Changes Of 5-HT Receptor Subtype MRNAs Expression In Rat Dorsal Root Ganglia And Spinal Dorsal Horn Induced By Neuropathic Pain

Serotonin (5-hydroxytryptamine, 5-HT) is an important neurotransmitter and has been implicated in numerous functions, such as modulation of locomotion, nociception, feeding behaviour, regulation of body temperature, anxiety and depression. 5-HT plays its effects through binding to a variety of its membrane-bound receptors. 5-HT and its receptors are found both in the central and peripheral nervous system (CNS/PNS). Recent years with the development of molecular biology 14 kinds of 5-HT receptor subtypes have been cloned, which can be subdivided into seven subfamilies. With the exception of the 5-HT3 receptor subtype which is a ligand-gated ion channel, all other 5-HT receptors belong to the G-protein-coupled receptors. It is believed that 5-HT is involved in analgesia in the central nervous system and in facilitation of the nociceptive transmission in the periphery. Because of the lack of specific antibody, agonist and antagonist for 5-HT receptor subtypes, the exact role of each 5-HT receptor subtypes in mediating 5-HT-induced modulation of nociception at spinal cord or peripheral level remain unclear.Neuropathic pain is a familiar sight of many patients and it can be suffering. Discussing the mechanism of neuropathic pain could not only relieve the suffering of patient but also improve their quality of life. At present, the functions of 5-HT involved in neuropathic pain are not clear. We observed the different changes of 5-HT receptor subtypes mRNAs in neuropathic pain to learn the roles of 5-HT. Because the kinds of 5-HT receptor is miscellaneous, so studies should be done to clarify which receptor subtypes are related with neuropathic pain.In the present study, the changes of 5-HT receptor subtypes mRNAs in the spinal dorsal horn and DRG induced by spared nerve injury (SNI) on the branches of the sciatic nerve in the rat were detected by using reverse transcriptase polymerase chain reaction (RT-PCR) method. 1. Changes of 5-HT receptor subtypes mRNAs in DRG of rat induced by SNI5-HT₁A, 5-HT₁B, 5-HT₁D, 5-HT₁F, 5-HT₂A, 5-HT₃, 5-HT₄, 5-HT₅A and 5-HT7 receptor subtypes mRNAs were detected in the DRG of the rat by using RT-PCR. However the expression of 5-HT₁E, 5-HT₂B, 5-HT₂C, 5-HT₅B and 5-HT₆ receptor subtypes mRNAs were not observed in DRG.RT-PCR revealed that after SNI, the mRNA expressions of 5-HT₁A, 5-HT₁b, 5-HT₁f, 5-HT₂A, 5-HT₃, 5-HT₄ and 5-HT₇ receptor subtypes within the ipsilateral lumbar DRG increased significantly. No such changes were observed on the expression of 5-HT₁d and 5-HT₅a receptor subtyopes mRNAs. There were no remarkable changes of the expression of mRNA encoding for each subtype of 5-HT within the contralateral DRG. The present results suggest that different 5-HT receptor subtypes might play different roles in SNI-induced neuropathic pain at the prepheral level.