Effect of Anticonvulsant Felbamate on GABAA Receptor System

Felbamate (FBM, 2-phenyl-1,3-propanediol dicarbamate), a potential antiepileptic drug (AED), has an unknown mechanism of action. We examined possible interaction of FBM with GABAA ergic transmission. FBM did not alter specific binding of ligands to GABA. benzodiazepine, and picrotoxin sites of the oligomeric GABAA receptor complex to rat brain membranes, nor did it enhance the effect of GABA on 36Cl-influx in well-characterized cultured spinal cord neurons. These results suggest that the anticonvulsant effect of FBM does not involve GABAA ergic transmission.     

Anticonvulsant action of a non-competitive antagonist of NMDA receptors (MK-801) in the kindling model of epilepsy

Anticonvulsant action of MK-801, a novel non-competitive antagonist of N-methyl-d-aspartate (NMDA) receptors, was investigated in the kindling model of epilepsy in rats. The results obtained were as follows. (1) Both the seizure stage and afterdischarge duration of previously kindled seizures from the amygdala were significantly suppressed following systemic injection of MK-801 (0.25–4 mg/kg) in a dose-dependent manner. The maximum effects were observed between 2 and 4 h after the injection. (2) The MK-801 also showed significant anticonvulsant effedts on kindled seizures from the frontal cortex and the ventral and dorsal hippocampus. The efficacy however, significantly differed between these kindled sites. (3) Daily treatment of MK-801 (0.25 and 1 mg/kg) prior to each electrical stimulation of the amygdala significantly retarded kindling seizure development and increased the total amount of afterdischarge (accumulated AD) required to reach the first stage 5 seizure. During drug sessions of 1 mg/kg MK-801 for 19 days, all rats showed only partial seizures and the growth of afterdischarge was strongly prevented. (4) Pretreatment with reserpine did not antagonize the anticonvulsant effects of MK-801 on previously kindled seizures from the amydala, suggesting that the effects may not be mediated by catecholaminergic systems. These results indicate that MK-801 has potent anticonvulsant actions on kindled seizures from both limbic and cortical foci, the NMDA system may play a critical role in the seizure-triggering mechanism of kindling. The possible application of NMDA antagonists in clinical epilepsy is suggested.     

NMDA受体激活诱导甲醛炎性痛大鼠脊髓HO-1蛋白表达增加

目的本实验通过在甲醛炎性痛大鼠鞘内注射N-甲基-D-d门冬氨酸(NMDA)受体抑制剂地卓西平马来酸盐(MK-801)以及在正常大鼠鞘内注射NMDA受体激动剂NMDA,观察二者对甲醛炎性痛大鼠以及正常大鼠脊髓血红素氧合酶-1(HO-1)表达的影响,探讨甲醛炎性痛诱导的大鼠脊髓HO-1蛋白表达改变是否受NMDA受体激活的影响。方法采用右后掌足底注射甲醛复制炎性痛模型,采用免疫组织化学方法观察脊髓HO-1蛋白表达。结果甲醛炎性痛大鼠L5脊髓后角Ⅰ-Ⅱ板层HO-1蛋白免疫反应阳性细胞数目、平均光密度值均明显大于正常对照组,预先鞘内注射MK-801可明显抑制甲醛炎性痛诱导的大鼠双侧脊髓后角Ⅰ-Ⅱ板层HO-1蛋白的表达,正常大鼠鞘内注射NMDA可诱导脊髓后角HO-1蛋白表达增加。结论 NMDA受体激活可促进脊髓神经元HO-1蛋白的表达。     

A polysialic acid mimetic peptide promotes functional recovery in a mouse model of spinal cord injury

