| Antinociceptive Effects of Intrathecal 5-Hydroxytryptamine and Its Subtype Agonists in the Formalin Test. |
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Myung Ha Yoon, Yeo Ok Kim, Seong Wook Jeong |
1Department of Anesthesiology and Pain Medicine, Medical School, Chonnam National University, Gwangju, Korea. mhyoon@chonnam.ac.kr
2Department of Brainscience, Chonnam National University, Gwangju, Korea. |
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| Abstract |
BACKGROUND
Although 5-hydroxytryptamine (5-HT) is involved in the modulation of nociceptive transmission in the spinal cord, the effect of it is not clear. Previous studies have revealed the presence of many types of 5-HT receptors in the spinal cord. The aim of this study was to determine the role of spinal serotonergic receptors by examination of the effects of intrathecal 5-HT and its subtype agonists on the stimulus evoked by formalin injection.
METHODS
Rats were implanted with lumbar intrathecal catheters. Intrathecal 5-HT and its subtype agonists were administered 10 min before the formalin injection. After the formalin injection, a formalin-induced nociceptive behavior (flinching response) was observed for 60 min.
RESULTS
Intrathecal administration of 5-HT, 5-HT(1A) agonist (dipropyl-5CT), 5-HT(1B) agonist (CGS- 12066A), 5-HT(2) agonist (alpha-methyl-5-HT), 5-HT(2B) agonist (BW723C86), 5-HT(2C) agonist (MK 212), 5-HT(3) agonist (m-CPBG) and 5-HT(4) agonist (BZTZ) produced a dose-dependent suppression of flinches in both phases.
However, neither 5-HT(1D) agonist (GR 46611) nor 5-HT(1E),F agonist (BRL 54443) reduced the flinches in either phase.
CONCLUSIONS
Spinal 5-HT(1A), 5-HT(1B), 5-HT(2), 5-HT(2B), 5-HT(2C), 5-HT(3) and 5-HT(4) receptors may be involved in the regulation of a nociceptive state evoked by a formalin stimulus, whereas spinal 5-HT(1D), 5-HT(1E) and 5-HT(1F) receptors may not be involved. |
| Key Words:
Antinociception; formalin test; 5-HT and its subtype agonists; serotonergic receptors; spinal cord |
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