Journal of Neuroscience, Vol 3, 243-251, Copyright © 1983 by Society for Neuroscience
Correlation of axonal regeneration and slow component B in two branches of a single axon
JR Wujek and RJ Lasek
We investigated the relationship between slow axonal transport and axonal
regeneration in the rat dorsal root ganglion (DRG) cell. The DRG cell sends
out a single axon which bifurcates within the ganglion; one axon proceeds
centrally into the spinal cord and the other proceeds peripherally. The
rate of axonal regeneration is approximately 2 times faster for the
peripheral processes (4.6 +/- 0.9 mm/day) than for the central processes
(2.1 +/- 0.5 mm/day). The peripheral and central processes regenerate
through dissimilar environments (sciatic nerve and dorsal root,
respectively); thus, environmental factors may account for the differences
in regeneration rates. We tested this possibility by measuring the
regeneration of motoneuron axons within the ventral root (histologically
similar to the dorsal root). The motoneuron regeneration rate within the
ventral root is similar to the motoneuron regeneration rate within the
sciatic nerve, suggesting that factors within the DRG cell produce the
differences in regeneration rate. Slow axonal transport is classified into
two distinct components: slow component a (SCa), corresponding to the
microtubule/neurofilament network of the axonal cytoskeleton, and slow
component b (SCb), corresponding to the microfilament complex/axoplasmic
matrix. The transport rate of SCa and SCb in the peripheral sensory axons
is approximately 2 times faster than their counterparts in the central
sensory axons. SCa moves at 1.0 to 3.0 mm/day in the peripheral processes
and 0.5 to 1.0 mm/day in the central processes; SCb moves at 3.5 to 6.5
mm/day in the peripheral processes and 2.0 to 3.5 mm/day in the central
processes. In each branch of the DRG cell, the rate of axonal regeneration
is similar to the rate of SCb transport. These results support the
hypothesis that SCb is a rate-limiting factor in axonal regeneration
because of its role in providing the cytoskeletal elements which are
directly involved in the motility of the growth cone and elongation of the
axon.
