| 5-l-Iydroxytrytamine (5-HT) is an important neurotransmitter with various functions. 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. These effects of 5-HT might be mediated by mutiple 5-HT receptor subtypes. Till now, 14 subtypes of 7 kinds 5-HT receptor have been cloned. Because of the lack of specific antibody, agonist and antagonist for each subtype, the distributio of 5-HT receptor subtypes and the functions they mediate in the peripheral nociception remain unclear. Dorsal root ganglion (DRG) and trigeminal ganglion (TG) are sensory ganglia. Their central terminals project to the superficial layers of spinal dorsa] horn and caudal subnucleus of the spinal trigeminal nucleus, respectively, and their peripheral terminals terminate in the peripheral tissues. The distribution of 5.HT receptor subtypes in the terminals culd be indirectly deduced according to their distribution in these ganglionic neurons. 5-I-IT has been reported to be involved in activation and sensitization of nociceptors to pathological stimuli, but it remains to be elucidated which subtypes of 5-HT receptor are involved in these effects. It is generally believed that peripheral inflammation causes dramatic changes, including changes of the expression of the peptides and their receptors, in the phenotype of DRG neurons. Such changes might indicate the possible involvement of these peptides and their receptors in nociception. However, little attention has been paid to the changes of peripheral 5-HT receptors located on the primary sensory neurons following long-lasting flow of nociceptive inputs through these neurons. In the present study, reverse transcriptase polymerase chain reaction (RT-PCR) and in situ hybridization methods were used to detect 5-HT receptor subtypes mRNA in rat DRG and TO. Expression changes of 5-HT receptor subtype mRNAs in DRG after injection of complete Freund adjuvant (CFA) into the hindpaw of rats were also determined by RT-PCR method. 1. Distribution of 5-HT receptor subtypes in rat DRG and TG RT-PCR showed that 5-HTIA~ 5-HT19~ 5-HTIDS 5-HT2AS 5-HT3~ 5-HT4 and 5-HT7 receptor subtypes were present in the DRG. TO displayed bands identical to that of the DRG. Positive band intensities for the various 5-HT receptor subtypes were different in DRG and TG. In the DRG, prominent bands were present for the 5-HTID and 5-HT3 receptor subtypes and slightly less prominent bands were present for the 5-HT,B.. 5-HT2AS 5-HT4~ 5-HTIA and 5-HT7 receptors subtypes. In the TO, prominent bands were present for the 5-HT3 and 5-HT,D receptor subtypes and slightly less prominent bands were present for the 5-HTIA~ 5-HT4. 5-HT7~ 5-HT2A and 5-HTIB receptor subtypes. By In situ hybridization method, 5-HTIA. 5-HTIBs 5-HTID~ 5-HT2A~ 5-HT3.~ 5-HT4 and S-HT7 receptor subtype mRNAs positive neurons were observed in both DRG and TO. These results were identical to that of RT-PCR. The number of the positive neurons of the same receptor subtype in the two different ganglia was different. In addition, in the same ganglion, the number of the positive neurons of each subtype was also different. Most of the S-HT receptor subtype positive neurons were medium (26?5 I.im) and small (~25 jim) in diameter. 2. Expression changes of 5-HI receptors in DRG under inflammatory condition The CFA injecton caused inflammatory response with edema in all injected paws, and responses peaked at the fou... |
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