Distribution Of 5-HT₁ Receptor Subtypes In The Spinal Cord And Dorsal Root Ganglion In The Rat And Changes Of Them Induced By Bee Venom Injection

Serotonin (5-hydroxytryptamine, 5-HT) is an important neurotransmitter and has been implicated in numerous functions, including modulation of locomotion, nociception, feeding behaviour, regulation of body temperature and psychiatric disorders, such as anxiety and depression. 5-HT exerts 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), as well as in a number of non-neuronal tissues, such as in the gut and cardiovascular system. Over the past 10 years, molecular cloning has revealed the presence of 14 kinds of 5-HT receptor subtypes, which can be subdivided in seven subfamilies. With the exception of the 5-HT3 receptor, which is a ligand-gated ion channel, all other 5-HT receptors belong to the G-protein-coupled receptor. 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 distribution of 5-HT receptor subtypes in the spinal cord and DRG in addition to the functions they mediate in the transmission and modulation of nociception remain unclear.In the present study, expressions of 5-HT1 receptor subtype mRNAs in the spinal dorsal and ventral horns at different segments. DRG and their changes under BV-induced inflammatory condition in the rat was detected by using reverse transcriptase polymerase chain reaction (RT-PCR) method.1. Expressions of 5-HTi receptor subtype mRNAs in the spinal dorsal and ventral horns at different segments in the rat and changes of them induced by bee venom injection5-HT1A, 5-HT1B, 5-HT1D and 5-HT1F receptor subtype mRNAs were detected in the spinal cord of the rat by using RT-PCR. The relative gray levels of the bands, expressed as optical density units, were quantitatively analyzed using Labworks image software. Results from the RT-PCR experiments revealed that 5-HTiA, 5-HT1B and 5-HT1D receptor subtype mRNAs presented at higher expression level in the dorsal horn and at lower expression level in the ventral horn at the thoracic, lumbar and sacral segments of the spinal cord. For the cervical cord, the expression levels of the 5-HT1A, 5-HT1B and 5-HT1D receptor subtype mRNAs in the dorsal horn were slightly higher than that in the ventral horn. 5-HT1E receptor subtype mRNA was not detected in the spinal cord. 5-HT1F receptor subtype mRNA was found at high expression level in both dorsal and ventral horns at all segments.Subcutaneous injection of BV into the hindpaw of the rat has been used experimentally to produce not only spontaneous pain but also hyperalgesia inconscious rats and can serve as a good model for clinical pathological pain. Behavioral studies have shown that BV injection causes a persistent spontaneous pain for 1 h followed by a long-term period of hyperalgesia which peaks at 2-4 h after BV injection. Expressions of 5-HT1 receptor subtype mRNAs in the spinal cord at L₃-L₆ segments were observed by using RT-PCR after 1 h and 4 h of the BV administration. On the right half of the spinal cord, ipsilateral to the BV injection, expressions of HT1A and 5-HT1B receptor subtype mRNAs increased significantly at both 1 h and 4 h. On the left half of the spinal cord, contralateral to the BV injection, expressions of S-HT1A and 5-HT1B receptor subtype mRNAs remained no markable changes. No significant changes were observed for the expression of 5-HT1D and 5-HT1F receptor subtype mRNAs both on the contralateral and ipsilateral sides of the spinal cord. 5-HT1E receptor subtype mRNA in the spinal cord was still not detected even under BV stimulation.2. Expressions of 5-HT| receptor subtype mRNAs in rat DRG and changes of them induced by bee venom injectionRT-PCR showed that 5-HT1A, 5-HT1B, 5-HT!D and 5-HT1F receptor subtype mRNAs were present in the DRGs. The relative gray levels of the bands, expressed as optical density units, were...