BACKGROUND AND AIMS: Serotonin, which is supplied to the spinal cord by serotoninergic cells localized in the raphe nuclei and parapiramidal areas of the medulla, plays a very important role in control of the spinal locomotor central pattern generator (CPG). In our previous study we showed that intraperitoneal application of: 8-OH-DPAT (5-HT1A and 5-HT7 serotonin receptor agonist) and quipazine (mainly 5-HT2A serotonin receptor agonist), or intraspinal transplantation of serotonergic cells isolated from 14-day old rat embryo brain stem, facilitates locomotor-like hindlimb movements in spinal rats (spinal cord total transection between Th9 and Th10). 5-HT7 and 5-HT2 serotonin receptor antagonists blocked the locomotor-like hindlimb movements that had been restored in spinal rats grafted with embryonic serotoninergic cells. The aim of the present study was to examine the influence of spinal cord total transection and transplantation of serotonin neurons isolated from the 14-day old rat embryo brain stem on changes in expression of genes encoding 5-HT2A, 5-HT2C and 5-HT7 serotonin receptors in populations of motoneurons innervating tibialis anterior, gastrocnemius lateralis, and extensor caudae medialis muscles. METHODS: For motoneurons labeling a method of retrograde staining using intra muscle injection with cholera toxin B subunit conjugated with Alexa Fluor 555 was used. Motoneurons were then collected by using the laser capture micro-dissection method, and changes in expression of genes encoding serotonin receptors were analyzed by Real-time PCR. RESULTS: The results show that total spinal cord transection changed expression of genes encoding 5-HT2A, 5-HT2C and 5-HT7 serotonin receptors in ankle flexor and ankle and tail extensor muscles. Grafting of serotonin neurons reverses the effects of spinal cord injury on expression of these genes. CONCLUSION: This is the first demonstration that grafts of serotonergic neurons can reverse changes in gene expression in motoneurons produced by spinal cord injury.
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