Effectiveness of riluzole in suppressing spasticity in the spinal cord injured rat

Spasticity poses a major detrimental impact on the quality of life in a significant number of people with spinal cord injury (SCI). Recent observations in our laboratory suggest that spinal transection at the sacral S₂ level induces a significant increase in glutamatergic input to sacrocaudal motoneurons during the time spasticity is present in the tail muscles. The present study examined the effectiveness of riluzole, an agent that has been shown to reduce glutamate release, in managing spasticity within the tail musculature. In this blinded, cross-over study animals with S₂ spinal transections were tested behaviorally for the progression of spasticity in the tail musculature using our established system. When the animals demonstrated a significant level of spastic behavior (e.g. increased response to quick stretch, noxious and non-noxious cutaneous stimuli), they received either saline or riluzole (8 or 10 mg/kg i.p.) and assessed behaviorally at 1, 3, 6, and 12 post-injection. Results: riluzole at 8 mg/kg significantly decreased the response of the tail muscle to noxious and non-noxious cutaneous stimuli for the first 3 h post-administration, while administration of riluzole at 10 mg/kg significantly decreased the responsiveness of the tail to all of the behavioral assessments. However, a significant percentage of the animals displayed motor impairments at this higher dosage. Conclusion: suppression of glutamate release by the administration of riluzole can reduce several, but not all, aspects of spastic activity in the tail muscles at concentrations that do not elicit negative side-effects.