Decreased dynorphin A (1-17) in the spinal cord of spastic rats after the compressive injury.

Spasticity in rat hindlimbs was induced by compressing cervical spinal cord with a wax ball. Ashworth score and H-reflex were measured 1 week after the surgery. The results showed that: (1) muscle spasm was detected in the hindlimbs a week after the operation and maintained at least 8 weeks, (2) in the spastic animals, dynorphin A (1-17)-ir decreased significantly in thoracic and lumbar segments of the spinal cord and (3) peripheral administration of kappa receptor agonist U50488H and electrical stimulation at 100 Hz effectively relieved the muscle spasm. Our data supported the note that the reduction of endogenous dynorphin A (1-17) might play an important role in the pathogenesis of spinally induced muscle spasticity and the replenishment of its shortage might relieve the spasticity.