Mechanisms regulating the specificity and strength of muscle afferent inputs in the spinal cord

We investigated factors controlling the development of connections between muscle spindle afferents, spinal motor neurons, and inhibitory Renshaw cells. Several mutants were examined to establish the role of muscle spindles, muscle spindle‐derived NT3, and excess NT3 in determining the specificity a...

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Bibliographic Details
Published in:Annals of the New York Academy of Sciences 2010-06, Vol.1198 (1), p.220-230
Main Authors: Mentis, George Z., Alvarez, Francisco J., Shneider, Neil A., Siembab, Valerie C., O'Donovan, Michael J.
Format: Article
Language:English
Subjects:
Afferent Pathways - physiology
Amyotrophic lateral sclerosis
Animals
Axons - physiology
Homeostasis
Interneurons - physiology
Medical research
Mice
motor neuron
Motor Neurons - physiology
muscle spindle
Muscle, Skeletal - innervation
Proprioception - physiology
proprioceptor
Rats
Renshaw
Sensitivity and Specificity
Spinal Cord - physiology
Spinal Nerve Roots - cytology
Spinal Nerve Roots - physiology
stretch reflex
Synapses - physiology
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Summary:We investigated factors controlling the development of connections between muscle spindle afferents, spinal motor neurons, and inhibitory Renshaw cells. Several mutants were examined to establish the role of muscle spindles, muscle spindle‐derived NT3, and excess NT3 in determining the specificity and strength of these connections. The findings suggest that although spindle‐derived factors are not necessary for the initial formation and specificity of the synapses, spindle‐derived NT3 seems necessary for strengthening homonymous connections between Ia afferents and motor neurons during the second postnatal week. We also found evidence for functional monosynaptic connections between sensory afferents and neonatal Renshaw cells although the density of these synapses decreases at P15. We conclude that muscle spindle synapses are weakened on Renshaw cells while they are strengthened on motor neurons. Interestingly, the loss of sensory synapses on Renshaw cells was reversed in mice overexpresssing NT3 in the periphery, suggesting that different levels of NT3 are required for functional maintenance and strengthening of spindle afferent inputs on motor neurons and Renshaw cells.
ISSN:0077-8923
1749-6632
DOI:10.1111/j.1749-6632.2010.05538.x