EXPRESSION OF C-FOS PROTEIN IN THE SPINAL-CORD AFTER BRACHIAL-PLEXUS INJURY - COMPARISON OF ROOT AVULSION AND DISTAL NERVE TRANSECTION

OBJECTIVE: Clinical reports indicate poor outcomes for avulsion injuri es, compared with more peripheral nerve damage. These two different in juries may both affect gene expression in spinal neurons, and the chan ges in gene expression may be related to the types of injuries. METHOD S: The brachial plexus of 48 adult male rats was lesioned by either ro ot avulsion close to the spinal cord or distal nerve transection. The rats were quickly revived and remained awake until death at 30, 60, or 120 min after surgery. In rats with avulsive injuries, traumatic site s on the dorsal and ventral horns of the spinal cord were microscopica lly detected. Immunocytochemical analysis of the c-fos product was per formed for the two experimental groups and for sham-treated control an imals at the same survival times. RESULTS: An increase in Fos-like imm unoreactivity (FLI) in cells of the spinal cord, at levels C4-T1, was detected at 30 min after nerve transection or root avulsion. The numbe r of FLI-positive cells continued to increase at 60 and 120 min after the nerve injury (P = 0.001). FLI-positive cells were compared at the C7 level, in laminae 1 and 2, 3 and 4, and 5 to 10, after the two inju ries and were found to be more abundant after the avulsive injury (P = 0.0001); furthermore, the number of FLI-positive cells increased with time (P = 0.001). In a comparison of ail levels, both experimental gr oups demonstrated significantly greater numbers of FLI-positive cells than did controls, and the group with nerve root avulsion showed signi ficantly (P = 0.0001) more FLI-positive cells than did the group with distal nerve transection. CONCLUSION: These results suggest that nerve root avulsion from the spinal cord leads to increased and prolonged e xpression of c-fos and, potentially, greatly increased transcription o f new messages for recovery, survival, or cell death.