Muscle Fiber Conduction Velocity and Histopathologic Findings after Intramuscular Injection with 7% Phenol Solution in Rat

OBJECTIVE: To investigate the muscle fiber conduction velocity and histopathologic changes in skeletal muscle after 7% phenol solutions intramuscular injection. METHOD: Forty-five Sprague Dawley rats were divided into two groups: Experimental group, 30; Control group, 15. Experimental and control groups were injected with 0.1 cc of 7% phenol solution and 0.9% saline in right gastrocnemius, respectively. The histopathologic findings and muscle fiber conduction velocity were evaluated at 0, 1, 5, 14, and 28 days after each injection. RESULTS: In the light microscopic examination of experimental groups, vacuolar change, atrophy of myofibers, and intermyofiber cell proliferation were shown. The expression of synaptophysin began to be seen at 5 days and S-100 protein was increased 14 days after injection. In the electron microscopic examination of experimental groups, vacuolar change and denuded postsynaptic membrane were shown. In muscle fiber conduction study of experimental groups, the mean velocity were significantly slowed at 1, 5, 14, and 28 days after injection than those of control groups (p<0.05). CONCLUSION: On the basis of histopathologic findings, it is presumed that the mechanisms of paralysis following intramuscular injection of 7% phenol solutions were both myogenic and neurogenic. The slowing of muscle fiber conduction velocity tended to be related with the histopathologic changes of skeletal muscles after intramuscular injection with 7% phenol solution.

Histopathologic Findings and Muscle Fiber Conduction Studies after Intra-muscular Injection of Botulinum Toxin in Rat

Recently, botulinum toxin has been widely used for the management of spasticity. However it's mechanism of action in the skeletal muscle has not been well clarified. This study was performed to investigate the histopathologic changes in the skeletal muscle after botulinum toxin injection, and to determine the clinical standards of muscle fiber conduction study as an objective indicator for the changes of muscle fiber. As a study group, 35 Sprague Dawley rats were injected intra-muscularly with the botulinum toxin type A around two heads of right gastrocnemius muscle. After the injection of botulinum toxin, histopathologic studies and muscle fiber conduction studies were performed in 5 rats of the study group at 0, 1, 3, 5, 7, 14, and 28th day respectively. Based on the morphologic studies, the mechanisms of paralysis following the botulinum toxin injection were found to be both myogenic and neurogenic, and the motor function recovered through the formation of new motor end-plate and proliferation of Schwann cells. The muscle fiber conduction study revealed that the mean latencies of study group at 1, 3, 5, 7, and 14th day after the injection of botulinum toxin were significantly prolonged than those of the control group(p<0.05). The prolongation and slow recovery of latencies in a muscle fiber conduction study after the injection of botulinum toxin significantly reflect the morphologic changes of paralized skeletal muscles.