Expression of 5-HT(2A) receptor mRNA in some nuclei of brain stem enhanced in monoarthritic rats.

The present study was designed to investigate the expression of 5-hydroxytryptamine (5-HT) (2A) receptor mRNA in the nucleus of raphe magnus (NRM), ventrolateral periaqueductal gray (vlPAG) and dorsal raphe nucleus (DRN) in a monoarthritic rat model using an in situ hybridization technique. 5-HT(2A) receptor mRNA was expressed with low to moderate levels in NRM, vlPAG and DRN. After complete Freund's adjuvant (CFA)-induced monoarthritis, a significant increase in 5-HT(2A) receptor mRNA expression was observed in bilateral NRM, vlPAG and DRN, and the change lasted, at least, for 2 weeks. This result indicates that the synthesis of 5-HT(2A) receptor is enhanced in bilateral NRM, vlPAG and DRN of monoarthritic rats, suggesting that 5-HT(2A) receptor is involved in the central regulation of pain transmission following CFA-induced chronic inflammation.