Sprouting of primary afferent fibers after spinal cord transection in the rat
Section snippets
Spinal cord transection
All protocols for these experiments were approved by the University of Western Ontario Animal Care Committee in accordance with the policies established in the Guide to Care and Use of Experimental Animals prepared by the Canadian Council on Animal Care. Twenty-six male Wistar rats (Charles River), weighing 300–400 g, were premedicated with atropine (1 mg/kg, i.p.) and diazepam (2.5 mg/kg, i.p.). After 10 min, these rats were anesthetized with 35 mg/kg sodium pentobarbital (i.p.), and supplemental
Cholera toxin subunit B immunoreactivity
In control rats, CTB-IR in myelinated fibers was found in individual fibers and in a punctate form associated with terminals. This CTB-IR was found in segments T6–T9, corresponding to the intercostal muscle injection, and in segments L1–L7, transported from the quadriceps muscle injection site. CTB-IR was found throughout laminae I–V in T6–T9 and L1–L7, and in Clarke's nucleus in the lumbar segments (Fig. 2A, D). No CTB-IR fibers could be seen extending into the ventral or lateral horn anywhere
Discussion
Both myelinated and unmyelinated primary afferent neurons sprouted, but the changes in each group occurred in different spinal cord segments and followed a different time-course after the injury. The area of myelinated afferent fibers, labeled with CTB, increased in the dorsal horn of lumbar spinal cord segments by one week after SCT and this change persisted for two weeks, while no changes were seen in the thoracic cord. In contrast, the unmyelinated afferent fibers, identified by their
Conclusions
These experiments have demonstrated sprouting of both myelinated and unmyelinated primary afferent fibers after spinal cord injury. As each afferent population sprouts at a different time after transection, each may be responding to a different cue within the injured cord. Although no direct projections were observed into the lateral or ventral horns, the putative new neurites may provide excitatory inputs to interneurons antecedent to SPNs or motor neurons. Thus, primary afferent sprouting may
Acknowledgements
This research was supported by grant no. T2679 from the Heart and Stroke Foundation of Ontario and a grant from the Medical Research Council of Canada. L. C. Weaver is the recipient of a Career Investigator award from the Heart and Stroke Foundation of Ontario, and N. R. Krenz holds a studentship from the Medical Research Council of Canada. The authors are grateful to M. Korkola for carrying out pilot studies, S. Hota, C. Nutt and M. Columbus for technical assistance, and B. Atkinson for
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