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Abstract

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 — 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.

Item Type:	Thesis - PhD
Authors/Creators:	Fry, Elizabeth Jane
Keywords:	Spinal cord, Opossums, Nervous system
Copyright Holders:	The Author
Copyright Information:	Copyright 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).
Additional Information:	Thesis (Ph.D.)--University of Tasmania, 2002. Includes bibliographical references
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