Effects of 4-aminopyridine on muscle and motor unit force in canine motor neuron disease

• Type of Material: Article
• Authors: Martin Pinter, Emory University; R. F. Waldeck, Allegheny University; Timothy Cope, Emory University; L. C. Cork, Stanford University
• Language: English
• Date: 1997-06-01
• Publisher: Lippincott, Williams & Wilkins
• Publication Version: Final Published Version
• Copyright Statement: Copyright © 1997 Society for Neuroscience
• License: Creative Commons Attribution 4.0 International
• Final Published Version (URL): http://dx.doi.org/10.1523/JNEUROSCI.17-11-04500.1997
• Title of Journal or Parent Work: Journal of Neuroscience Nursing
• ISSN: 0888-0395
• Volume: 17
• Issue: 11
• Start Page: 4500
• End Page: 4507
• Grant/Funding Information: We thank Drs. Donald Faber and Rita Balice-Gordon for helpful comments on this manuscript.; The Hereditary Canine Spinal Muscular Atrophy breeding colony was supported in part by Public Health Service Grant NS10580 to Dr. Donald L. Price.; This work was supported by National Institutes of Health (Grants NS31621, NS07287, NS31563).
• Keywords: Neurosciences & Neurology; POTENTIATION; AMYOTROPHIC-LATERAL-SCLEROSIS; NEUROMUSCULAR-TRANSMISSION; Life Sciences & Biomedicine; RESIDUAL CALCIUM; neuromuscular disease; potassium channel; transmitter release; muscle force; SPINAL MUSCULAR-ATROPHY; synaptic transmission; 3,4-DIAMINOPYRIDINE; TRANSMITTER RELEASE; SYNAPTIC TRANSMISSION; Science & Technology; NERVE-TERMINALS; calcium influx; CAT; Neurosciences
• Research Categories: Biology, Physiology; Biology, Neuroscience

Abstract

Hereditary Canine Spinal Muscular Atrophy (HCSMA) is an autosomal dominant disorder of motor neurons that shares features with human motor neuron disease. In animals exhibiting the accelerated phenotype (homozygotes), we demonstrated previously that many motor units exhibit functional deficits that likely reflect underlying deficits in neurotransmission. The drug 4-aminopyridine (4AP) blocks voltage-dependent potassium conductances and is capable of increasing neurotransmission by overcoming axonal conduction block or by increasing transmitter release. In this study, we determined whether and to what extent 4AP could enhance muscle force production in HCSMA. Systemic 4AP (1-2 mg/kg) increased nerve-evoked whole muscle twitch force and electromyograms (EMG) to a greater extent in older homozygous animals than in similarly aged, symptomless HCSMA animals or in one younger homozygous animal. The possibility that this difference was caused by the presence of failing motor units in the muscles from homozygotes was tested directly by administering 4AP while recording force produced by failing motor units. The results showed that the twitch force and EMG of failing motor units could be significantly increased by 4AP, whereas no effect was observed in a nonfailing motor unit from a symptomless, aged- matched HCSMA animal. The ability of 4AP to increase force in failing units may be related to the extent of failure. Although 4AP increased peak forces during unit tetanic activation, tetanic force failure was not eliminated. These results demonstrate that the force outputs of failing motor units in HCSMA homozygotes can be increased by 4AP. Possible sites of 4AP action are considered.