TRANSPLANTS ENHANCE LOCOMOTION IN NEONATAL KITTENS WHOSE SPINAL-CORDSARE TRANSECTED - A BEHAVIORAL AND ANATOMICAL STUDY

We have studied the locomotor development of kittens that received com plete low thoracic spinal cord transections and embryonic spinal cord transplants as newborns. Embryonic spinal cord (E21-E26) transplanted into the site of a transection integrated well with the host spinal co rd and promoted the development of overground locomotion. Spinalized k ittens with transplants were first distinguished from spinalized kitte ns during the 2nd and 3rd postnatal weeks when kittens with transplant s positioned their hindlimbs underneath their bodies which promoted su pport of the hindquarters. By postnatal Week 6, kittens with transplan ts exhibited overground locomotion characterized by full weight suppor t and moderate balance control. By 20 weeks of age, as many as 96% of the step cycles showed full weight support and as few as 2% of the ste p cycles were interrupted by a fall. Most kittens also showed coordina tion between the forelimbs and the hindlimbs. They differed hom normal in the precocious onset of reflex stepping and in the less precise in terlimb coordination and more precarious balance during overground loc omotion. The overground locomotor performance of kittens with transpla nts greatly exceeded that of spinal kittens without transplants since few spinalized kittens showed any full-weight-supported step cycles an d none showed coordination between the forelimbs and the hindlimbs. In the absence of a transplant, no fibers could grow across the lesion s ite. In the presence of a transplant, fibers grew across the lesion si te and established anatomical connectivity with the host. Host segment al systems identified by the presence of calcitonin gene-related pepti de- and substance P-immunoreactive fibers were found throughout the tr ansplants. Descending host systems of supraspinal origin were identifi ed by serotonin- and dopamine beta-hydroxylase-immunoreactive fibers t hroughout the transplants. The growth of supraspinal axons into the tr ansplant, and in one ease into the caudal host spinal cord, provided a possible anatomical basis for the development of coordinated overgrou nd locomotion. (C) 1995 Academic Press, Inc.