FETAL TRANSPLANTS ALTER THE DEVELOPMENT OF FUNCTION AFTER SPINAL-CORDTRANSECTION IN NEWBORN RATS

Pieces of fetal spinal tissue were transplanted into the site of compl ete midthoracic spinal transections in neonatal rat pups !transplant r ats). The development of locomotion in these animals was compared with that of unoperated control rats and rats that received spinal transec tions alone (spinal rats). Reflex, treadmill and overground locomotion , staircase descent, and horizontal ladder crossing for a water reward were tested in control, spinal, and transplant rats from 3 weeks to a dulthood. All tests were readily performed by control animals. Most sp inal rats were unable to make many linked weight-supported steps on th ese tasks. Transplant rats were variable in their locomotor capabiliti es, but a subset of rats were able to demonstrate coordinated and adap table locomotion on these tasks. Some transplant rats performed better on more challenging tasks, suggesting that motor strategies for these tasks used different information, perhaps from descending systems. Tr ansplanted tissue survived, and in most cases there was immunocytochem ical staining of serotonergic fibers passing into and caudal to the tr ansplant, supporting the conclusion that descending systems grew throu gh the transplanted tissue. Integration with the host tissue was often poor, suggesting that nonspecific or trophic effects of the transplan t might also contribute to the development of locomotor function. Ther efore several mechanisms may contribute to the repair of injured spina l cord provided by transplants that permit the development of useful l ocomotion.