Effects of Spinal Cord Injury on Motor Skill Learning, Brain Rhythms and Dopamine Levels in the Primary Motor Cortex of Rats

Abstract

The loss of spinal sensorimotor pathways following spinal cord injury (SCI) can induce retrograde neurodegeneration in the brain, especially the primary sensorimotor cortex. Whereas increased rate of spontaneous single-neuron activity in the hindlimb and forelimb areas (HLA, FLA) of the rat primary motor cortex (M1) after thoracic SCI has been reported, we aimed to examine the effects of a thoracic SCI model on remote oscillatory activity, biochemical changes and motor skills learning. Methods: Twenty-four male Wistar rats were randomly subjected to control, laminectomy or contusion SCI at the thoracic (T10) level. Oscillatory activity and motor skills performance were evaluated for six consecutive days using local field potential (LFP) recording and skilled forelimb reaching task, respectively. Dopamine (DA) levels and expression of dopamine receptors (D1 and D2) were determined in HLA and FLA by ELISA and Western blotting, respectively. Results: The electrophysiological results (HLA in rest and FLA in rest or task condition) showed a sustained increase of LFP power in SCI rats compared with uninjured rats. SCI rats had a lower performance and learning rate in the skilled forelimb reaching task in contrast to uninjured rats. Biochemical analysis of HLA and FLA showed reductions in DA levels and expression of D1R and D2R after SCI