Journal of Neuroscience, Vol 4, 2784-2791, Copyright © 1984 by Society for Neuroscience
Regeneration of sensory-motor synapses in the spinal cord of the bullfrog
DW Sah and E Frank
Sensory fibers innervating muscles in the arm of the bullfrog form specific
patterns of monosynaptic connections with motoneurons in the spinal cord.
We show here that these normal patterns are re-established after
interruption of the second dorsal root (DR2) in tadpoles and
postmetamorphic frogs. DR2 was either cut or crushed, and 2 to 8 months
later the extent and specificity of regeneration were assessed anatomically
and physiologically. Horseradish peroxidase labeling of DR2 showed that
sensory afferents had regenerated back into the spinal cord to form local
arborizations, as in the normal adult. However, few long-tract fibers in
the dorsal columns regenerated. Intracellular recording from different
classes of motoneurons at the level of DR2 revealed that triceps muscle
sensory afferents had regenerated to form functionally appropriate
synapses. As in the normal adult, stimulation of the triceps nerves
elicited larger monosynaptic EPSPs in triceps motoneurons than in
non-triceps motoneurons. Thus, in the central nervous system of the
bullfrog, specific monosynaptic connections are re-formed within the region
of local regeneration.
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