Thienylphencyclidine protection for the spinal cord of adult rats against extension of lesions secondary to a photochemical injury

A remotely controlled model of spinal cord compression injury in mice: toward real-time analysis

OBJECT

To date, there has been no efficient therapeutic approach to spinal cord injuries (SCIs). This may be attributable, at least in part, to difficulties in forming predictive and accurate experimental animal models. The authors' previous studies have identified 2 relevant conditions of such a model. The first condition is the ability to compare data derived from rat models of SCI by developing mouse models of SCI that permit access to a large range of transgenic models. The second condition is that the exploration of the consequences of each mechanism of spinal trauma requires modeling the different etiologic aspects of the injury.

METHODS

To fulfill these 2 conditions a new model of mouse spinal cord compression injury was devised using a thread-driven olive-shaped compressive device. The authors characterized early motor, sensory, and histological outcomes using 3 olive diameters and different compression durations.

RESULTS

A gradual and reproducible functional severity that correlated with lesion extension was demonstrated in 76 mice. To further substantiate the characterization of this model, a noncompetitive N-methyl-d-aspartate antagonist was administered in 30 mice, which demonstrated the involvement of excitotoxicity in this model.

CONCLUSIONS

The study demonstrated that spinal olive-compression injury in the mouse is a reproducible, well-characterized, and predictable model for analyzing early events after SCI. The nonmagnetic and remotely controlled design of this model will allow completion of the lesion while the animal is in the MR imaging apparatus, thus permitting further real-time MR imaging studies that will provide insights into the characterization of early events in the spatial and temporal evolution of SCI. Moreover, this model lays the foundation for future in vivo studies of functional and histological outcomes following SCI in genetically engineered animals.

Delayed intervention with transplants and neurotrophic factors supports recovery of forelimb function after cervical spinal cord injury in adult rats

The adult central nervous system is capable of considerable anatomical reorganization and functional recovery after injury. Functional outcomes, however, vary greatly, depending upon size and location of injury, type and timing of intervention, and type of recovery and plasticity evaluated. The present study was undertaken to assess the recovery of skilled and unskilled forelimb function in adult rats after a C5/C6 spinal cord over-hemisection and delayed intervention with fetal spinal cord transplants and neurotrophins. Recovery of forelimb function was evaluated during both target reaching (a skilled behavior) and vertical exploration (an unskilled behavior). Anatomical tracing and immunohistochemistry were used to assess the growth of descending raphespinal, corticospinal, and rubrospinal fibers at the injury site, tracts that normally confer forelimb function. Delayed intervention with transplants and either brain-derived neurotrophic factor (BDNF) or neurotrophin-3 (NT-3) restored skilled left forelimb reaching to pre-injury levels. Animals showed recovery of normal reaching movements rather than compensation with abnormal movements. Transplants and NT-3 also improved right forelimb use during an unskilled vertical exploration, but not skilled right reaching. Intervention with fetal transplant tissue supported the growth of descending serotonergic, corticospinal, and rubrospinal fibers into the transplant at the lesion site. The addition of neurotrophins, however, did not significantly increase axonal growth at the lesion site. These studies suggest that the recovery of skilled and unskilled forelimb use is possible after a large cervical spinal cord injury following delayed intervention with fetal spinal cord and neurotrophins. Plasticity of both spared and axotomized descending pathways likely contributes to the functional recovery observed.

Intrathecal bupivacaine protects against extension of lesions in an acute contusive spinal cord injury model

BACKGROUND AND OBJECTIVE

We recently demonstrated that intrathecal bupivacaine before or after acute photochemical spinal injury improved functional outcome in rats. However, the closest model to spinal trauma is the contusive weight-drop method. The aim of this study was to evaluate functional, electrophysiological and anatomical consequences of a contusive spinal-cord lesion in rats with or without an intrathecal injection of bupivacaine.

