Muscular Overuse Augments Spinal Cord Cross-over Serotoninergic Fibers during Recovery from Thoracic Spinal Cord Hemisection in Rats

Abstract

Spinal cord cross-over serotoninergic fibers increase when the thoracic spinal cord of a rat is hemisected and the recovery of locomotion is stimulated. The purpose of this study was to examine whether muscular overuse affects this increase in spinal cord cross-over serotoninergic fibers. Forty-four Wister male rats (6 weeks old) were divided into a control group (n=13) and an experimental group (n=31). All rats of the experimental group underwent right thoracic spinal cord hemisection (T8), and 18 of them were recovered with no other procedures. The other 13 rats in the experimental group were further underwent denervation of the contralateral left sciatic nerve to bring about a compensatory overuse on the ipsilateral right hindlimb. The rats were then sacrificed every week for 3 weeks after thoracic spinal cord hemisection. Distribution of the spinal cord cross-over serotoninergic fibers in the lumbosacral ventral horn was examined by immunohistochemical methods, and found to be more prevalent in the hemisected with the denervation of contralateral sciatic nerve than in the other hemisected rats. The results of this experiment suggest that the increase of the spinal cord cross-over serotoninergic fibers following thoracic spinal cord hemisection may be encouraged by overuse of the hindlimb.