Journal of Neuroscience, Vol 15, 8191-8198, Copyright © 1995 by Society for Neuroscience
Peripheral target specification of synaptic connectivity of muscle spindle sensory neurons with spinal motoneurons
P Wenner and E Frank
Neurobiology Department, University of Pittsburgh, School of Medicine, Pennsylvania 15261, USA.
The source of environmental cues determining the central connections of
muscle sensory neurons was investigated by manipulating chick embryos so
that sensory neurons supplied a duplicate set of dorsal thigh muscles.
These neurons projected out ventral nerve pathways and along motor axons
that normally project to ventral muscles but their ultimate target tissue
was the duplicate set of dorsal muscles. The central connections of these
sensory neurons to motoneurons supplying normal dorsal muscles were then
determined with intracellular recordings in isolated spinal cord
preparations. Sensory neurons supplying individual duplicate dorsal muscles
made the same connections as those supplying the corresponding normal
dorsal muscles; the pattern of these connections was different than that
made by afferents supplying ventral muscles. Sensory neurons thus made
synaptic connections appropriate for their target muscle rather than for
their more proximal ventral environment. These findings suggest that the
target muscle is the source of cues that determine the central connections
of the sensory neurons projecting to it. Motoneurons forced to innervate
novel muscle received many of the same sensory inputs they would normally
receive, suggesting that motoneurons are less influenced by their target
tissue than sensory neurons.