whole_FryElizabethJane2002_thesis.pdf (25.89 MB)
Regeneration of supraspinal projections after spinal cord injury in the neonatal opossum, Monodelphis domestica
thesisposted on 2023-05-26, 20:22 authored by Fry, Elizabeth Jane
The studies presented in this thesis define the developmental sequence of descending supraspinal projections in both control and spinally transected neonatal opossums using an axonal tracer (dextran amine) injected into the lumbar spinal cord at post-natal day (P) 7, P14, P21, P28, P35 and adulthood. All experiments were conducted in accordance with NHMRC guidelines and with the approval of the University of Tasmania Ethics (Animal) Committee. The numbers of retrogradely labelled neuronal cell bodies (indicating projections traced by the dye from the site of injection) were counted in brain sections from animals removed 4 days after injections. The time course of supraspinal projections reappearing across a complete mid thoracic spinal transection made at P7 was then compared to the normal developmental sequence after identical spinal injections in control animals. Supraspinal projections were found to traverse the injury site within one week of the operation and contributed in increasing numbers to lumbar projections across the lesion for up to 4 weeks post-lesion. Numbers of labelled neurons in adults were found to be much lower both for transected and uninjured, control animals. The distribution of neurons in different brain nuclei was similar to that of unlesioned control animals, thus projections appeared to emulate the normal sequence of development after transection. However, there were fewer projections to the lumbar spinal cord after a transection, as compared to control animals, indicating that while many axons were able to grow through an injury site, not all may persist until adulthood. A double-labelled paradigm was employed to determine whether any fibres growing across the injury site were regenerated from axons severed by the transection. Lumbar spinal injections of dextran amine - Oregon green, made at P4, identified a population of supraspinal projections that were severed at P7 by a thoracic spinal transection. A different dextran amine ‚ÄövÑvÆ rhodamine was injected caudal to the lesion site at P7, P14, P21, P28 and P35 to label fibres growing across the lesion site. Neuronal cell bodies found containing both dyes indicated pre-lesion labelled axons that were able to regenerate their severed processes back across the injury site to encounter the second dye. Regenerating fibres increased from approximately 2 % of axons labelled with the first dye at P14, up to approximately 30 % at P35. It appears that regeneration of severed axons does occur following neonatal spinal injury at least in the first 4 weeks post injury.
Rights statementCopyright 2002 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s). Thesis (Ph.D.)--University of Tasmania, 2002. Includes bibliographical references