Failure of tetracaine to reverse spinal cord injury in the cat

Spinal cord injury in the rat

Only limited therapeutic measures are currently available for the treatment of spinal cord injury. This review describes the pathologic mechanisms of trauma-induced spinal cord injury in rats, which will contribute to new understanding of the pathologic process leading to spinal cord injury and to further development of new therapeutic strategies. Spinal cord injury induced by trauma is a consequence of an initial physical insult and a subsequent progressive injury process that involves various pathochemical events leading to tissue destruction; the latter process should therefore be a target of pharmacological treatment. Recently, activated neutrophils have been shown to be implicated in the latter process of the spinal cord injury in rats. Activated neutrophils damage the endothelial cells by releasing inflammatory mediators such as neutrophil elastase and oxygen free radicals. Adhesion of activated neutrophils to the endothelial cell could also play a role in endothelial cell injury. This endothelial cell injury could in turn induce microcirculatory disturbances leading to spinal cord ischemia. We have found that some therapeutic agents that inhibit neutrophil activation alleviate the motor disturbances observed in the rat model of spinal cord injury. Methylprednisolone (MPS) and GM1 ganglioside, which are the only two pharmacological agents currently clinically available for treatment of acute spinal cord injury, do not inhibit neutrophil activation in this rat model. Taken together, these observations raise a possibility that other pharmacological agents that inhibit neutrophil activation used in conjunction with MPS or GM1 ganglioside may have a synergistic effect in the treatment of traumatic spinal cord injury in humans.

Protective effects of antiarrhythmic agents against anoxic injury in CNS white matter

Irreversible anoxic injury is dependent on extracellular Ca2+ in mammalian CNS white matter, with a large portion of the pathologic Ca2+ influx occurring through reverse Na(+)-Ca2+ exchange, stimulated by increased intracellular [Na+]. This Na+ leak likely occurs via incompletely inactivated voltage-gated Na+ channels. This study reports that clinically used antiarrhythmic compounds, likely by virtue of their Na+ channel-blocking properties, significantly protect CNS white matter from anoxia at concentrations that cause little suppression of the preanoxic response. Rat optic nerves were pretreated with various agents for 60 min, then subjected to 60 min of anoxia in vitro. Functional recovery was measured electrophysiologically as the area under the compound action potential (CAP). Without drug, the CAP areas recovered to a mean of 32 +/- 12% of control after 1 h of reoxygenation. Recoveries using prajmaline 10 microM were 82 +/- 15% (p < 0.0001), and using tocainide 1 mM, 78 +/- 8% (p < 0.0001), with little suppression (< or = 10%) of the preanoxic response. Ajmaline (10-100 microM), disopyramide (10-300 microM) and bupivacaine (10-100 microM) were somewhat less effective, whereas verapamil produced 52 +/- 11% recovery before reduction of the preanoxic CAP was observed at 30 microM. Procainamide (100-300 microM) was ineffective. These results suggest that Na+ channel blockers, including commonly used antiarrhythmic agents, may be effective in protecting central white matter, which is a target for anoxic/ischemic injury in diseases such as stroke and spinal cord injury.

Gallium nitrate and spinal cord injury. A pilot study of efficacy using an experimental model

Gallium (Ga) nitrate has been shown to attenuate immune-mediated tissue destruction in models of neurological autoimmunity. Based upon these observations, we evaluated the efficacy of Ga nitrate in attenuating the inflammatory response and modifying clinical recovery in an experimental model of traumatic spinal cord injury (SCI). Using a randomized, double-blind, placebo-controlled design, 12 adult female Sprague-Dawley rats received injections of either Ga nitrate (n = 8) or saline (n = 4) following experimental SCI. Ga treated animals received 30 mg/kg elemental Ga followed by weekly injections of 10 mg/kg elemental Ga. There were no observable differences between the Ga treated and the saline control groups using various behavioral paradigms examined during the study period. Histological and immunocytochemical data qualitatively showed no observable differences between Ga treated (n = 4) and control (n = 2) groups sacrificed 18 days following SCI. Although the efficacy of Ga in this pilot study of experimental SCI was not demonstrated, the potential of Ga to attenuate inflammatory-mediated reactions remains an exciting possibility in the area of SCI. Our preliminary results should not discourage future research endeavors in this regard. A more complete analysis of dose response, time and mode of Ga administration (preinjury or postinjury), and availability of Ga across the blood-brain barrier is needed to further evaluate the efficacy of this compound.

Failure of nimodipine to reverse acute experimental spinal cord injury

The calcium-channel blocking agent, nimodipine, was administered to cats for 5 days after acute experimental SCI. Six weeks after injury, no significant differences in neurologic recovery or white matter tissue preservation at the injury site were found between treated and control animals.