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Author Notes:

Correspondence should be addressed to Dr Francisco Alvarez, Emory University, 615 Michael Street, Atlanta, GA 30322., Email: francisco.j.alvarez@emory.edu

.M.R. and F.J.A. designed research; T.M.R., P.N., and F.J.A. performed research; T.M.R. and F.J.A. analyzed data; T.M.R., T.C.C., and F.J.A. wrote the paper.

We thank Dr P.K. Rose for helpful discussions and sharing their COM analysis programs, and Lori Goss, Registered Veterinary Technician, for excellent technical assistance during nerve surgeries and veterinary care of the animals.

The authors declare no competing financial interests.

Subjects:

Research Funding:

This work was supported by NIH Program Project Grant P01NS057228.

Keywords:

  • Science & Technology
  • Life Sciences & Biomedicine
  • Neurosciences
  • Neurosciences & Neurology
  • NEUROSCIENCES
  • axotomy
  • IA afferents
  • nerve transection
  • regeneration
  • spinal cord
  • stretch reflex
  • GROUP-IA SYNAPSES
  • CENTRAL SYNAPTIC DISCONNECTION
  • PERSISTENT INWARD CURRENTS
  • REINNERVATED MOTOR UNITS
  • ALPHA-MOTONEURONS
  • HORSERADISH-PEROXIDASE
  • AXOTOMIZED MOTONEURONS
  • MEDIAL GASTROCNEMIUS
  • SPLENIUS MOTONEURONS
  • HINDLIMB KINEMATICS

Normal Distribution of VGLUT1 Synapses on Spinal Motoneuron Dendrites and Their Reorganization after Nerve Injury

Tools:

Journal Title:

Journal of Neuroscience

Volume:

Volume 34, Number 10

Publisher:

, Pages 3475-3492

Type of Work:

Article | Final Publisher PDF

Abstract:

Peripheral nerve injury induces permanent alterations in spinal cord circuitries that are not reversed by regeneration. Nerve injury provokes the loss of many proprioceptive IA afferent synapses (VGLUT1-IR boutons) from motoneurons, the reduction of IA EPSPs in motoneurons, and the disappearance of stretch reflexes. After motor and sensory axons successfully reinnervate muscle, lost IA VGLUT1 synapses are not re-established and the stretch reflex does not recover; however, electrically evoked EPSPs do recover. The reasons why remaining IA synapses can evoke EPSPs on motoneurons, but fail to transmit useful stretch signals are unknown. To better understand changes in the organization of VGLUT1 IA synapses that might influence their input strength, we analyzed their distribution over the entire dendritic arbor of motoneurons before and after nerve injury. Adult rats underwent complete tibial nerve transection followed by microsurgical reattachment and 1 year later motoneurons were intracellularly recorded and filled with neurobiotin to map the distribution of VGLUT1 synapses along their dendrites. We found in control motoneurons an average of 911 VGLUT1 synapses; ~62% of them were lost after injury. In controls, VGLUT1 synapses were focused to proximal dendrites where they were grouped in tight clusters. After injury, most synaptic loses occurred in the proximal dendrites and remaining synapses were declustered, smaller, and uniformly distributed throughout the dendritic arbor. We conclude that this loss and reorganization renders IA afferent synapses incompetent for efficient motoneuron synaptic depolarization in response to natural stretch, while still capable of eliciting EPSPs when synchronously fired by electrical volleys.

Copyright information:

© 2014 the authors.

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