METHODS

Fifteen minutes before a contusive spinal lesion, 18 rats received intrathecally either 0.5% bupivacaine (Group T) or saline (Group C). During an 18-days period, motor and sensory functions were evaluated, and bladder voiding dysfunction was noted. Somatosensory evoked potential testings were performed at day 18. Then, the intact spinal cord area at the epicentre of the lesion and the extent of the lesion were measured.

RESULTS

Motor deficit was less and inclined-plane stability was better in treated animals at all times, the scores were statistically different from day 7. There were no differences concerning the sensory test. Despite no significant difference, there were less spinal bladders in the T group from day 7. Somatosensory evoked potential latencies were longer in T group, but only the first negative component (N1) was statistically significant. Amplitudes were higher in T group, but were not statistically different. The spinal cord intact area at the epicentre of the lesion was higher in the T group (1.23 +/- 0.8 mm(2) vs. 0.81 +/- 0.39 mm(2); P < 0.05). The extent of the lesion was higher in the C group (9.4 +/- 2.9 mm vs. 6.4 +/- 3.4 mm; P < 0.05).

CONCLUSION

Intrathecal 0.5% bupivacaine provide a neuroprotective effect by decreasing functional, electrophysiological and anatomical consequences after a contusive spinal cord injury.

Effects of citicoline on experimental spinal cord injury

OBJECTIVE

To investigate the effects of citicoline on experimental spinal cord injury (SCI).

BACKGROUND

Citicoline has been successfully used in clinical studies of head injury and cerebral infarction, but there is limited literature regarding its use in experimental SCI.

STUDY DESIGN

Twenty adult Wistar rats were divided into four groups: sham, trauma, vehicle, and citicoline-treated. SCI was produced using a weight drop technique. Citicoline 300 mg/kg was given intraperitoneally, 5 minutes after the induction of trauma. The animals were sacrificed and 1 cm long samples of injured spinal cord were obtained at 48 hours post-SCI. Lipid peroxidation was estimated by the thiobarbituric acid test. Neurological examinations were performed using a previously described grading scale.

RESULTS

Measures of lipid peroxidation and motor scores of the citicoline-treated group were significantly lower than those in the other injury groups.

CONCLUSIONS

Citicoline attenuated lipid peroxidation after SCI and improved the motor scores. Further investigations will be required to determine the long-term effects of this drug on spinal cord injury.

Nuclear magnetic resonance microimaging of mouse spinal cord in vivo

The spinal cord is the site of traumatic injuries, the devastating consequences of which constitute a public health problem in our societies. So far, there is no efficient repair therapeutic approach, and this is mainly due to the great difficulty for elaborating predictive experimental models of this pathology. Up to now, most pathophysiological studies were based on postmortem evaluation of the quantity and extent of the lesions, and their comparison in-between human and rodent specimen. Recent progresses of magnetic resonance imaging provide new tools to examine in vivo rodent central nervous system, and eventually to monitor the progression of lesions. However, up to now, mice spinal cord has been inaccessible to such studies, due to specific physiological characteristics and to the small size of the cord. In this study, the first diffusion-weighted images depicting the mouse thoracic spinal cord in vivo are shown. Motion-related artifacts are significantly reduced by respiratory gating using a dedicated sensor. By changing the direction of diffusion-sensitizing gradients, different contrasts were obtained that are compared with ex vivo MRI and histological preparations. In addition, preliminary results obtained on pathological cords are presented.

Intrathecal bupivacaine protects against extension of lesions in an acute photochemical spinal cord injury model

PURPOSE

The photochemical spinal-cord injury model reproduces extensive secondary lesions that occur after spinal injury. We have evaluated in 27 rats the functional, electrophysiological and anatomical consequences of a photochemical spinal-cord lesion induced before or after intrathecal injection of bupivacaine.

