Journal of Neuroscience, Vol 6, 2757-2763, Copyright © 1986 by Society for Neuroscience
Selective innervation of transplanted limb muscles by regenerating motor axons in the axolotl
DJ Wigston
The segmental pattern of motor innervation of hindlimb muscles in the
axolotl was studied before and after reinnervation. To ascertain the
specificity of reinnervation, the four spinal nerves innervating the
hindlimb were severed and allowed to regenerate. The segmental origin of
axons reinnervating particular muscles was then determined by intracellular
recording from muscle fibers. Muscles were reinnervated in a specific
manner: From the outset, the axons reinnervating each muscle originated
largely from segmentally appropriate spinal nerves in the proper
proportions, suggesting that a reliable mechanism of selective synapse
regeneration exists even in mature axolotls. To examine the selectivity of
reinnervation, individual muscles were transplanted to novel positions
within the limb and the specificity of their reinnervation determined. Even
after being moved to new positions, muscles were reinnervated for the most
part by axons of appropriate segmental origin. Therefore, cues must exist
on or within limb muscles that regenerating motor axons recognize and use
to discriminate between different muscles during synapse formation. These
results suggest that one of the mechanisms that promote the reestablishment
of correct connections during reinnervation of axolotl limbs may be the
selective formation of synapses with appropriate target cells.