Objective: Botulinum toxin works at the neuromuscular junction by inhibiting the release of acetylcholine from the presynaptic membrane. It has been indicated for limb spasticity in patients with upper motor neuron lesions. The paralytic effect of this toxin usually lasts for 3 to 4 months, and repeated injections are needed to maintain the effect. This study was performed to investigate whether electrical stimulation can prolong the paralytic effect induced by botulinum toxin type A.

Method: Ninety male Sprague-Dawley rats, 30 for control and 60 for experimental, were studied. Botulinum toxin type A (Dysport^Ⱂ) was injected into the gastrocnemius muscle in the experimental groups (10 units for group 1 and 5 units for group 2), and normal saline 0.05 ml was injected into the same muscle in the control group. Thirty minutes of electrical stimulation was applied to the injected muscle with surface-stimulating electrodes. The stimulation was given once a day for 3 times in subgroup E1 and once every other day for 6 times in subgroup E2. No electrical stimulation was applied to subgroup N. Amplitudes of action potentials were measured serially on the injected muscles. At the third week, hematoxylin-eosin stained sections and synaptophysin immunohistochemical stained sections were examined.

Results: 1) At the second week after the toxin injection, amplitudes of action potentials maximally declined to 2.1∼3.7% in group 1 and to 4.0∼5.3% in group 2, compared to the initial amplitude. The amplitudes were beginning to recover from the third week. 2) Electrically stimulated groups demonstrated significantly more depressed amplitudes than non-stimulated group N. These effects lasted till week 2∼4. 3) Hematoxylin-eosin staining for muscle sections showed degenerative changes of muscle fibers. Synaptophysin immunoreactivity in the muscle demonstrated multiple synaptophysin-positive areas in a muscle fiber of the toxin injected muscle.

Conclusion: Transient electrical stimulation to the botulinum toxin injected muscles seems to enhance the paralytic effects of the toxin.

Objective: To quantify the effect of botulinum toxin A injection, by the compound muscle action potential (CMAP) measure from the gastrocnemius muscles (GCM) and to compare them with the clinical data.

Methods: Seventeen legs of 10 cerebral palsy (CP) children were studied with botulinum toxin A injection on the motor points of their GCM. Each GCM was injected up to 6 units of the botulium toxin A per kilogram of the body weight. The CMAP were measured at the motor points of GCM with the surface electrodes on the post-injection day 1, day 3, day 7, 2 weeks and at 1 month then monthly thereafter for 6 months. Physician rating scale (PRS) and the angle of passive ankle dorsiflexion were evaluated at the same time.

Results: The amplitude and the area of the CMAP decreased from post-injection day 1 to 3 months. The most pronounced decrement was seen at 2 weeks post-injection (p＜0.05). The most pronounced increase of the dorsiflexion angle and PRS were seen at 1 and 2 months post-injection, respectively (p＜0.05).

Conclusion: The compound muscle action potential measure can be used for the neurophysiological quantification of the effect of botulinum toxin A, especially for the superficial muscles of extremities.

Botulinum toxin develops muscular paralysis through the inhibition of acetylcholine release from presynaptic membrane in neuromuscular junction. It has been used clinically to treat strabismus, blepharospasm and spasmodic dysphonia. Recently it was introduced for the treatment of limb spasticity as well. Serial compound muscle action potential(CMAP) amplitudes were measured and repetitive nerve stimulation test(RNST) was performed with 2Hz and 30Hz on the rat gastrocnemius muscle to observe the effect of muscle paralysis. Also, Periodic acid Schiff (PAS) staining sections of the muscle for glycogen was studied to quantify the degree of muscular paralysis.

Thirty Sprague-Dawley rats, 10 for control and 20 for experimental group were studied for 12 weeks. Normal saline 0.025 ml and 0.125 ml was injected into gastrocnemius muscle in cotrol group 1 and 2, respectively. Botulinum toxin type A(Botox) was injected 5.0U/0.025 ml in experimental group 1, 2.5U/0.025 ml in group 2, 2.5U/0.125 ml in group 3, and 0.5U/0.025 ml in group 4. The amplitudes of CMAP declined markedly by 81.1% to 96.5% of basal amplitudes on the first week after Botox injection, but slightly recovered on 12th week by 20.8% to 42.2% with greater recovery in lower dose group. RNST with 2Hz produced no remarkable 1 : 5 amplitude change in experimental group. RNST with 30Hz produced marked increment in 1 : 5 amplitude up to 24.4%. PAS staining for muscle sections showed residual glycogen after tetanic stimulation due to neuromuscular block by Botox.