METHODS

After randomization, nine rats received 20 micro L of intrathecal bupivacaine 0.5% 15 min before a photochemical spinal-cord lesion (Group I) and eight rats received 20 micro L intrathecal bupivacaine 15 min after such a lesion (Group II). Ten rats received 20 micro L of saline 15 min before the photochemical injury (control group). Paraplegia was tested on days one, three, five, seven, nine, 12, 15 and 18 using an evaluation of hindlimb movements and an inclined plane stability test. Sensory block was evaluated by the animal's response when each hindlimb was brought into contact with a hot plate. Sympathetic injury was evaluated in terms of bladder voiding dysfunction. On day 18, residual somatosensory evoked potentials (SEP) were measured and the area of the intact spinal cord was determined using a digitalized system.

RESULTS

Early paraplegia recovery was found in the two bupivacaine groups (P < 0.05). On day 12, motor recovery was complete in both bupivacaine groups whereas recovery was not complete on day 18 in the control group. Compared to the control group, inclined plane stability recovered earlier in Groups I and II, from day three to day 15. Sensory and sympathetic block scores were not different in the three groups. Nevertheless, SEP latencies were longer and amplitudes were lower in control group rats compared with the two bupivacaine groups on day 18. The intact spinal-cord cross-sectional area around the lesion was not different in the three groups.

CONCLUSION

Twenty microlitres of intrathecal bupivacaine before or after acute photochemical spinal injury improves hindlimb motor recovery and SEP parameters in rats.

Strategies for regeneration and repair in spinal cord traumatic injury

Spinal cord injury is frequently followed by the loss of supraspinal control of sensory, autonomic and motor functions at the sublesional level. In order to enhance recovery in spinal cord-injured patients, we have developed three fundamental strategies in experimental models. These strategies define in turn three chronological levels of postlesional intervention in the spinal cord. Neuroprotection soon after injury using pharmacological tools to reduce the progressive secondary injury processes that follow during the first week after the initial lesion. This strategy was conducted up to clinical trials, showing that a pharmacological therapy can reduce the permanent neurological deficit that usually follows an acute injury of the central nervous system (CNS). A second strategy, which is initiated not long after the lesion, aims at promoting axonal regeneration by acting on the main barrier to regeneration of lesioned axons: the glial scar. Finally a mid-term substitutive strategy is the management of the sublesional spinal cord by sensorimotor stimulation and/or supply of missing key afferents, such as monoaminergic systems. These three strategies are reviewed. Only a combination of these different approaches will be able to provide an optimal basis for potential therapeutic interventions directed to functional recovery after spinal cord injury.

Rho signaling pathway targeted to promote spinal cord repair

The Rho signaling pathway regulates the cytoskeleton and motility and plays an important role in neuronal growth inhibition. Here we demonstrate that inactivation of Rho or its downstream target Rho-associated kinase (ROK) stimulated neurite growth in primary cells of cortical neurons plated on myelin or chondroitin sulfate proteoglycan substrates. Furthermore, treatment either with C3 transferase (C3) to inactivate Rho or with Y27632 to inhibit ROK was sufficient to stimulate axon regeneration and recovery of hindlimb function after spinal cord injury (SCI) in adult mice. Injured mice were treated with a single injection of Rho or Rho-associated kinase inhibitors delivered in a protein adhesive at the lesion site. Treated animals showed long-distance regeneration of anterogradely labeled corticospinal axons and increased levels of GAP-43 mRNA in the motor cortex. Behaviorally, inactivation of Rho pathway induced rapid recovery of locomotion and progressive recuperation of forelimb-hindlimb coordination. These findings provide evidence that the Rho signaling pathway is a potential target for therapeutic interventions after spinal cord injury.