Contrary to lower species that recapitulate some of the developmental programs, in mammals, functional recovery after spinal cord injury is impaired by a non-permissive environment and the lack of plasticity of adult neurons. The developmental plasticity associated linear homopolymer of alpha 2,8-linked sialic acid (PolySialic Acid, PSA), represents a permissive determinant that could contribute to recovery. We previously showed that a PSA cyclic mimetic peptide (PR-21) displayed PSA-like biological functions (Torregrossa, P., Buhl, L., Bancila, M., Durbec, P., Schafer, C., Schachner, M., Rougon, G., 2004. Selection of poly-alpha 2,8-sialic acid mimotopes from a random phage peptide library and analysis of their bioactivity. J. Biol. Chem. 279, 30707–30714.). In the present study we investigated the therapeutic potential of PR-21 in young adult mice after dorsal hemisection at the T9 level. We show that PR-21 fulfills several criteria for an in vivo use as it is not toxic, not immunogenic and displays good stability in biological fluids or tissue. Delivery of PR-21 to the lesion site decreased the time of the animals' return to continence, and enhanced motor functions, sensorimotor control and coordination of hindlimbs with forelimbs when compared to a control peptide. At the cellular level, PR-21 increased serotonergic axon density at and caudal to the lesion site, and decreased reactive gliosis in vivo. In an in vitro model of reactive astrocytes, PR-21 increased NCAM expression in strongly GFAP positive cells. Our data point to the unique features of a carbohydrate mimicking peptide, and support the notion that PSA can be considered as an important factor in recovery from spinal cord injury.     

A re-assessment of erythropoietin as a neuroprotective agent following rat spinal cord compression or contusion injury

This study was initiated due to an NIH “Facilities of Research — Spinal Cord Injury” contract to support independent replication of published studies that appear promising for eventual clinical testing. We repeated a study reporting the beneficial effects of recombinant human erythropoietin (rhEPO) treatment after spinal cord injury (SCI). Moderate thoracic SCI was produced by two methods: 1) compression due to placement of a modified aneurysm clip (20 g, 10 s) at the T3 spinal segment (n=45) [followed by administration of rhEPO 1000 IU/kg/IP in 1 or 3 doses (treatment groups)] and 2) contusion by means of the MASCIS impactor (n = 42) at spinal T9 (height 12.5 cm, weight 10 g) [followed by the administration of rhEPO 5000 IU/kg/IP for 7d or single dose (treatment groups)]. The use of rhEPO following moderate compressive or contusive injury of the thoracic spinal cord did not improve the locomotor behavior (BBB rating scale). Also, secondary changes (i.e. necrotic changes followed by cavitation) were not significantly improved with rhEPO therapy. With these results, although we cannot conclude that there will be no beneficial effect in different SCI models, we caution researchers that the use of rhEPO requires further investigation before implementing clinical trials.     

Effect of post-injury NMDA antagonist treatment on long-term Fos expression and hyperalgesia in a model of chronic neuropathic pain

Chronic constriction injury (CCI) of the sciatic nerve results in persistent mechanical hyperalgesia together with Fos protein expression in the lumbar spinal cord. We have examined the relationship between mechanical hyperalgesia and Fos expression within the lumbar spinal cord on days 14, 35 and 55 after either CCI or sham operation. To determine the role of NMDA receptor mechanisms in the maintenance of hyperalgesia and Fos expression, the NMDA antagonist MK-801 (0.3 mg kg-1 s.c.) was administered daily on days 28 to 34 after operation. CCI animals developed unilateral hind limb hyperalgesia that persisted unchanged from days 14 to 55 of the study. MK-801 treatment reduced hyperalgesia by 57% (p=0.02) on day 35 in CCI animals but did influence hyperalgesia at day 55. In the spinal cord, Fos positive cells were present bilaterally throughout laminae 3-10 at all time points examined in both CCI and sham group animals. Fos counts ipsilateral to the side of injury in laminae 3-10 correlated significantly with hyperalgesia scores in the CCI but not sham animals. MK-801 treatment resulted in a suppression of Fos expression in ipsilateral laminae 3-4 (p=0.0017) and laminae 5-10 (p=0.0026) of CCI animals on day 35. Fos expression in sham group animals was not inhibited by MK-801 treatment at day 35. These results indicate that Fos expression is maintained by differing mechanisms following nerve injury or sham operation. The functional consequences of Fos expression following nerve injury and sham operation are discussed.     

