Growth of myelinated lumbosacral ventral root fibers in kittens after early postnatal dorsal rhizotomy, dorsal rhizotomy and spinal cord hemisection, or sciatic neurectomy

Abstract

The fiber-size distribution of myelinated lumbosacral ventral root fibers was studied in 14 kittens at various survival times after unilateral transection of corresponding dorsal roots at 8 days of age. In six animals an ipsilateral spinal cord hemisection was made in addition to dorsal rhizotomy. For comparison, two kittens were subjected instead to a unilateral sciatic neurectomy. The size spectra obtained from the ventral roots on the side of the lesion were compared with the fiber-size distribution in the same roots on the side not affected by the operation. In addition, three normal kittens were used as control animals. The findings show that neither the dorsal rhizotomy nor the combined dorsal rhizotomy and spinal cord hemisection had any measurable effect on the postnatal growth of the myelinated fibers in the relevant roots. The lesions resulted in a grave motor deficit which suggests that a normal function is not of any major importance for the growth in fiber size. After sciatic neurectomy the size spectrum of the myelinated fibers in ventral roots L7 and S1 showed a distinct shift to the left indicating a more severe retrograde degeneration of large than of small ventral horn neurons.