A mouse model of acute ischemic spinal cord injury

Mice models of spinal cord injury (SCI) should improve our knowledge of the mechanisms of injury and repair of the nervous tissue. They represent a powerful tool for the development of therapeutic strategies in the fields of pharmacological, cellular, and genetic approaches of neurotrauma. We demonstrate here that the photochemical graded ischemic spinal cord injury model, described in rats, can be successfully adapted in mice, in a reliable and reproducible manner. Following the intravenous injection of Rose Bengal, the translucent dorsal surface of the T9 vertebral laminae of C57BL/6 female mice was irradiated with a 560-nm wavelength-light (3-8 min depending on the experimental group). Animals were sacrificed at 1 day or 7 days after injury. Functional tests were performed daily for motor, sensory, autonomic, and reflex responses. Lesion histopathology was assessed for lesion length, percentage of residual white matter, and astrocytic reactivity. Experimental groups demonstrated a functional deficit, which was correlated to the increase of the irradiation time and, therefore, to the severity of the injury. Histopathological and immunocytochemical data were reliable morphological measurements characterizing the degree of injury, which were strongly correlated to the severity of the functional impairment. Despite differences in the mechanism of injury, the wound healing response described in other traumatic SCI mice models was confirmed (no cavitation and, conversely, the formation of a dense connective tissue matrix). In this context, the precise understanding of the mechanisms of healing response after SCI in mice and of neurochemical kinetics appear to be crucial in the development of therapeutic strategies of CNS repair. Thus, the possible use of an increasing collection of transgenic mice offers a new dimension for experimental research in this area. The ischemic photochemical model of SCI in mice represents a relevant model that can play a key role in this new era of neurotrauma research.

Gacyclidine: a new neuroprotective agent acting at the N-methyl-D-aspartate receptor

Gacyclidine is a new phencyclidine derivative with neuroprotective properties. Tritiated gacyclidine and its enantiomers bind to NMDA receptors with binding parameters similar to those of other non-competitive NMDA receptor antagonists. The (-)enantiomer, (-)GK11, exhibits an affinity (2.5 nM) similar to that of dizocilpine (MK-801), while the (+)enantiomer, (+)GK11, has a 10 times lower affinity. When its interaction with NMDA receptors is prevented, gacyclidine binds also to "non-NMDA" binding sites which are mainly located in the molecular layer of the cerebellum on the dendritic tree of Purkinje cells. These binding sites do not appear to be related to any known neurotransmitters. In primary cortical cultures, gacyclidine and its enantiomers, at 0.1 to 5.0 microM, prevent glutamate-induced neuronal death. In rats, in vivo neurotoxicity of gacyclidine is far low than that of MK-801. No necrotic neurons were detected in animals sacrificed at 18 or 96 h after treatment with gacyclidine (1, 5, 10 or 20 mg/kg i.v.). At the highest (20 mg/kg) but not the lower doses (1-100 mg/kg) electron microscopy revealed the presence of few cytoplasmic or intramitochondrial vacuoles. In soman-treated monkeys gacyclidine enhanced neuroprotective activity of "three drugs cocktail" (atropine + diazepam + pralidoxime). Moreover, in rats, gacyclidine exerts a dose- and time-dependent neuroprotection in three models of spinal cord lesion. Beneficial effects of gacyclidine include reduction of lesion size and improvement of functional parameters after injury. In traumatic brain injury models gacyclidine improves also behavioral parameters and neuronal survival. Optimal protection is obtained when gacyclidine is administered at 0 to 30 min after injury. It is, therefore, concluded that gacyclidine exhibits neuroprotective effects similar to those of other NMDA receptor antagonists, with the advantage of being substantially less neurotoxic maybe due to its interaction with "non-NMDA" binding sites.

Gacyclidine: a new neuroprotective agent acting at the N-methyl-D-aspartate receptor