Evaluation of the glutamate antagonist dizocilipine maleate (MK-801) on neurologic outcome in a canine model of complete cerebral ischemia: correlation with hippocampal histopathology

This study was designed to determine if dizocilipine maleate (MK-801), administered following 11 min of complete ischemia in dogs, could favorably alter neurologic outcome and hippocampal damage. Eighteen dogs were anesthetized and subjected to complete cerebral ischemia by temporary occlusion of the ascending aorta and the venae cavae via a thoracotomy. Five min postischemia, 9 dogs were given dizocilipine 150 micrograms/kg, followed by an infusion of 1.25 microgram/kg/min for 8 h. Control dogs were given equal volumes of placebo. Dogs were evaluated neurologically at 24, 48, and 72 h; thereafter, the brains were perfused, fixed and harvested. There was no significant difference in outcome between dizocilipine- and placebo-treated dogs: 5 of 9 given dizocilipine were normal, 1 was mildly injured and 3 were severely injured or dead. In the control animals given placebo, 3 of 9 were normal, 2 were mildly injured and 4 were moderately to severely injured. Histopathologic examination was limited to the hippocampus. CA1 and CA2,3,4 pyramidal neurons were graded according to degree of injury on a 5-point scale. There were no differences in histopathologic grades between the two groups. However, in both groups combined there was a significant correlation between neurologic outcome grade and histopathologic grade. The only notable systemic effect of dizocilipine appeared to be prolonged sedation which extended beyond 24 h postischemia but was not evident at 48 h postischemia. The authors conclude that more outcome studies in more sensitive models are needed.     

Beta-band oscillations as a biomarker of gait recovery in spinal cord injury patients: A quantitative electroencephalography analysis

ObjectiveThe gait recovery in spinal cord injury (SCI) seems to be partially related to the reorganization of cerebral function; however, the neural mechanisms and the respective biomarkers are not well known. This study tested the hypothesis that enhanced beta-band oscillations may be a marker of compensatory neural plasticity during the recovery period in SCI. We tested this hypothesis at baseline in SCI subjects and also in response to cortical stimulation with transcranial direct current stimulation (tDCS) combined with robotic-assisted gait training (RAGT).MethodsIn this neurophysiological analysis of a randomized controlled trial, thirty-nine patients with incomplete SCI were included. They received 30 sessions of either active or sham anodal tDCS over the primary motor area for 20 min combined with RAGT. We analyzed the Electroencephalography (EEG) power spectrum and task-related power modulation of EEG oscillations, and their association with gait function indexed by Walk Index for Spinal Cord Injury (WISCI-II). Univariate and multivariate linear/logistic regression analyses were performed to identify the predictors of gait function and recovery.ResultsConsistent with our hypothesis, we found that in the sensorimotor area: (1) Anodal tDCS combined with RAGT can modulate high-beta EEG oscillations power and enhance gait recovery; (2) higher high-beta EEG oscillations power at baseline can predict baseline gait function; (3) high-beta EEG oscillations power at baseline can predict gait recovery – the higher power at baseline, the better gait recovery; (4) decreases in relative high-beta power and increases in beta power decrease during walking are associated with gait recovery.ConclusionsEnhanced EEG beta oscillations in the sensorimotor area in SCI subjects may be part of a compensatory mechanism to enhance local plasticity. Our results point to the direction that interventions enhancing local plasticity such as tDCS combined with robotic training also lead to an immediate increase in sensorimotor cortex activation, improvement in gait recovery, and subsequent decrease in high-beta power. These findings suggest that beta-band oscillations may be potential biomarkers of gait function and recovery in SCI.SignificanceThese findings are significant for rehabilitation in SCI patients, and as EEG is a portable, inexpensive, and easy-to-apply system, the clinical translation is feasible to follow better the recovery process and to help to individualize rehabilitation therapies of SCI patients.     

