Fig. 8. Retrograde labeling of propriospinal neurons. A, In normal animals at P3, propriospinal neurons (arrows) labeled with Fast Blue are distributed throughout laminae VII–VIII and X. This indicates that at the time of the neonatal spinal cord injury, at least some of the propriospinal neurons are axotomized directly. B, Schematic diagram representing the general distribution of the propriospinal neurons (represented as stars in LSN, laminae IV–VI, VII–VIII, and X) in the brachial cord of a normal adult rat. C, HX group, spinal cord segment caudal to the injury site. Compared with the normal distribution of propriospinal neurons in adult rats (data not shown), there is a decrease in the number of propriospinal neurons after neonatal hemisection (C). The decrease in labeling is greatest on the side ipsilateral to the lesion but is evident bilaterally. D, HX + TP group, spinal cord segment caudal to the lesion plus transplant. In contrast to lesion-only animals, animals with transplants had many retrogradely labeled propriospinal neurons present bilaterally. These neurons were located in all of the appropriate laminae (IV–VIII, X, and LSN). Thus, the transplants rescue a substantial proportion of the propriospinal neurons. Scale bars, 50 μm. LSN, Lateral spinal nucleus; CC, central canal.