Gacyclidine is a new phencyclidine derivative with neuroprotective properties. Tritiated gacyclidine and its enantiomers bind to NMDA receptors with binding parameters similar to those of other non-competitive NMDA receptor antagonists. The (-)enantiomer, (-)GK11, exhibits an affinity (2.5 nM) similar to that of dizocilpine (MK-801), while the (+)enantiomer, (+)GK11, has a 10 times lower affinity. When its interaction with NMDA receptors is prevented, gacyclidine binds also to "non-NMDA" binding sites which are mainly located in the molecular layer of the cerebellum on the dendritic tree of Purkinje cells. These binding sites do not appear to be related to any known neurotransmitters. In primary cortical cultures, gacyclidine and its enantiomers, at 0.1 to 5.0 microM, prevent glutamate-induced neuronal death. In rats, in vivo neurotoxicity of gacyclidine is far low than that of MK-801. No necrotic neurons were detected in animals sacrificed at 18 or 96 h after treatment with gacyclidine (1, 5, 10 or 20 mg/kg i.v.). At the highest (20 mg/kg) but not the lower doses (1-100 mg/kg) electron microscopy revealed the presence of few cytoplasmic or intramitochondrial vacuoles. In soman-treated monkeys gacyclidine enhanced neuroprotective activity of "three drugs cocktail" (atropine + diazepam + pralidoxime). Moreover, in rats, gacyclidine exerts a dose- and time-dependent neuroprotection in three models of spinal cord lesion. Beneficial effects of gacyclidine include reduction of lesion size and improvement of functional parameters after injury. In traumatic brain injury models gacyclidine improves also behavioral parameters and neuronal survival. Optimal protection is obtained when gacyclidine is administered at 0 to 30 min after injury. It is, therefore, concluded that gacyclidine exhibits neuroprotective effects similar to those of other NMDA receptor antagonists, with the advantage of being substantially less neurotoxic maybe due to its interaction with "non-NMDA" binding sites.

Efficacy of a new neuroprotective agent, gacyclidine, in a model of rat spinal cord injury

Prevention of the immediate excitotoxic phase occurring in response to spinal cord injury (SCI) is a major issue to reduce the neuronal damage responsible for any ensuing motor deficits. The present study evaluated the neuroprotective efficacy of three noncompetitive NMDA receptor antagonists: Gacyclidine (GK-11), a new compound, Dizocilpine (MK-801), and Cerestat (CNS-1102) in a rat spinal cord contusion model. To mimic human SCI, a standardized model of rat spinal cord closed contusion in which animals spontaneously and progressively recover from the induced paraplegia was employed. Such model, characterized by a slow recovery of hindlimb locomotor function enables easy quantification of the neuroprotection at both the behavioral and cellular level. The animals were treated intravenously with the respective drugs 10 min after the spinal contusion. The dose range study suggested that 1 mg/kg of Gacyclidine was the most effective dose to promote functional recovery in reducing by half the time needed to reach full locomotor recovery. Racemate and enantiomers of Gacyclidine showed similar neuroprotective effects, but treatment with the enantiomers were not as efficacious in promoting full functional recovery. Similarly, a prolonged treatment with the racemate was not as efficious as a single dose, suggesting that a prolonged blockade of the amino-excitatory neurotransmission may be deleterious. Finally, Dizocilpine and Cerestat treatments induced only a partial and delayed neuroprotective effect compared to Gacyclidine. Neuroprotection characterized by a reduction of the cystic cavity and of the astrogliosis was observed with all treatments. As Gacyclidine is already in clinical trials, the present findings suggest the premise that it is a promising agent for limiting the initial neuronal damage induced by CNS trauma leading to better functional recovery.

Neuroprotective effects of a novel NMDA antagonist, Gacyclidine, after experimental contusive spinal cord injury in adult rats

The aim of this study was to analyze the optimal time-window for neuroprotection by a novel NMDA antagonist, Gacyclidine, after experimental spinal cord injury, in terms of its functional, histopathological and electrophysiological effects. This molecule has already demonstrated its capacity for reducing the extent of an ischemic lesion and is currently experimented in a clinical trial of spinal cord injury. In this study, the spinal cord of rats was damaged by a contusive method and the animals were treated by saline or 1 mg/kg of Gacyclidine i.v., 10, 30, 60 and 120 min after injury. The time-course of the motor score was evaluated on days 1, 7 and 18 after injury, and somatosensory evoked potentials were determined on day 20. The animals were then killed and the cross-sectional area of the spinal cord (at the epicenter of the injury, above and below the injury), was measured. Walking recovery was better (P<0.0125) in the group treated 10 min after injury than in the untreated injured animals after 18 days of injury. Motor performances were related to the preservation of a larger undamaged area of spinal cord at the level of the injury (P<0.0125). Somatosensory evoked potential amplitudes were also higher in this group. These results confirm that Gacyclidine attenuates spinal cord damage after an experimental spinal cord lesion. Recovery was better within the group treated 10 min after injury compared with the other groups, which certainly confirms that the acute time-course of glutamate release requires rapid pharmacological intervention to achieve good results.