Rostral ventrolateral medulla: a source of the glutamatergic innervation of the sympathetic intermediolateral nucleus

To determine whether the sympathoexcitatory projection from the rostral ventrolateral medulla (RVL) to the sympathetic intermediolateral nucleus (IML) of the spinal cord might use glutamate as an excitatory transmitter, we performed a dual-label, transport and immunocytochemical ultrastructural study. Axon terminals within the IML were examined to determine whether anterogradely transported Phaseolus vulgaris-leucoagglutinin (PHA-L) following injections into the RVL, was colocalized with glutamate immunoreactivity using an antibody to hemocyanin-conjugated L-glutamate (Hepler et al., J. Histochem. Cytochem., 36 (1988) 13-22). Transported PHA-L was visualized with the peroxidase-antiperoxidase technique while glutamate-like immunoreactivity was localized within the same section of the thoracic spinal cord with immunoautoradiography. By light microscopy, PHA-L immunoreactivity was found within a plexus of fine fibers and varicose processes localized to the IML. Silver grains indicative of glutamate immunoreactivity were concentrated over the IML and also over the superficial layers of the dorsal horn. Electron microscopic analysis revealed PHA-L immunoreactivity in axons and axon terminals within the IML. They ranged in diameter from 0.5 to 2.0 microns, contained numerous small clear and 0-3 large, dense-core vesicles, and formed primarily asymmetric synaptic contacts on small dendrites of IML neurons. Some of the PHA-L immunoreactive terminals making asymmetric (excitatory) synaptic contacts on the small dendrites of IML neurons also contained glutamate-like immunoreactivity. We conclude that at least a portion of the input to the IML from the RVL uses glutamate as its transmitter.(ABSTRACT TRUNCATED AT 250 WORDS)     

The Dorsal Root Ganglion as a Novel Neuromodulatory Target to Evoke Strong and Reproducible Motor Responses in Chronic Motor Complete Spinal Cord Injury: A Case Series of Five Patients

ObjectivesCurrent strategies for motor recovery after spinal cord injury (SCI) aim to facilitate motor performance through modulation of afferent input to the spinal cord using epidural electrical stimulation (EES). The dorsal root ganglion (DRG) itself, the first relay station of these afferent inputs, has not yet been targeted for this purpose. The current study aimed to determine whether DRG stimulation can facilitate clinically relevant motor response in motor complete SCI.Materials and MethodsFive patients with chronic motor complete SCI were implanted with DRG leads placed bilaterally on level L4 during five days. Based on personalized stimulation protocols, we aimed to evoke dynamic (phase 1) and isotonic (phase 2) motor responses in the bilateral quadriceps muscles. On days 1 and 5, EMG-measurements (root mean square [RMS] values) and clinical muscle force measurements (MRC scoring) were used to measure motor responses and their reproducibility.ResultsIn all patients, DRG-stimulation evoked significant phase 1 and phase 2 motor responses with an MRC ≥4 for all upper leg muscles (rectus femoris, vastus lateralis, vastus medialis, and biceps femoris) (p < 0.05 and p < 0.01, respectively), leading to a knee extension movement strong enough to facilitate assisted weight bearing. No significant differences in RMS values were observed between days 1 and 5 of the study, indicating that motor responses were reproducible.ConclusionThe current paper provides first evidence that bilateral L4 DRG stimulation can evoke reproducible motor responses in the upper leg, sufficient for assisted weight bearing in patients with chronic motor complete SCI. As such, a new target for SCI treatment has surfaced, using existing stimulation devices, making the technique directly clinically accessible.