Ps. Diener et Bs. Bregman, FETAL SPINAL-CORD TRANSPLANTS SUPPORT GROWTH OF SUPRASPINAL AND SEGMENTAL PROJECTIONS AFTER CERVICAL SPINAL-CORD HEMISECTION IN THE NEONATAL RAT, The Journal of neuroscience, 18(2), 1998, pp. 779-793
Cervical spinal cord injury at birth permanently disrupts forelimb fun
ction in goal-directed reaching. Transplants of fetal spinal cord tiss
ue permit the development of skilled forelimb use and associated postu
ral adjustments (Diener and Bregman, 1998, companion article). The aim
of this study was to determine whether transplants of fetal spinal co
rd tissue support the remodeling of supraspinal and segmental pathways
that may underlie recovery of postural reflexes and forelimb movement
s. Although brainstem-spinal and segmental projections to the cervical
spinal cord are present at birth, skilled forelimb reaching has not y
et developed. Three-day-old rats received a cervical spinal cord overh
emisection with or without transplantation of fetal spinal cord tissue
(embryonic day 14); unoperated pups served as normal controls. Neuroa
natomical tracing techniques were used to examine the organization of
CNS pathways that may influence target-directed reaching. In animals w
ith hemisections only, corticospinal, brainstem-spinal, and dorsal roo
t projections within the spinal cord were decreased in number and exte
nt. In contrast, animals receiving hemisections plus transplants exhib
ited growth of these projections throughout the transplant and over lo
ng distances within the host spinal cord caudal to the transplant. Rap
hespinal axons were apposed to numerous propriospinal neurons in contr
ol and transplant animals; these associations were greatly reduced in
the lesion-only animals. These observations suggest that after neonata
l cervical spinal cord injury, embryonic transplants support axonal gr
owth of CNS pathways and specifically supraspinal input to propriospin
al neurons. We suggest that after neonatal spinal injury in the rat, t
he transplant-mediated reestablishment of supraspinal input to spinal
circuitry is the mechanism underlying the development of target-direct
ed reaching and associated postural adjustments.