Activation of locomotion in adult chronic spinal rats is achieved by transplantation of embryonic raphe cells reinnervating a precise lumbar level

Traumatic lesions of the spinal cord yield a loss of supraspinal control of voluntary locomotor activity, although the spinal cord contains the necessary circuitry to generate the basic locomotor pattern. In spinal rats, this network, known as central pattern generator (CPG), was shown to be sensitive to serotonergic pharmacological stimulation. In previous works we have shown that embryonic raphe cells transplanted into the sublesional cord of adult rats can reinnervate specific targets, restore the lesion-induced increase in receptor densities of neurotransmitters, promote hindlimb weight support, and trigger a locomotor activity on a treadmill without any other pharmacological treatment or training. With the aim of discriminating whether the action of serotonin on CPG is associated to a specific level of the cord, we have transplanted embryonic raphe cells at two different levels of the sublesional cord (T9 and T11) and then performed analysis of the kinematic and EMG activity synchronously recorded during locomotion. Locomotor performances were correlated to the reinnervated level of the cord and compared to that of intact and transected nontransplanted animals. The movements expressed by T11 transplanted animals correspond to a well defined locomotor pattern comparable to that of the intact animals. On the contrary, T9 transplanted animals developed limited and disorganized movements as those of nontransplanted animals. The correlation of the locomotor performances with the level of reinnervation of the spinal cord suggests that serotonergic reinnervation of the L1-L2 level constitutes a key element in the genesis of this locomotor rhythmic activity. This is the first in vivo demonstration that transplanted embryonic raphe cells reinnervating a specific level of the cord activate a locomotor behavior.

Effects of spinal cord X-irradiation on the recovery of paraplegic rats

Axonal regrowth is limited in the adult CNS, especially in the spinal cord, one of the major sites of traumatic lesions. Pathophysiological changes occurring after spinal cord injury include complex acute, subacute, and late processes. In this study, we assessed whether X-irradiation interferes with the acute/subacute phases, thereby improving the functional recovery of paraplegic animals. Two days after acute compression of adult rat spinal cords, various doses (0, 2, 5, 10, 20 Gy) of X-rays were administered as one single dose to the compression site. The animals were functionally evaluated over the course of 1 month after injury, using the Tarlov scale and the Rivlin and Tator scale. We also designed a "physiological" scale, including an assessment of urinary function and infection, appropriate for the evaluation of spinal-cord-lesioned animals. Behavioral analysis suggested that the high doses, 20 Gy and, to a lesser extent, 5 and 10 Gy, were toxic, as shown by morbidity rate and "physiological" score. The 2-Gy group showed better motor performances than the lesioned nonirradiated (LNI) animals and the 5- and 20-Gy groups. Motor performance in the 5-, 10-, and 20-Gy groups was poorer than that seen in the LNI group. Gliosis was reduced in the 2-Gy group compared to LNI animals, and there was high levels of gliosis in the highly (>/=5 Gy) irradiated animals. There was a 23% less lesion-induced syringomyelia in the 2-Gy group than in the other groups (LNI and 5-20 Gy). Thus, low doses of X-rays may interfere with the formation of syringomyelia and glial scar, thereby facilitating the recovery of paraplegic animals. These findings suggest that low-dose irradiation of the lesion site, in association with other therapies, is a potentially promising treatment for improving recovery after spinal cord injury.

