matter, in spinal segments both near and distant from the injury epicenter, were resolved by HPLC analysis. Taurine levels were increased 7 and 30 days following transection in spinal segments immediately adjacent to the lesion and were further elevated by MP treatment. No increases were seen in far rostral/caudal segments, and MP treatment alone had no effect on spinal taurine levels. These findings demonstrate that spinal injury results in increased taurine concentrations in spinal segments undergoing the greatest degree of cellular reactivity and tissue reorganization and that MP therapy potentiates these increases. These findings are significant in that they further characterize the effects of acute MP therapy in spinal tissue. Since taurine is thought to be involved in neuroprotection and/or regeneration following injury, the potentiation of taurine levels by MP treatment may relate to its therapeutic properties.

Pain following spinal cord injury

Chronic pain is an important problem following spinal cord injury (SCI) and is a major impediment to effective rehabilitation. The reported prevalence of chronic SCI pain is variable but averages 65% with around one third of these people rating their pain as severe. The mechanisms responsible for the presence of pain are poorly understood. However, evidence from clinical observations and the use of animal models of SCI pain suggests that a number of processes may be important. These include functional and structural plastic changes in the central nervous system following injury, with changes in receptor function and loss of normal inhibition resulting in an increased neuronal excitability. A number of specific types of SCI pain can be distinguished based on descriptors, location and response to treatment. Nociceptive pain can arise from musculoskeletal structures and viscera and neuropathic pain can arise from spinal cord and nerve damage. The role of psychological and environmental factors also needs to be considered. Accurate identification of these pain types will help in selecting appropriate treatment approaches. Current treatments employ a variety of pharmacological, surgical, physical and psychological approaches. However, evidence for many of the treatments in use is still limited. It is hoped that future research will identify effective treatment strategies that accurately target specific mechanisms.

Riluzole and methylprednisolone combined treatment improves functional recovery in traumatic spinal cord injury

The potential use of riluzole (a glutamate release inhibitor) alone or in combination with methyl-prednisolone (MP) in treating acute spinal cored injury (SCI) was examined. Rats received a contusion injury to the spinal cord using the NYU impactor and were treated with vehicle, riluzole (8 mg/kg), MP(30 mg/kg), or riluzole + MP at 2 and 4 h following injury. Animals continued to receive riluzole treatment (8 mg/kg) for a period of 1 week. The animals were then tested weekly for functional recovery using the BBB open field locomotor score. At the end of testing (6 weeks after injury), each spinal cord was examined for the amount of remaining tissue at the injury site and a myelination index was used to quantify remaining axons in the ventromedial white matter. In this study, only the combination treatment was found to significantly improve behavioral recovery as assessed using the BBB open field locomotor scale. In addition, the combination treatment promoted tissue sparing at the lesion epicenter, but had no clear effect on the index of myelination. The results of this study clearly demonstrate the potential beneficial effects of a combination approach in the treatment of traumatic SCI.

Riluzole improves measures of oxidative stress following traumatic spinal cord injury

Rats received a contusion injury to the spinal cord followed by treatment with riluzole (a glutamate release inhibitor, 8 mg/kg), methylprednisolone (MP 30 mg/kg) or both. At 4 h following injury, spinal cords were removed and synaptosomes prepared and examined using five measures of oxidative stress. Riluzole treatment was found to improve mitochondrial function, and enhance glutamate and glucose uptake. As expected, MP treatment was found to reduce lipid peroxidation, but also improved glutamate and glucose uptake. Interestingly, the combination treatment was found to be effective in improving all five measures of oxidative stress. The results of this study clearly demonstrate the potential beneficial effects of a combination approach in the treatment of oxidative stress events in traumatic spinal cord injury.

Effectiveness of preoperative administration of an N-methyl-D-aspartate antagonist to enhance cochlear neuron resistance to intraoperative traumatic stress: an experimental study

OBJECT

Cochlear neurons are inevitably exposed to traumatic stress during surgical removal of an acoustic neuroma; that event is an important cause of postoperative cochlear neuronal degeneration, with subsequent loss of spiral ganglion cells (SGCs). The object of this study was to investigate whether preoperative pharmacological treatment can enhance the resistance of cochlear neurons to the traumatic stress of surgery.

