THE EFFECT OF BOTULINUM TOXIN TYPE-A INJECTION ON COMPOUND MUSCLE ACTION-POTENTIAL IN AN IN-VIVO RAT MODEL

Serial measurements were performed on the compound muscle action poten tial (CMAP) amplitude and the force generated by the rat lower hind li mb flexors to investigate the time course of intramuscular injections of botulinum toxin type A (BOTOX(R)). Thirty animals were used in this in vivo rat model. CMAP amplitude and muscle force were measured at p redetermined intervals for 28 weeks. Compound muscle action potential amplitude and force declined markedly the first 5 to 7 days after inje ction of BOTOX but recovered in a near linear manner, The response mag nitude and recovery rate were dose-dependent. Recovery of CMAP amplitu de preceded recovery of muscle force. No clear evidence of a systemic effect on the untreated leg or a concentration effect was found. CMAP amplitude may be useful in determining optimal timing of repeat inject ions in treating neuromuscular disorders.