Neuroprotective effects of gacyclidine after experimental photochemical spinal cord lesion in adult rats: dose-window and time-window effects

The aim of this study was to evaluate the efficacy, optimal dose, and optimal time-window of gacyclidine, a novel N-methyl-D-aspartate (NMDA) receptor antagonist, in terms of its functional, histopathological, and electrophysiological effects after experimental spinal cord injury. The spinal cord of rats was damaged by a photochemical method and the animals were treated by saline or gacyclidine at doses of 1, 2.5, or 5 mg/kg 10 min after injury or gacyclidine 1 mg/kg 10, 30, 60, and 120 min after injury. The time-course of the motor score (walking and inclined-plane stability) was evaluated until day 18, and somatosensory evoked potentials were determined on day 18. The animals were then sacrificed, and the cross-sectional area of the spinal cord (at the epicenter of the injury, above and below the injury) was measured. Walking recovery was better in most of the groups treated after injury than in the untreated injured animals. Motor performances were related to preservation of a larger undamaged area of spinal cord at the level of the injury and, interestingly, with prevention of extension of the anatomical lesion above the level of the injury. Somatosensory evoked potential amplitudes were often higher in treated groups. These results confirm that gacyclidine induces dose-dependent and time-dependent attenuation of spinal cord damage after an experimental vascular lesion. Although all three doses induced neuroprotective effects, recovery was greater and very homogeneous in the group treated with 1 mg/kg. Moreover, recovery was slightly better and more homogeneous within the groups treated 10 and 30 min after injury compared to the other groups. It appears that, according to the existing evidence, NMDA antagonists are an essential component in the elaboration of a neuroprotective strategy after spinal cord trauma.

Chronic and acute compressive spinal cord lesions in dogs due to intervertebral disc herniation are associated with elevation in lumbar cerebrospinal fluid glutamate concentration

Acute injury to the central nervous system initiates a series of biochemical events that cause secondary tissue damage. The accumulation of excessive concentrations of glutamate in the extracellular space causes excitotoxic damage, and is incriminated as a mediator of this secondary tissue damage. The aim of this study was to measure the concentration of glutamate in cerebrospinal fluid (CSF) obtained from the cerebellomedullary cistern and lumbar subarachnoid space in dogs with acute and chronic compressive injuries of the cervical and thoracolumbar spinal cord, and to correlate the glutamate concentration with injury severity. The results demonstrate that focal injuries of the spinal cord do not affect the glutamate concentration in CSF taken from the cerebellomedullary cistern. However, dogs with severe, acute thoracolumbar disc herniations have two- to 10-fold increases in glutamate concentration in their lumbar CSF at intervals of >12 h after injury. Moreover, the severity of their clinical signs is directly related to the glutamate concentration. Dogs with chronic compressive thoracolumbar lesions have a two-fold elevation of CSF glutamate concentration, suggesting that excitotoxicity may also be a component of chronic spinal cord compression.

Recurrent glutamate stimulations potentiate the hydroxyl radicals response to glutamate

Neurotoxicity induced by hydroxyl radicals (OH) release is thought to be involved in a number of acute and chronical neuropathologies of the central nervous system. As far as neurodegenerative processes are concerned, the possible mechanisms giving rise to such OH releases remain poorly understood. In the present study, unanesthetized rats were perfused with a low salicylate solution through a chronic microdialysis cannula implanted into the striatum, and the OH responses to glutamate were analyzed. A single bolus of 3 mM glutamate elicited only minute releases of OH in naive rats. By contrast, recurrent infusions at 1-week intervals of the same glutamate concentration induced a robust OH response. Similar potentiation of the initial response also occurred for a larger glutamate concentration (30 mM). Oppositely, multiple injections of a high (300 mM) glutamate concentration resulted in a slow down of the initial OH response recorded in naive animals. The mechanisms giving rise to such effects are presently unknown. It is, however, clear that repetitive dysfunctions of the glutamate neurotransmission may be sufficient to promote the release of significant amounts of hydroxyl radicals, resulting in a progressive impairment of the astrocytic glutamate transporter, leading to neurodegenerative processes.

