A small skin incision was made longitudinally on the medial part of the elbow to expose the ulnar nerve under isoflurane anesthesia. The ulnar nerve was bilaterally ligated with 4–0 silk and cut around the medial head of the triceps muscle of both forelimbs. Forty-eight to 72 hr after the nerve injury, the rats were subjected to the locomotor activity test following acute cocaine injection.