Influence of spinal cord hemisection on the configurational changes in motor and primary afferent neurons and the chemical messenger alterations in the rat lumbar segments.

Cholera toxin B subunit (CTB), a retrograde transport marker, was injected into the rat gastrocnemius muscles, and changes in CTB-labeling pattern of motoneurons and primary afferent neurons at the level L4 and L5 after spinal cord hemisection of the L1 level were observed in conjunction with the alterations of chemical messengers such as serotonin (5-HT), calcitonin gene-related peptide (CGRP), substance P (SP), galanin (Gal), Met-enkephalin (Enk), and neuropeptide Y (NPY). Motoneurons at the L4 and L5 levels on the lesioned side exhibited significant shrinkage of their dendritic arbors without apparent loss of their number throughout all stages from 1 to 12 weeks after the hemisection of the spinal cord. Postoperatively, central processes of neuron of the dorsal root ganglia (DRG) on the lesioned side increased progressively compared to that on the contralateral side with the passage of time. The percentage of CTB-labeled neurons in the DRG has been consistently smaller in number on the lesioned side after the operation, and the difference between sides became more apparent during the later postoperative stages. 5-HT-containing fibers in the anterior and posterior horns on the lesioned side showed a significant decrease in the number, while no apparent changes were observed in the distribution of nerve fibers containing CGRP, SP, Gal, Enk, and NPY.