Biological interventions for spinal cord injury

Spinal cord injury is frequently followed by the loss of supraspinal control of sensory, autonomus and motor functions at sublesional level. To enhance recovery in patients with spinal cord injuries, three fundamental strategies have been developed in experimental models. These strategies involve three different time points for postlesional intervention in the spinal cord. Neuroprotection soon after injury uses pharmacological tools to reduce the progressive secondary injury processes that follow during the first week after the initial lesion occurs, in order to limit tissue damage. A second strategy, which is initiated shortly after the lesion occurs, aims at promoting axonal regeneration by acting pharmacologically on inhibitors or barriers of regeneration, or by the application of cell or gene therapy as a source of neurotrophic factors or as a bridge or support to enhance the regeneration of lesioned axons. Finally, a mid-term substitutive strategy is the management of the sublesional spinal cord by sensorimotor stimulation or the supply of missing key afferents, such as monoaminergic systems. These three strategies are reviewed. Only a combination of these different approaches can provide an optimal basis for potential therapeutic interventions aimed at functional recovery after spinal cord injury.

No protective effect of the NMDA antagonist memantine in experimental spinal cord injuries

We have investigated the effect of memantine, a clinically used NMDA receptor antagonist, in two experimental animals models of spinal cord injury. The lesions were laser-induced photothrombosis to induce focal spinal cord ischemia and clip compression to mimic traumatic spinal cord injury. Pre- or posttreatment of rats with a dose of memantine (20 mg/kg ip) previously shown to be neuroprotective in cerebral ischemia, failed to affect both the neurological and morphological outcome of ischemic spinal cord injury. Likewise, memantine had no effects on neurological and morphological outcome after experimental traumatic injury. In view of the regional heterogeneity of NMDA receptors, the affinity of memantine for spinal cord NMDA receptors was also determined by studying displacement of [3H] (+)-5-methyl-10,11-dihydro-5-H-dibenzo[a,d]cyclohepten-5-10-imine (MK-801) to rat and human spinal cord homogenates. We found that memantine had an affinity for NMDA receptors in the spinal cord (Ki = 0.58 microM) that was significantly lower compared to that of the cerebral cortex (Ki = 0.23 microM) and that the affinity for NMDA receptors in human spinal cord was even lower. We conclude that in view of available data, memantine should not be chosen for clinical studies on neuroprotection in spinal cord injuries and that the lack of protective effect is most likely due to insufficient affinity of memantine for spinal cord NMDA receptors.

Primary demyelination and regeneration of ascending axons in the dorsal funiculus of the rat spinal cord following photochemically induced injury

The extent of primary demyelination and regeneration of ascending axons in the dorsal funiculus of the rat spinal cord was investigated following photochemically-induced ischaemic injury. Groups of rats were killed at intervals from 48h to 1 month after injury and a combination of light and electron microscopy and counting of axons in specific sites was used to study the axonal changes. Unmyelinated axons were noted in the dorsal rim of the lesion at its centre and at the centre of the gracile fasciculus at the caudal end of the lesion 7 days after injury. By 1 month, axons in these sites were thinly myelinated by Schwann cells or oligodendrocytes. In order to differentiate between remyelination of demyelinated axons and myelination of regenerated axons, axon counts were performed. The number of sub-pial axons present at the lesion centre did not change significantly from 48h to 1 month after injury, whereas the number of axons at the caudal end of the lesion increased significantly from 4 to 10 days after injury. We therefore conclude that sub-pial axons at the lesion centre are demyelinated between 4 and 7 days after injury and subsequently remyelinated by Schwann cells. At the caudal end of the lesion, a specific population of small diameter axons located at the centre of the gracile fasciculus regenerates for a distance of approximately 1 mm between 4 and 10 days after injury; these axons are then myelinated by oligodendrocytes or Schwann cells. In contrast, larger diameter axons of the gracile fasciculus do not show a regenerative response, demonstrating the variability of axonal responses to injury.