METHODS

Cochlear neuronal degeneration was induced in 17 rats by controlled compression of the cerebellopontine angle portion of the cochlear nerve. Dizocilpine maleate (MK-801; 10 mg/kg), an N-methyl-D-aspartate (NMDA) antagonist, was administered intraperitoneally to six of the 17 rats 30 minutes before compression occurred. Two weeks after compression, each rat was killed, and the numbers of SGCs in histological preparations of temporal bones were counted.

CONCLUSIONS

Spiral ganglion cells were more numerous in rats administered dizocilpine maleate (p < 0.03) than in rats that did not receive treatment, indicating that receptor-mediated glutamate neurotoxicity may participate in the pathogenesis of trauma-induced cochlear neuron death and that administration of an NMDA antagonist before surgery may protect the nerve from injury leading to hearing loss.

Alterations in AMPA receptor subunit expression after experimental spinal cord contusion injury

The AMPA-preferring subtype of ionotropic glutamate receptors (GluRs) is a hetero-oligomeric ion channel assembled from various combinations of four subunits: GluR1, GluR2, GluR3, and GluR4. Antagonists of these receptors can mitigate the effects of experimental spinal cord injury (SCI), indicating that these receptors play a significant role in pathophysiology after spinal trauma. We tested the hypothesis that SCI alters expression of AMPA receptors using a standardized thoracic weight-drop model of rat contusive spinal cord injury. AMPA receptor subunit expression was measured at 24 hr and at 1 month after SCI with quantitative Western blot analysis and in situ hybridization. GluR2 protein levels were preferentially reduced near the injury site 24 hr after SCI. This reduction persisted at 1 month. At a cellular level, a significant decrease in both GluR2 and GluR4 mRNA was found in spared ventral motor neurons adjacent to the injury site and distal to it, with other AMPA subunit mRNAs maintained at control levels. In contrast, only GluR1 mRNA was decreased in the sympathetic preganglionic neurons of the intermediolateral horn. These results suggest population-specific and long-lasting changes in neuronal AMPA receptor composition, which may alter response to glutamate after SCI. These alterations may contribute not only to acute neuropathological consequences of injury, but they may also be partially responsible for the altered functional state of preserved tissue seen chronically after SCI.

Apoptosis following spinal cord injury in rats and preventative effect of N-methyl-D-aspartate receptor antagonist

OBJECT

The aims of this study were to clarify the histological and histochemical changes associated with cell death in the spinal cord after acute traumatic injury and to examine the role of excitatory amino acid release mediated by N-methyl-D-aspartate (NMDA) receptors.

METHODS

Following laminectomy, the spinal cord in 70 rats was injured at the T-9 level by applying extradural static weight-compression, in which a cylindrical compressor was used to induce complete and irreversible transverse spinal cord injury (SCI) with paralysis of the lower extremities. The injured rats were killed between 30 minutes and 14 days after injury, and the injured cord was removed en bloc. Rats that received NMDA receptor antagonist (MK-801) were killed at the same time points as those that received saline. The specimens were stained with hematoxylin and eosin, Nissl, and Klüver-Barrera Luxol fast blue and subjected to in situ nick-end labeling, a specific in situ method used to allow visualization of apoptosis. Thirty minutes post-SCI, a large hematoma was observed at the compressed segment. Six hours after injury, large numbers of dead cells that were not stained by in situ nick-end labeling were observed. Between 12 hours and 14 days postinjury, nuclei stained by using the in situ nick-end labeling technique were observed not only at the injury site but also in adjoining segments that had not undergone mechanical compression, suggesting that the delayed cell death was due to apoptosis. The number of cells stained by in situ nick-end labeling was maximum at 3 days postinjury. The results of electron microscopic examination were also consistent with apoptosis. In the MK-801-treated rats, the number of cells stained by in situ nick-end labeling was smaller than in nontreated rats at both 24 hours and 7 days after injury.

CONCLUSIONS

These findings suggest that NMDA-receptor activation promotes delayed neuronal and glial cell death due to apoptosis.

