Enhanced brain motor activity in patients with MS after a single dose of 3,4-diaminopyridine C. Mainero, MD; M. Inghilleri, MD; P. Pantano, MD; A. Conte, MD; D. Lenzi, MD; V. Frasca, MD; L. Bozzao, MD; and C. Pozzilli, MD Abstract—Background: 3,4-Diaminopyridine (3,4-DAP), a potassium (K + ) channel blocker, improves fatigue and motor function in multiple sclerosis (MS). Although it was thought to do so by restoring conduction to demyelinated axons, recent experimental data show that aminopyridines administered at clinical doses potentiate synaptic transmission. Objective: To investigate motor cerebral activity with fMRI and transcranial magnetic stimulation (TMS) after a single oral dose of 3,4-DAP in patients with MS. Methods: Twelve right-handed women (mean  SD age 40.9  9.3 years) underwent fMRI on two separate occasions (under 3,4-DAP and under placebo) during a simple motor task with the right hand. FMRI data were analyzed with SPM99. After fMRI, patients underwent single-pulse TMS to test motor threshold, amplitude, and latency of motor evoked potentials, central conduction time, and the cortical silent period; paired-pulse TMS to investigate intracortical inhibition (ICI) and intracortical facilitation (ICF); and quantitative electromyography during maximal voluntary contraction. Results: FMRI motor-evoked brain activation was greater under 3,4-DAP than under placebo in the ipsilateral sensorimotor cortex and supplementary motor area (p  0.05). 3,4-DAP decreased ICI and increased ICF; central motor conduction time and muscular fatigability did not change. Conclusion: 3,4-DAP may modulate brain motor activity in patients with MS, probably by enhancing excitatory synaptic transmission. NEUROLOGY 2004;62:2044 –2050 The potassium (K + ) channel– blocking agent 4-aminopyridine (4-AP) and its related compound 3,4-diaminopyridine (DAP) improve fatigue and mo- tor weakness in patients with multiple sclerosis (MS). 1-4 Although early experimental data suggested that APs improve the symptoms of MS by restoring conduction to demyelinated axons, 5 the findings were unreliable because the dose used experimentally was 250 to 1,000 times higher than that used in clinical trials. Recent experimental data have shown that although 4-AP administered at clinical doses fails to restore conduction to demyelinated axons, it potenti- ates synaptic transmission and increases skeletal muscle twitch tension. 6 Electrophysiologic studies in patients with MS have also failed to show that APs improve central motor conduction. 3,4 Hence, APs may induce their beneficial effects in MS primarily by not acting on the unmyelinated portion of axons but by modulating synaptic transmission. Neural activity can be studied in humans in vivo and noninvasively using various techniques includ- ing blood oxygen level– dependent (BOLD) fMRI and transcranial magnetic stimulation (TMS). FMRI has been used to investigate brain activation in response to pharmacologic 7 and behavioral 8 interventions. Previous fMRI studies have shown cortical and sub- cortical changes related to motor tasks in patients with MS with various degrees of clinical disability. 9-11 These changes partly reflect the underlying brain damage, thus providing a rationale for the use of pharmacologic methods to reduce neuronal damage or to enhance brain plasticity in MS. 12 Although fMRI could be a useful tool for evaluating 3,4-DAP- induced cortical and subcortical motor changes, this technique measures neuronal activation only indi- rectly, providing an index of energy expenditure sec- ondary to excitatory or inhibitory synaptic activity. 13 Motor cortex excitability can be tested directly by paired-pulse TMS. 14 Paired-pulse stimulation has provided useful information on the effects of various neurotrophic drugs on cortical excitability in healthy subjects 15-17 but not in MS. Despite its strengths, as a method for localizing sources of brain activity and providing information on the overall extension of brain motor networks, TMS is far more limited than fMRI. In this double-blind, placebo-controlled, cross-over study, we used fMRI and paired-pulse TMS to inves- tigate changes in cerebral motor activation and mo- tor cortex excitability after a single oral dose of 3,4- DAP in 12 patients who were mildly disabled with From the Sections of Clinical Neurology (Drs. Mainero, Inghilleri, Conte, Lenzi, Frasca, and Pozzilli) and Neuroradiology (Drs. Pantano and Bozzao), Department of Neurological Sciences, University of Rome “La Sapienza,” Italy. Supported partially by Ministero della Salute (RF01.167), Italy. Received August 14, 2003. Accepted in final form February 3, 2004. Address correspondence and reprint requests to Dr. C. Mainero (c/o Carlo Pozzilli), Department of Neurologic Sciences, University of Rome “La Sapienza,” Viale dell’Università, 30, I-00185, Rome, Italy; e-mail: caterina.mainero@uniroma1.it 2044 Copyright © 2004 by AAN Enterprises, Inc.