Hyperexcitability precedes motoneuron loss in the Smn mouse model of spinal muscular atrophy. 2019

K A Quinlan, and E J Reedich, and W D Arnold, and A C Puritz, and C F Cavarsan, and C J Heckman, and C J DiDonato
Department of Biomedical and Pharmaceutical Sciences, College of Pharmacy, University of Rhode Island, Kingston, Rhode Island.

Spinal motoneuron dysfunction and loss are pathological hallmarks of the neuromuscular disease spinal muscular atrophy (SMA). Changes in motoneuron physiological function precede cell death, but how these alterations vary with disease severity and motoneuron maturational state is unknown. To address this question, we assessed the electrophysiology and morphology of spinal motoneurons of presymptomatic Smn mice older than 1 wk of age and tracked the timing of motor unit loss in this model using motor unit number estimation (MUNE). In contrast to other commonly used SMA mouse models, Smn mice exhibit more typical postnatal development until postnatal day (P)11 or 12 and have longer survival (~3 wk of age). We demonstrate that Smn motoneuron hyperexcitability, marked by hyperpolarization of the threshold voltage for action potential firing, was present at P9-10 and preceded the loss of motor units. Using MUNE studies, we determined that motor unit loss in this mouse model occurred 2 wk after birth. Smn motoneurons were also larger in size, which may reflect compensatory changes taking place during postnatal development. This work suggests that motoneuron hyperexcitability, marked by a reduced threshold for action potential firing, is a pathological change preceding motoneuron loss that is common to multiple models of severe SMA with different motoneuron maturational states. Our results indicate voltage-gated sodium channel activity may be altered in the disease process.NEW & NOTEWORTHY Changes in spinal motoneuron physiologic function precede cell death in spinal muscular atrophy (SMA), but how they vary with maturational state and disease severity remains unknown. This study characterized motoneuron and neuromuscular electrophysiology from the Smn model of SMA. Motoneurons were hyperexcitable at postnatal day (P)9-10, and specific electrophysiological changes in Smn motoneurons preceded functional motor unit loss at P14, as determined by motor unit number estimation studies.

UI MeSH Term Description Entries
D009046 Motor Neurons Neurons which activate MUSCLE CELLS. Neurons, Motor,Alpha Motorneurons,Motoneurons,Motor Neurons, Alpha,Neurons, Alpha Motor,Alpha Motor Neuron,Alpha Motor Neurons,Alpha Motorneuron,Motoneuron,Motor Neuron,Motor Neuron, Alpha,Motorneuron, Alpha,Motorneurons, Alpha,Neuron, Alpha Motor,Neuron, Motor
D009134 Muscular Atrophy, Spinal A group of disorders marked by progressive degeneration of motor neurons in the spinal cord resulting in weakness and muscular atrophy, usually without evidence of injury to the corticospinal tracts. Diseases in this category include Werdnig-Hoffmann disease and later onset SPINAL MUSCULAR ATROPHIES OF CHILDHOOD, most of which are hereditary. (Adams et al., Principles of Neurology, 6th ed, p1089) Bulbospinal Neuronopathy,Oculopharyngeal Spinal Muscular Atrophy,Progressive Muscular Atrophy,Scapuloperoneal Form of Spinal Muscular Atrophy,Spinal Muscular Atrophy,Adult Spinal Muscular Atrophy,Adult-Onset Spinal Muscular Atrophy,Amyotrophy, Neurogenic Scapuloperoneal, New England Type,Distal Spinal Muscular Atrophy,Hereditary Motor Neuronopathy,Muscular Atrophy, Adult Spinal,Myelopathic Muscular Atrophy,Myelopathic Muscular Atrophy, Progressive,Progressive Myelopathic Muscular Atrophy,Progressive Proximal Myelopathic Muscular Atrophy,Proximal Myelopathic Muscular Atrophy, Progressive,Scapuloperoneal Spinal Muscular Atrophy,Spinal Amyotrophy,Spinal Muscular Atrophy, Distal,Spinal Muscular Atrophy, Oculopharyngeal,Spinal Muscular Atrophy, Scapuloperoneal,Spinal Muscular Atrophy, Scapuloperoneal Form,Adult Onset Spinal Muscular Atrophy,Amyotrophies, Spinal,Amyotrophy, Spinal,Atrophies, Progressive Muscular,Atrophy, Myelopathic Muscular,Atrophy, Progressive Muscular,Atrophy, Spinal Muscular,Bulbospinal Neuronopathies,Hereditary Motor Neuronopathies,Motor Neuronopathies, Hereditary,Motor Neuronopathy, Hereditary,Muscular Atrophies, Progressive,Muscular Atrophy, Myelopathic,Muscular Atrophy, Progressive,Neuronopathies, Bulbospinal,Neuronopathies, Hereditary Motor,Neuronopathy, Bulbospinal,Neuronopathy, Hereditary Motor,Progressive Muscular Atrophies,Spinal Amyotrophies
D004195 Disease Models, Animal Naturally-occurring or experimentally-induced animal diseases with pathological processes analogous to human diseases. Animal Disease Model,Animal Disease Models,Disease Model, Animal
D000200 Action Potentials Abrupt changes in the membrane potential that sweep along the CELL MEMBRANE of excitable cells in response to excitation stimuli. Spike Potentials,Nerve Impulses,Action Potential,Impulse, Nerve,Impulses, Nerve,Nerve Impulse,Potential, Action,Potential, Spike,Potentials, Action,Potentials, Spike,Spike Potential
D000818 Animals Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA. Animal,Metazoa,Animalia
D055533 Survival of Motor Neuron 1 Protein An SMN complex protein that contains a TUDOR DOMAIN and is essential for the function of the SMN protein complex. In humans, the protein is encoded by a single gene found near the inversion TELOMERE of a large inverted region of CHROMOSOME 5. Mutations in the gene coding for survival of motor neuron 1 protein may result in SPINAL MUSCULAR ATROPHIES OF CHILDHOOD. SMN Protein (Spinal Muscular Atrophy),Survival Motor Neuron Protein 1,Survival of Motor Neuron 1, Telomeric Protein
D018345 Mice, Knockout Strains of mice in which certain GENES of their GENOMES have been disrupted, or "knocked-out". To produce knockouts, using RECOMBINANT DNA technology, the normal DNA sequence of the gene being studied is altered to prevent synthesis of a normal gene product. Cloned cells in which this DNA alteration is successful are then injected into mouse EMBRYOS to produce chimeric mice. The chimeric mice are then bred to yield a strain in which all the cells of the mouse contain the disrupted gene. Knockout mice are used as EXPERIMENTAL ANIMAL MODELS for diseases (DISEASE MODELS, ANIMAL) and to clarify the functions of the genes. Knockout Mice,Mice, Knock-out,Mouse, Knockout,Knock-out Mice,Knockout Mouse,Mice, Knock out
D018482 Muscle, Skeletal A subtype of striated muscle, attached by TENDONS to the SKELETON. Skeletal muscles are innervated and their movement can be consciously controlled. They are also called voluntary muscles. Anterior Tibial Muscle,Gastrocnemius Muscle,Muscle, Voluntary,Plantaris Muscle,Skeletal Muscle,Soleus Muscle,Muscle, Anterior Tibial,Muscle, Gastrocnemius,Muscle, Plantaris,Muscle, Soleus,Muscles, Skeletal,Muscles, Voluntary,Skeletal Muscles,Tibial Muscle, Anterior,Voluntary Muscle,Voluntary Muscles

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