The hydroxyl radical scavenger Nicaraven inhibits glutamate release after spinal injury in rats

Neuronal degeneration after trauma is mediated in part by release of excitatory amino acids (EAAs) and oxygen free radicals (OFR). We evaluated the effect of i.v. treatment with a hydroxyl radical scavenger ((+/-)-N,N'-propylenedinicotinamide; AVS) and spinal hypothermia (33 degrees C) on spinal CSF glutamate release after spinal trauma. In a control group, spinal compression evoked at 10 min a significant increase (5-fold) in glutamate which declined over 4 h (2.1-fold). AVS treatment attenuated glutamate release but had no additive effect. These data suggest that this compound can be effective in modulating spinal excitotoxicity resulting from increased OFR synthesis and corresponding potentiation of EAA release.

Na+ channel block prevents the ischemia-induced release of norepinephrine from spinal cord slices

The principal finding of the present study with rat spinal cord slices was the novel demonstration of the [Ca2+]o-independent effect of ischemia on norepinephrine release and its antagonism by tetrodotoxin and low temperature (10 degrees C). Our finding that tetrodotoxin antagonized the effects of glucose deprivation on norepinephrine release in a [Ca2+]o-independent way suggests that Na+ channel block alone, i.e., the prevention of Na+ accumulation, may account for the protective action. Low temperature completely prevented the effect of ischemia on norepinephrine release but did not change the release associated with axonal activity. This finding is in good agreement with the observation that small changes in brain temperature critically determine the extent of neuronal injury from ischemia and suggests that both [Ca2+]o-independent release and cell injury are associated with the norepinephrine membrane carrier. It is suggested, therefore, that drugs able to attenuate the increase in [Na+]i during ischemia may be useful agents to protect against ischemic damage if given before the insult.

Changes of amino acid levels and aspartate distribution in the cervical spinal cord after traumatic spinal cord injury

To evaluate the role of excitatory amino acids in secondary injury occurring after spinal cord trauma, several experimental studies focusing on the the changes of amino acid levels in the spinal cord have been performed to date. However, because of technical limitations, it has not been possible to correlate the local changes of excitatory amino acids with the total tissue levels of excitatory amino acids. To investigate the connection between the spread of injury and the excitatory amino acids, we assessed, the local changes of aspartate through novel experimental approaches like immunoreactivity via fluorescence microphotometry and histopathology while also analyzing the total tissue levels of amino acids via HPLC. These studies were performed using a model of incomplete cervical spinal cord injury in rats. Through this approach, we found that the levels of excitatory amino acids, such as glutamate and aspartate, began to decrease immediately after injury. No significant decrease was observed in the other amino acids. Similarly, local changes in aspartate in the spinal cord were observed using fluorescence microphotometry. The decrease in the anterior and posterior horns was rapid up to 15 min after injury, but, slowed thereafter, suggesting that a release of excitatory amino acids occurred at the site of primary injury almost immediately following injury. At 15-min post-injury large neurons within the injured cord appeared intact on histopathological analysis demonstrating that the alteration of excitatory amino acids occurs prior to histopathological change. Histopathological change in the white matter occurred more slowly than in the anterior and posterior horns, suggesting the spread of the lesion by secondary damage due to an autoclastic mechanism.

Spinal effects of bicuculline: modulation of an allodynia-like state by an A1-receptor agonist, morphine, and an NMDA-receptor antagonist

