Abstract
The objective of this study was to electrophysiologically assess the corticospinal tracts of adult rats and the recovery of motor function of their forelimbs after cervical cord hemisection. Of 39 adult rats used, compound muscle action potentials (CMAPs) of the forelimbs of 15 rats were evaluated, before they received left C5 segmental hemisection of the spinal cord, by stimulating the pyramid of the medulla oblongata on one side using an exciting microelectrode. All 15 rats exhibited contralateral electrical activity, but their CMAPs disappeared after hemisection. The remaining 24 rats received hemisection first, and CMAPs of 12 rats were assessed over time to study their recovery time. All of them exhibited electrical activity of the forelimbs in 4 weeks after surgery. The remaining 12 rats received additional right C2 segmental hemisection, and variation of CMAPs between before and after surgery was examined. The right side of the 12 rats that received the additional hemisection exhibited no electrical activity in response to the stimulation of the pyramids on both sides. These results suggest that changes in path between the resected and healthy sides, activation of the ventral corticospinal tracts, and propriospinal neurons were involved in the recovery of motor function after cervical cord injury.
Highlights
It is considered that a damaged central nervous system will never be restored [1], but we reported that the once paralyzed motor function of the forelimbs of juvenile rats had been restored due to a significant change that occurred in the corticospinal tract pathways after a brain injury [2]
We assessed the motor function of the forelimbs of these rats following cervical cord hemisection and reported that restoration of motor function was observed in approximately 60% of the juvenile rats and 40% of the adult rats [3]
It has been confirmed using adult rats that unilateral damage in the cerebral hemisphere caused during the juvenile period allows the corticofugal projection fibers that are descending from the sensorimotor area of the cerebral cortex on the undamaged side to form bilateral axonal projections at each level of the thalamus [14]; striatum [15]; superior colliculus, red nuclei, and pontine nuclei in the midbrain [16]; pyramidal decussation [17]; and spinal cord [18]
Summary
It is considered that a damaged central nervous system will never be restored [1], but we reported that the once paralyzed motor function of the forelimbs of juvenile rats had been restored due to a significant change that occurred in the corticospinal tract pathways after a brain injury [2]. In past anatomical verification of experiments in corticospinal tract injury of rodents, it was reported that axonal re-elongation and collateral sprouting occurred in the damaged part and the axons of intact neurons extended new branches in an area apart from the damage, allowing the hind limbs to recover better than the forelimbs [4,5,6]. This recovery process has never been electrophysiologically verified over time. The objective of this research was to electrophysiologically assess the corticospinal tract of adult rats, electrophysiologically verify the recovery of the forelimb motor function over time after cervical cord hemisection, and lastly, examine the compensation pathways for the recovery of motor function by conducting an additional hemisection
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