Rapid functional recovery after spinal cord injury in young rats.

Responses to traumatic injury in the immature spinal cord may be different from those in adults. We modified an adult model of weight-drop injury to characterize the histopathology and functional recovery after spinal cord injury (SCI) in rat pups at postnatal day 14-15. A 10-g weight was dropped from 2.5 or 5.0 cm at T8-T9. Hindlimb function was evaluated at 24 h and 1, 2, 3, and 4 weeks after injury using the Combined Behavioral Score that estimates overall hind limb sensorimotor function, and the BBB scale for open field locomotion. Histopathology was examined at 15 min, 24 h, and 4 weeks after SCI. The initial hemorrhagic lesion was similar to that seen in adults, but the time course of secondary loss of ventral horn motor neurons was extended. By 4 weeks, only a partial rim of white matter surrounding a central cavity was seen. The 5.0 cm injury group exhibited significantly less recovery of function at 4 weeks than the 2.5 cm group. In the latter, the degree of hindlimb deficit at 4 weeks was similar to that previously described for adults with 10 g x 2.5 cm SCI. However, pups in both injury groups exhibited a significantly faster rate of recovery than adults. Recovery was maximal by 1 week after SCI in pups as compared to 3-4 weeks in adults. The more rapid functional recovery observed in the pups suggests that this new model may be useful for studying mechanisms of functional plasticity after SCI.