Single-unit recordings were made in the intact anesthetized rat of the responses of dorsal horn neurons to C-, Adelta-, and Abeta-fiber stimulation. The postdischarge and windup responses of the same cells along with responses to innocuous stimuli, prod and brush, also were measured. The effects of (-)-bicuculline-methobromide (0.5, 5, 50, and 250 microg) were observed on these neuronal responses. The C- and Adelta-fiber-evoked responses were facilitated significantly in a dose-dependent manner. The input was facilitated, but as the final overall response was not increased by the same factor, windup appeared to be reduced. However, postdischarge, resulting from the increase in the excitability produced by windup, tended to be facilitated. After doses of >/=5 microg bicuculline, stimulation at suprathreshold Abeta-fiber-evoked activity caused enhanced firing, mainly at later latencies corresponding to Adelta-fiber-evoked activity in normal animals. Few cells responded consistently to brush and so no significant change was observed. Responses evoked by innocuous pressure (prod) always were observed in cells that concurrently responded to electrical stimulation with a C-fiber response. This tactile response was facilitated significantly by bicuculline. The effects of N6-cyclopentyladenosine (N6-CPA), an adenosine A1-receptor agonist, was observed after pretreatment with 50 microg bicuculline, as were the effects of morphine and 7-chlorokynurenate (7-CK). N6-CPA inhibited prod, C- and Adelta-fiber-evoked responses as well as the initial and overall final response to the train of C-fiber strength stimuli. Inhibitions were reversed with 8(p-sulphophenyl) theophylline. Morphine, the mu-receptor agonist, also inhibited the postbicuculline responses to prod, C-, and Adelta-fiber responses and initial and final responses to a train of stimuli. Inhibitory effects of morphine were reversed partly by naloxone. 7-CK, an antagonist at the glycine site on the N-methyl-D-aspartate-receptor complex, inhibited the responses to C- and Adelta-fiber-evoked activity as well as prod. The postdischarges were inhibited by this drug. Again both the initial and overall responses of the cell were inhibited. To conclude, bicuculline caused an increase in the responses of deep dorsal horn cells to prod, Adelta-fiber-evoked activity, increased C-fiber input onto these cells along with the appearance of responses at latencies normally associated with Adelta fibers, but evoked by suprathreshold Abeta-fiber stimulation. These alterations may be responsible for some aspects of the clinical phenomenon of allodynia and hyperalgesia. These altered and enhanced responses were modulated by the three separate classes of drugs, the order of effectiveness being 7-CK, N6-CPA, and then morphine.

Injury zone denervation in traumatic quadriplegia in humans

In order to obtain an electrophysiological characterization of the injury zone in traumatic quadriplegia, we performed electromyography and nerve conduction studies on the upper limbs of 15 patients with cervical cord trauma. Evidence of significant axonal loss was found in multiple myotomes of all patients. In most cases, the level of the most severe denervation, as determined by the absence or diminution of the compound motor action potential and the density of fibrillation potentials, was 2-5 spinal segments below the clinically and radiologically defined injury levels. In patients with injuries, the rostral extent of which is at C5 or higher, the most obvious clinical and electromyographic denervation was seen in the intrinsic hand muscles (C8/T1), with complete loss of C8/T1 motor axons in a subset of these patients. Our results document that spinal cord trauma can cause loss of motor axons in regions several segments caudal to the rostral level of injury. This finding may have implications for the pathophysiology of secondary injury, for recovery potential, and for the design of rehabilitation strategies.

Efficacy of high dose amino acid solution on spinal cord injury induced by focal Nd:YAG laser irradiation

In this experimental study, a neodymium:yttrium-aluminium-garnet (Nd:YAG) laser was used to induce highly reproducible focal spinal cord lesions in anaesthetized guinea pigs. The efficacy of high dose amino acid solution (HDAAS) on this injury is investigated. Experiments were performed on 36 animals divided into three groups; sham operated controls, laser irradiated surgical controls, and amino acid groups. Acute responses to injury were evaluated with somatosensory (SSEP) and motor evoked potentials (MEP) and functional recovery was assessed for 8 weeks using the inclined plane technique. In the laser irradiated surgical control group, MEP disappeared one hour after the laser injury, but SSEP revealed changes of amplitude and latency. In this group, the average value of the inclined plane at 24 hours after the laser application was 45.3 +/- 1.4 degrees. In the amino acid group, at the sixth hour of injury, MEP and SSEP changes improved with infusion of HDAAS for 4 hours. This improvement was statistically significant (for latency of SSEP U = 140 p < 0.05). Inclined plane value at 24 hours after the laser application was 65.5 +/- 1.2 degrees in this group. This study showed that application of Nd:YAG laser irradiation on the spinal cord induced spinal cord injury which presented as paraparesis, HDAAS may provide significant therapeutic protection in secondary damage following this injury and may have a potential role in the treatment of acute spinal cord injury.

An experimental model combining microdialysis with electrophysiology, histology, and neurochemistry for studying excitotoxicity in spinal cord injury. Effect of NMDA and kainate

We used an experimental model that we previously developed to characterize the damage caused by the agonists of glutamate receptors, N-methyl-D-aspartate (NMDA) and kainate, in the spinal cord in vivo, thereby testing further the utility of this model. Microdialysis was used to administer the toxins and to sample the release of other substances in response to these agents. The blockage of electrical conduction was monitored by recording the amplitudes of evoked potentials during administration of the damaging substances, and damage was assessed by postmortem histological examination. The released amino acids in microdialysates were measured by HPLC. Administration of 5 mM NMDA + 5 mM kainate into the gray matter blocked most postsynaptic responses and caused the release of amino acids. Administration of 10 mM NMDA and 10 mM kainate significantly destroyed cell bodies near the fiber. The advantage of this model is that histological, neurochemical, and electrophysiological parameters were obtained in the same experiment.

