FETAL SPINAL-CORD TRANSPLANTS SUPPORT THE DEVELOPMENT OF TARGET REACHING AND COORDINATED POSTURAL ADJUSTMENTS AFTER NEONATAL CERVICAL SPINAL-CORD INJURY

Neonatal midthoracic spinal cord injury disrupts the development of po stural reflexes and hindlimb locomotion. The recovery of rhythmical al ternating movements, such as locomotion, is enhanced in injured animal s receiving fetal spinal cord transplants. Neonatal cervical spinal co rd injury disrupts not only locomotion but also skilled forelimb movem ent. The aims of this study were to determine the consequences of cerv ical spinal cord injury on forelimb motor function and to determine wh ether transplants of fetal spinal cord support normal development of s killed forelimb use after this injury. Three-day-old rats received a c ervical spinal cord lesion at C3, with or without a transplant of feta l cervical spinal cord (embryonic day 14); unoperated pups served as c ontrols. Animals were examined daily during the first month of life us ing a behavioral protocol that assessed reflexes, postural reactions, and forelimb motor skills. They also were trained and tested as adults to assess performance in goal-directed reaching tasks. The onset of p ostural reflexes was delayed in the lesion-only group, and goal-direct ed reaching and associated postural adjustments failed to develop. The transplant group developed reflex responses and skilled forelimb acti vity that resembled normal movement patterns. Transplant animals devel oped both target reaching and accompanying postural adjustments. Targe t reaching requires integration of segmental, intersegmental, and supr aspinal input to propriospinal and motor neurons over many spinal cord levels. Transplants may support the reestablishment of input onto the se neurons, permitting the development of skilled forelimb activity af ter neonatal cervical spinal cord injury. The neuroanatomical reorgani zation of descending and propriospinal input was examined in the compa nion paper (Diener and Bregman, 1998).