Nerve Influence on Rat Fast-Twitch Skeletal Muscle Regeneration

The degeneration-regeneration process induced by bupivacaine injection has been studied in rat extensor digitorum longus (EDL) muscle in the presence or absence of nerve, the presence of tetrodotoxin (TTX)-induced block of nerve impulse conduction, and the presence of vin-blastine-induced block of nerve axoplasmic flow associated to TTX block. Seven and 14 days after bupivacaine injection, myosin heavy chain (MHC) expression was analysed by immu-nohistochemistry and Western blot. Type 1 MHC isoform expression was almost completely dependent on nerve impulse discharge. Expression of the type 2A showed a zonal distribution in denervated muscles, and a marked down-regulation in the TTX-paralysed, but not in TTX-vinblastine-treated muscles. These results show that expression of type 2A isoform in inner-vated-regenerated fast muscle is mainly due to neuromotor activity. They also suggest that 2A isoform expression is inhibited by a chemical factor carried by axoplasmic flow. Key words: fast skeletal muscle, myosin heavy chains, nerve activity block, neurotrophic factors, regeneration. Basic Appl Myol 12 (4): 219-225, 200