An electromechanical spinal injury technique with dynamic sensitivity.

Over the past decade, our laboratory has attempted to create a simple, accurate device that could be used to produce reliable and quantifiable spinal cord injuries in the rodent. We report here on our latest of several modifications of a spinal cord impactor that has allowed us to meet these design criteria. The impactor uses the dynamic capacity of an electromagnetic driver (Ling shaker) and a unique pattern generator to briefly compress the dorsal surface of the spinal cord at velocities that may mimic compression injuries seen in the human. Calibrated, independent transducer systems provide open-loop output of the precise movement (displacement) of the impactor probe and the force necessary to achieve a given displacement. Touch sensitivity is accomplished by vibrating the probe slightly as it approaches the dural surface. This also allows a known biomechanical starting point. This combination of improvements in sensitivity and ability to measure all components of the dynamic compression has allowed us to determine detailed biomechanical descriptors of these impact injuries with low coefficients of variation. Furthermore, such descriptors correlate highly with histopathologic and behavioral outcome measures in animal populations with a variety of injury severities.

Spinal cord injury produced by consistent mechanical displacement of the cord in rats: behavioral and histologic analysis.

We examined the ability of an electromechanical device to produce consistent and incomplete thoracic (T9) spinal cord injuries in rats by brief displacement (Dspl) of the exposed dural surface. Open field walking, inclined plane, grid walking, and footprint analysis, and a determination of the percentage of tissue spared at the lesion center were used to assess chronic outcome (6 weeks postinjury). Laminectomy control animals showed no evidence of a functional deficit or histologic lesion. Complete spinal cord transections in normal rats and in a group of animals previously injured (1.1 mm Dspl) and allowed to recover resulted in complete loss of hindlimb function, demonstrating an important functional role for the remaining spared fibers at the lesion site. Consistent spinal cord displacements (0.80 mm, 0.95 mm, and 1.10 mm) resulted in behavioral groups with low outcome variability over a narrow range of incomplete recovery of neurologic function. Significant behavioral (open field walking, inclined plane, and grid walking) and histologic differences were found between the control and Dspl groups and between the 0.80 mm and 1.10 mm Dspl groups. Significant correlations were observed among the injury parameters, behavioral, and histologic scores. Open field walking and inclined plane performance were sensitive indicators of both the early and late phases of neurologic recovery. Grid walking was most useful in animals with small chronic residual deficits. The footprint analysis resulted in less significant correlations and differences between the behavioral groups than the other outcome measures. This may result from a relatively narrow range of sensitivity (open field walking scores between 3.3 and 4.0) and increased variability within the groups.

Modeling of acute spinal cord injury in the rat: neuroprotection and enhanced recovery with methylprednisolone, U-74006F and YM-14673.

We used a new injury device that produces consistent spinal cord contusion injuries (T8) in rats to compare the behavioral and histologic effects of methylprednisolone sodium succinate (MPSS) administration, the clinical standard of therapy after acute spinal cord injury (ASCI), with the 21-aminosteroid, U-74006F (U74), and the TRH analogue, YM-14673 (YM), at different trauma doses. Three sequential experiments were conducted: Experiment 1. U74 (3.0/1.5/1.5 mg/kg; 10/5/5 mg/kg; 30/15/15 mg/kg), MPSS (30/15/15 mg/kg), or vehicle were administered intravenously (i.v.) at 5 min, 2 and 6 h after the injury (n = 8/group). U74 (10/5/5 mg/kg) and MPSS animals scored better than controls (Days 8-43) in open field walking (OFW); no other differences were seen between groups. Experiment 2. Dose-response evaluation of MPSS determined more effective doses. Groups (n = 16) receiving 30/30/30/30 mg/kg and 60/60/60/60 mg/kg i.v. at 5 min and 2, 4, and 6 h after the injury had better OFW scores than controls (Days 8-29; Day 29). Both groups performed better than controls (Days 8-29) on inclined plane (IP); 30 mg/kg animals scored higher on Day 29. Percentage tissue spared (%TS) at the lesion center was greater for 60 mg/kg animals (23.4%) than controls (17.3%). Experiment 3. Compounds were administered as in experiment 2 (n = 15/group); MPSS (60/30/30/30 mg/kg) and YM (1/1/1/1 mg/kg and 1 mg/kg/day ip) were most effective. YM and MPSS combination produced no additive effects. YM animals scored better than MPSS and control animals in OFW (Days 8-29) and better than controls on IP (Days 8-29; Day 29) and grid walking (Day 29). MPSS animals scored better than controls on IP (Days 8-29). YM and MPSS groups had greater %TS than controls. This series of experiments demonstrates the utility of this injury model and simple behavioral measures for preclinical assessment of pharmacologic agents. Under these experimental conditions, U74 demonstrated equivalent efficacy to MPSS, and YM demonstrated greater efficacy than MPSS in the treatment of ASCI.

A comparison of YM-14673, U-50488H, and nalmefene after spinal cord injury in the rat.

A reproducible spinal cord injury model was used to compare the efficacy of three compounds previously shown to improve neurologic recovery after injury in rats: The thyrotropin releasing hormone (TRH) analogue, YM-14673; the specific kappa-opioid agonist, U-50488H; and the opioid antagonist, nalmefene, which has increased activity at kappa-receptors. A moderate injury in rats that results in recovery of uncoordinated gross locomotion was made at spinal T9 by rapid displacement (1.1. mm) of the cord. Compounds (or vehicle) were given either by intravenous bolus or by continuous mini-osmotic pump over 7 days, beginning 30 min after the injury as follows: controls (saline), YM-14673 (1 mg/kg bolus), U-50488H (10 mg/kg bolus), U-50488H (0.425 mg/kg/h continuous infusion x 7 days); nalmefene (0.1 mg/kg bolus); and nalmefene (0.021 mg/kg/h continuous infusion x 7 days). Neurologic recovery was assessed for 4 weeks by open-field walking, inclined plane, grid walking, and footprint analysis. The percentage of white matter spared was determined at the lesion epicenter. Only those groups given a bolus of YM14673, U-50488H, and nalmefene had open-field performance better than the scores of controls. Animals that received a bolus of YM-14673 also scored better than controls on the inclined plane and were more likely than controls to recover sufficiently to be tested by both grid walking and footprint analysis. Improved behavioral recovery was not found in groups that received chronic drug infusion. Histology demonstrated significant sparing of white matter for the YM-14673-treated group compared with controls; groups given a U-50488H and nalmefene bolus showed a trend for greater sparing of white matter. The results confirm a beneficial effect for these compounds and suggest that they may be useful in treatment of clinical spinal cord injury.