Journal of Neuroscience, Vol 2, 654-652, Copyright © 1982 by Society for Neuroscience
Anatomical and behavioral recovery from the effects of spinal cord transection: dependence on metamorphosis in anuran larvae
CJ Forehand and PB Farel
This study of spinal cord injury in bullfrog (Rana catesbeiana) tadpoles
using the neuroanatomical tracer horseradish peroxidase (HRP) was
undertaken to determine (1) whether the same anatomical regions that
normally give rise to ascending or descending spinal tracts do so following
complete spinal cord transection and (2) whether the course of behavioral
recovery could be related to the anatomical results. The results of this
study show that (1) spinal cord continuity is readily restored in tadpoles
subjected to spinal cord transection, but nerve fibers crossing the site of
injury end within 1 to 2 mm of the lesion site; (2) tadpoles with spinal
cord transections held through metamorphosis show, as juvenile frogs,
restoration of lumbar projections from all brainstem regions that normally
project to the lumbar spinal cord; (3) neither long ascending projections
from dorsal root ganglion cells nor those from spinal neurons caudal to the
transection traverse the transection site, even after metamorphosis; and
(4) consistent with the anatomical results, tadpoles show only minimal
behavioral recovery, but these same animals as juvenile frogs show recovery
of behaviors that are dependent upon connections to supraspinal regions. In
other experiments, [3H]thymidine or [3H]apo-HRP was combined with HRP
histochemistry to determine if new brainstem neurons projecting to the
spinal cord are born in the metamorphic period and if, in normal animals,
brainstem projections to the lumbar spinal cord persist through
metamorphosis. We found no evidence that neurons with lumbar spinal cord
projections are born during metamorphosis; however, evidence was found that
most brainstem neurons that project to the lumbar spinal cord before
metamorphosis retain this projection in the juvenile frog.