4-Aminopyridine enhances motor evoked potentials following graded spinal cord compression injury in rats

Although several experimental and clinical studies have demonstrated the ability of 4-aminopyridine (4-AP) to restore electrophysiological and/or behavioral function following chronic spinal cord injury, the mechanism by which this occurs remains unclear. Demonstration of efficacy in rat spinal cord injury has not been reported, evidently because even relatively mild spinal cord contusions that produce only minor permanent locomotor disturbances abolish hind limb myoelectric motor evoked potentials (mMEPs). In this study, mMEPs were recorded acutely 25 days following graded thoracic spinal cord compression in rats. mMEP amplitudes were significantly enhanced by a single, 2 mg/kg i.v. dose of 4-AP. mMEPs were increased in all rats showing some evoked responses initially, and also in some animals which had no responses prior to treatment. 4-AP was further found to increase the maximum following frequency of mMEPs in both normal and injured rats from about 0.1 Hz to between 1 and 10 Hz. These data suggest that 4-AP might act by enhancing synaptic efficacy, as well as enhancing conduction in spinal axons whose myelination has been rendered dysfunctional by trauma.