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and not to native spinal cord circuitry, the function is expected
to be lost when after a retransection of the cord is established.
3.
Incomplete Transection
: In incomplete transection models,
tracts of the spinal cord are cut selectively. Since neurologic
deficit can be relatively mild, the postoperative animal care is
easy, especially with regard to bladder function. Thus, com-
parison of the regeneration in a particular tract with its heathy
partner on the contralateral hemicord is possible. Retrograde
tracers are available to confirm the lack of any axon escaping
from the induced injury of a particular tract. To which degree
an observed functional improvement is due to true regenera-
tion of the injured tract or to functional compensation from
other systems that are spared is still waiting to be explored.
Unilateral or dorsal hemisection models are commonly used to
transect the ipsilateral rubrospinal tract or bilateral rubrospinal
plus corticospinal tracts, respectively.
4. Blunt contusive or compressive force to the spinal cord, which
is more representative of what occurs in most human injuries
(
5, 25-28
) leads to a temporal pattern of injury maturation
resulting with central cystic cavities in an athrophic cord and
gliosis. Such blunt trauma leaves some normal-appearing
parenchyma peripherally at the injury core and preserved func-
tion is related with the quantity of this spared rim. Due to the
incomplete nature of injury as well as the complexity of the tracts
and the existing discrepancies between the conditions (such as
an anesthesia, or multiple drug use) under which injuries occur
in patients and those in animals, much effort should be directed
at optimizing the selected experimental method in order to
induce reproducible and consistent neurologic injuries.
5.
New York University Impactor
: This model can induce consis-
tent injuries in terms of the resulting neuropathology as well as
the functional impairment as evaluated on the BBB scale. The
average BBB scores from these four groups 6 weeks after injury
were 19.0 ± 15.8, 11.4 ± 1.1, 10.6 ± 0.6, and 7.9 ± 1.8, respec-
tively, whereas animals with full transections achieved a score of
3.3 ± 2.1. It should be noted that even in the most severe injury,
caused by weight dropped from a height of
50
mm, the animals'
functional recovery nearly reaches some degree of hindlimb
weight support. There is an interaction between the kinetic
energy of the descending impactor, its mass and its velocity at
impact. The relation is linear between energy and drop height
and nonlinear between impact velocity and drop height. In the
attempt to compare results obtained in other weight-drop
devices, it is important to be aware of the biomechanical impli-
cations of differences in drop height, impact mass, or both.
6.
Ohio State University Impactor
: While both the OSU and NYU
impactors were developed for the rat, the Ohio State group
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