Functional involvement of the lumbar spinal cord after contusion to T8 spinal segment of the rat

Abstract

To evaluate the effects on locomotion and lumbar motoneuron function after a contusion to the midthoracic spinal cord of the rat. Five animals received a moderate contusion on T8, and over 28 days postoperation (dpo) locomotion and motor electrophysiological outcome were compared with five sham-operated animals. At 28 dpo, the contused animals supported their body weight (BBB score =11.5 ± 0.5) and stepped uncoordinatedly. Motor evoked potentials recorded in the tibialis anterior (TA) and plantar muscles (PL), and longitudinal interlimb reflexes recorded in the TA muscles were abolished. The M wave recorded in the TA showed a decrease in amplitude by 7 dpo, which remained invariable until the end of the evaluation (88 ± 3% of {preoperative} values), whereas in the PL muscle it was not affected. Injured animals presented hyperreflexia, as shown by an increased H/M ratio. Histological analysis showed similar number of retrogradely traced TA motoneurons between groups, and that contused animals presented hypertrophied astrocytes in the most rostral but not caudal segments of the lumbar enlargement. These results indicate that after contusion to the thoracic spinal cord, the lumbar segments undergo structural and functional changes, following a rostro-caudal gradient extension.