Motor neuron-specific overexpression of the presynaptic choline transporter: impact on motor endurance and evoked muscle activity.

Lund D, Ruggiero AM, Ferguson SM, Wright J, English BA, Reisz PA, Whitaker SM, Peltier AC, Blakely RD
Neuroscience. 2010 171 (4): 1041-53

PMID: 20888396 · PMCID: PMC2992794 · DOI:10.1016/j.neuroscience.2010.09.057

The presynaptic, hemicholinium-3 sensitive, high-affinity choline transporter (CHT) supplies choline for acetylcholine (ACh) synthesis. In mice, a homozygous deletion of CHT (CHT-/-) leads to premature cessation of spontaneous or evoked neuromuscular signaling and is associated with perinatal cyanosis and lethality within 1 h. Heterozygous (CHT+/-) mice exhibit diminished brain ACh levels and demonstrate an inability to sustain vigorous motor activity. We sought to explore the contribution of CHT gene dosage to motor function in greater detail using transgenic mice where CHT is expressed under control of the motor neuron promoter Hb9 (Hb9:CHT). On a CHT-/- background, the Hb9:CHT transgene conferred mice with the ability to move and breath for a postnatal period of ∼24 h, thus increasing survival. Conversely, Hb9:CHT expression on a wild-type background (CHT+/+;Hb9:CHT) leads to an increased capacity for treadmill running compared to wild-type littermates. Analysis of the stimulated compound muscle action potential (CMAP) in these animals under basal conditions established that CHT+/+;Hb9:CHT mice display an unexpected, bidirectional change, producing either elevated or reduced CMAP amplitude, relative to CHT+/+ animals. To examine whether these two groups arise from underlying changes in synaptic properties, we used high-frequency stimulation of motor axons to assess CMAP recovery kinetics. Although CHT+/+; Hb9:CHT mice in the two groups display an equivalent, time-dependent reduction in CMAP amplitude, animals with a higher basal CMAP amplitude demonstrate a significantly enhanced rate of recovery. To explain our findings, we propose a model whereby CHT support for neuromuscular signaling involves contributions to ACh synthesis as well as cholinergic synaptic vesicle availability.

Copyright © 2010 IBRO. Published by Elsevier Ltd. All rights reserved.

MeSH Terms (25)

Acetylcholine Acetylcholinesterase Action Potentials Animals Animals, Newborn Behavior, Animal Brain Choline O-Acetyltransferase Electric Stimulation Exercise Test Gene Expression Regulation, Developmental GPI-Linked Proteins Green Fluorescent Proteins Homeodomain Proteins Membrane Transport Proteins Mice Mice, Transgenic Motor Activity Motor Neurons Muscle, Skeletal Nerve Tissue Proteins Neuromuscular Junction Statistics, Nonparametric Synapses Transcription Factors

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