Positional Strategies for Connection Specificity and Synaptic Organization in Spinal Sensory-Motor Circuits

Neuron. 2019 Jun 19;102(6):1143-1156.e4. doi: 10.1016/j.neuron.2019.04.008. Epub 2019 May 7.


Proprioceptive sensory axons in the spinal cord form selective connections with motor neuron partners, but the strategies that confer such selectivity remain uncertain. We show that muscle-specific sensory axons project to motor neurons along topographically organized angular trajectories and that motor pools exhibit diverse dendritic arbors. On the basis of spatial constraints on axo-dendritic interactions, we propose positional strategies that can account for sensory-motor connectivity and synaptic organization. These strategies rely on two patterning principles. First, the degree of axo-dendritic overlap reduces the number of potential post-synaptic partners. Second, a close correlation between the small angle of axo-dendritic approach and the formation of synaptic clusters imposes specificity of connections when sensory axons intersect multiple motor pools with overlapping dendritic arbors. Our study identifies positional strategies with prominent roles in the organization of spinal sensory-motor circuits.

Keywords: axonal trajectory; dendrites; motor control; motor neurons; positional factors; proprioceptors; sensory-motor connectivity; spinal cord; synaptic organization.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Axons
  • Buttocks
  • Dendrites
  • Foot
  • Hindlimb
  • Mice
  • Microscopy, Confocal
  • Motor Neurons / cytology
  • Motor Neurons / physiology*
  • Muscle, Skeletal / innervation*
  • Proprioception
  • Sensory Receptor Cells / cytology
  • Sensory Receptor Cells / physiology*
  • Spinal Cord / anatomy & histology
  • Spinal Cord / physiology*
  • Synapses / physiology*