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Abstract
The purpose of this study was to develop a model of unilateral cervical (C4-C5) spinal
cord contusion injury in the rat and to characterize the functional and histological
consequences following three injury levels using a new weight-drop spinal cord injury
device. We evaluated forepaw/forelimb and hindlimb functions by: (1) a horizontal
ladder beam measuring paw misplacements and slips; and (2) the forelimb preference
test which measures the forelimb used for pushing off to rear, for support, and to
land on after rearing. Rats with a mild spinal cord injury displayed primarily a forepaw
deficit (forepaw misplacements) for 8 weeks after injury. Paw preference also improved
after injury, but failed to reach control levels even after 12 weeks. These rats had
damage primarily to the rubrospinal, spinocervicothalamic, and the uncrossed lateral
corticospinal tracts in the dorsolateral funiculus a well as some loss of the lateral
spinothalamic tracts in the lateral funiculus. Rats with a moderate injury had a prominent
forepaw deficit still evident at 12 weeks after injury as well as a mild but not significant
hindlimb deficit. Paw preference improved slightly 12 weeks. There was a larger lesion
in the dorsolateral and lateral funiculi than in mildly injured rats which extended
into the ventrolateral funiculi. There was a significant loss of gray matter compared
to rats with a mild injury. Rats with a severe injury displayed significant forelimb
and hindlimb deficits throughout the 12 week testing period compared to rats with
a mild or moderate injury, and also had a more severe paw preference bias (90%). The
lesion encompassed the entire dorsolateral, lateral and ventrolateral funiculi with
some disruption of the ventral funiculus. There was more significant gray matter necrosis
compared to rats with either a mild or moderate injury. Thus, the spinal cord injury
device we used may be useful for studying graded cervical spinal cord injury in rats
and potential treatments or interventions, because both the behavioral and histological
effects are reproducible and consistent.