Forelimb motor performance following cervical spinal cord contusion injury in the rat

The purpose of this study was to examine the degree, persistence, and nature of forelimb behavioral deficits following cervical spinal cord contusion injury in the rat. Forelimb reaching and pellet retrieval, forehead adhesive sticker removal, and vibrissae-induced forelimb placing were examined for 16 weeks following a weight-drop injury (10.0 g-2.5 cm) at the C4-C5 spinal level. Nine of 13 rats studied were unable to perform the pellet retrieval task due to pronounced forelimb extension hypometria. However, these animals did carry out the forehead sticker removal and vibrissae-induced placing tasks. Therefore, the loss of reaching ability related to pellet retrieval was not due to generalized paralysis. This interpretation was further supported by evaluation of the rostrocaudal extent of relative motoneuron loss from 1-mm divisions through the lesion zone. The extent of motoneuron pathology ranged from 2 to 6 mm but was largely confined to the C4-C5 spinal segments. Morphometric assessments of axonal sparing revealed that pellet retrieval performance during the last month of observation was significantly correlated with fiber sparing in the dorsal columns and ventral white matter, whereas no significant correlation could be demonstrated with regard to dorsolateral white matter. While there were no conspicuous differences in qualitative assessments of damage to interneuron pools (i.e., laminae V to VII) between the nonreaching and retrieval-recovered rats, the possibility of combined white and gray matter pathology contributing to this deficit still exists. These initial findings thus demonstrate that the weight-drop contusion injury model can be adopted to studies of cervical spinal cord trauma in the rat. Such lesions yield permanent deficits in forelimb function lending to future studies of possible therapeutic interventions. Furthermore, performance deficits observed at 1 week postinjury in the placing and forehead sticker removal tasks can be predictive of any potential for long-range spontaneous recovery in pellet retrieval ability.