Traumatic optic neuropathy

Knowledge concerning the pathophysiologic mechanisms of traumatic optic neuropathy is limited. The optic nerve is a tract of the brain. Therefore, the cellular and biochemical pathophysiology of brain and spinal cord trauma and ischemia provide insight into mechanisms that may operate in traumatic optic neuropathy. The dosage of methylprednisolone (30 mg/kg/6 hours) which was successful in the National Acute Spinal Cord Injury Study 2 (NASCIS 2) evolved from the unique pharmacology of corticosteroids as antioxidants. The management of traumatic optic neuropathy rests on an accurate diagnosis which begins with a comprehensive clinical assessment and appropriate neuroimaging. The results of medical and surgical strategies for treating this injury have not been demonstrated to be better than those achieved without treatment. The spinal cord is a mixed grey and white matter tract of the brain in contrast to the optic nerve which is a pure white matter tract. The treatment success seen with methylprednisolone in the NASCIS 2 study may not generalize to the treatment of traumatic optic neuropathy. Conversely, if the treatment does generalize to the optic nerve, NASCIS 2 data suggests that treatment must be started within eight hours of injury, making traumatic optic neuropathy one of the true ophthalmic emergencies. Given the uncertainties in the treatment, ophthalmologists involved in the management of traumatic optic neuropathy are encouraged to participate in the collaborative study of traumatic optic neuropathy.

Mechanisms of hypoxic and ischemic injury. Use of cell culture models

Cell cultures are useful tools to study the mechanisms involved in cell death following hypoxia or ischemia. By manipulating the extracellular environment, conditions that closely mimic the conditions that are thought to occur in vivo can be produced. These conditions permit study of cell's reaction to the trauma under specific conditions. Monitoring of the extracellular pH and ionic environment in cell cultures is much easier than in vivo. Further, metabolites produced by injured cells can be quantitated easier from cultures than from tissues in vivo. Cell cultures have recently been used to examine in detail the neurotoxicity of glutamate. Intracellular Ca2+ increases appear to be involved in the mechanisms of neurotoxic cell death. This Ca2+ entry appears to be through the NMDA receptor's Ca2+ channel. Ischemic and hypoxic injury produced by mechanisms other than glutamate neurotoxicity appear to involve increases in intracellular Ca2+ by releasing internal Ca2+ stores or by the influx of extracellular Ca2+. This Ca2+ entry may be through voltage-gated channels of the NMDA channel, or may be attributable to membrane perturbations. Through the use of cell cultures, each of the mechanism's involvement in the injury can be delineated.

Protective effect of the NMDA antagonist MK-801 on photochemically induced spinal lesions in the rat

Photochemically induced ischemic lesions in the rat spinal cord were studied using neurological tests and morphological evaluation in order to investigate ischemia-mediated pathophysiological mechanisms in traumatic spinal cord injury. One week after ischemic lesioning, animals were severely impaired with 85% decrease of performance in neurological tests. During the next 2 weeks considerable recovery occurred. Pretreatment with the noncompetitive N-methyl-D-aspartate antagonist MK-801 at a dose of 0.5-1.0 mg/kg significantly improved the recovery of function after spinal ischemia while lower doses exerted no protection. Morphologically, no dose-response effect on the extent of tissue necrosis was found, but a significant difference between groups with severe neurological deficit versus mildly affected groups was observed. Immunohistochemical staining for glial fibrillary acidic protein in the area close to the lesion revealed extensive gliosis, while neurofilament immunohistochemistry showed an irregular pattern of fiber loss with large variability between animals. The degree of gliosis or loss of neurofilament immunoreactivity in nonnecrotic tissue was not affected by MK-801. These results suggest that excessive stimulation of N-methyl-D-aspartate receptors participates in the development of spinal cord ischemia and possibly also participates after traumatic spinal cord injury.