| Evaluation of the Role of 5-Hydroxytryptamine Receptor Subtypes in the Regulation of Nociceptive Transmission in the Rat Spinal Cord. |
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Chang Young Jeong, Hong Buem Bae, Hun Chang Park, Jeong Il Choi, Myung Ha Yoon |
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Department of Anesthesiology and Pain Medicine, Medical School, Chonnam National University, Gwangju, Korea. mhyoon@chonnam.ac.kr |
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| Abstract |
BACKGROUND
Spinal 5-hydroxytryptamine (5-HT) has been shown to display an antinociceptive effect, which is mediated by 5-HT receptors. Previous studies have revealed the presence of at least four types of 5-HT receptors in the spinal cord.
The aim of this study was to assess the role of each spinal 5-HT receptor in the antinociception of intrathecal 5-HT using the formalin test.
METHODS
Rats were implanted with lumbar intrathecal catheters. After the administration of 5-HT, formalin-induced nociceptive behavior (flinching response) was observed for 60 min. To further clarify the role of the 5-HT receptors in the antinociception of 5-HT, several antagonists of 5-HT receptors were administered intrathecally 10 min before 5-HT delivery, and formalin was injected 10 min later.
RESULTS
Intrathecal 5-HT dose-dependently suppressed flinching during phase 1 and 2 in the formalin test. 5-HT1B (GR 55562), 5-HT2C (N-desmethylclozapine), 5-HT3 (LY-278,584) and 5-HT4 (SDZ-205,557) receptors antagonists reversed this antinociception by 5-HT during both phases in the formalin test. 5-HT1A receptor antagonist (WAY-100635) decreased antinociception by 5-HT in phase 2, but not in phase 1. A 5-HT1D receptor antagonist (BRL 15572) did not antagonize the antinociception of 5-HT in either phases.
CONCLUSIONS
Spinal 5-HT1B, 5-HT2C, 5-HT3 and 5-HT4 receptors, but not the 5-HT1D receptor, are involved in the antinociception of serotonin in the facilitated state and in the acute pain evoked by a formalin stimulus. The 5-HT1A receptor seems to play a role in 5-HT-induced antinociception in the facilitated state. |
| Key Words:
antinociception; formalin test; 5-hydroxytryptamine and its receptors; rat; spinal cord |
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