Behavioral and histological characterization of unilateral cervical spinal cord contusion injury in rats

Most experimental studies of spinal cord injury (SCI) in rats damage the thoracic cord, with the consequent functional loss being due to interruption of long tracts connecting the caudal spinal cord to the rostral nervous system. Less work has been done evaluating injury to the cervical cord, even though it is the most common level of human SCI. In addition to the long tracts, the cervical spinal cord contains the sensory and motor neurons responsible for upper extremity function. The purpose of this study was to further develop a rat model of cervical spinal cord contusion injury using a modified NYU/MASCIS weight drop device. Mild (6.25 mm) and moderate (12.5 mm) C5 unilateral injuries were produced. Behavioral recovery was examined using a grooming test, a paw preference test, a walkway test (The Catwalk), and a horizontal ladder test. Histological outcome measures included sparing at the lesion epicenter, sparing throughout the extent of the lesion, quantification of myelin loss rostral and caudal to the lesion, and motor neuron counts. Compared to controls, animals receiving SCI exhibited injury severity-specific deficits in forelimb, locomotor, and hindlimb function persisting for 6-weeks post-SCI. Histological analysis revealed ipsilateral containment of the injury, and differentiation between groups on all measures except motor neuron counts. This model has many advantages: (1) minimal animal care requirements post-SCI, (2) within subject controls, (3) functional loss involves primarily the ipsilateral forelimb, and (4) it is a behavioral and histological model for both gray and white matter damage caused by contusive SCI.