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Reduced endplate currents underlie motor unit dysfunction in canine motor neuron disease
Mark M Rich1, Robert F Waldeck, Linda C Cork
1Department of Physiology, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
Journal of Neurophysiology
|December 6, 2002
Summary
Hereditary canine spinal muscular atrophy (HCSMA) in homozygous dogs results from reduced neuromuscular transmission. Decreased neurotransmitter release from motor terminals causes motor unit dysfunction, not axonal issues.
Area of Science:
- Neuroscience
- Canine Genetics
- Motor Neuron Diseases
Background:
- Hereditary canine spinal muscular atrophy (HCSMA) is an autosomal dominant motor neuron disorder.
- Homozygous HCSMA affects motor unit force output and endurance.
- Previous research suggests impaired neuromuscular transmission is the cause.
Purpose of the Study:
- To investigate the underlying mechanisms of motor unit dysfunction in HCSMA.
- To differentiate between neuromuscular transmission deficits and axonal abnormalities.
Main Methods:
- Recorded muscle fiber endplate currents (EPCs) in HCSMA homozygotes and controls.
- Assessed axonal conduction velocity maturation and neurofilament accumulation.
- Examined motor neuron morphology via intracellular labeling.
Main Results:
- EPC amplitudes were reduced with increased failures in HCSMA homozygotes.
- Many HCSMA EPCs fell below the threshold for muscle activation.
- Axonal conduction velocity matured normally, and neurofilament accumulations were minimal.
- Motor neuron and motor unit properties remained correlated.
Conclusions:
- Decreased neurotransmitter release from motor terminals is the primary cause of HCSMA motor unit dysfunction.
- Axonal maturation and structure do not appear to contribute to the observed dysfunction.