Comparing deficits following excitotoxic and contusion injuries in the thoracic and lumbar spinal cord of the adult rat

The majority of human spinal cord injuries involve gray matter loss from th e cervical or lumbar enlargements. However, the deficits that arise from gr ay matter damage are largely masked by the severe deficits due to associate d white matter damage. We have developed a model to examine gray matter-spe cific deficits and therapeutic strategies that uses intraspinal injections of the excitotoxin kainic acid into the T9 and L2 regions of the spinal cor d. The resulting deficits have been compared to those from standard contusi on injuries at the same levels. Injuries were assessed histologically and f unctional deficits were determined using the Basso, Beattie, and Bresnahan (BBB) 21-point open field locomotor scale and transcranial magnetic motor e voked potentials (tcMMEPs). Kainic acid injections into T9 resulted in subs tantial gray matter damage; however, BBB scores and tcMMEP response latenci es were not different from those of controls. In contrast, kainic acid inje ctions into L2 resulted in paraplegia with BBB scores similar to those foll owing contusion injuries at either T9 or L2, without affecting tcMMEP respo nse latencies. These observations demonstrate that gray matter loss can res ult in significant functional deficits, including paraplegia, in the absenc e of a disruption of major descending pathways. (C) 1999 Academic Press.