Expression of 5-HT1A receptor mRNA in rat dorsal raphe nucleus and ventrolateral periaqueductal gray neurons after peripheral inflammation

In the present study we observed the expression of 5-hydroxytryptamine (5-HT)(IA) receptor mRNA in the dorsal raphe nucleus (DRN) and ventrolateral periaqueductal gray (vlPAG) neurons, especially in 5-HT immunoreactive neurons (5-HT-IR), using in situ hybridization (ISH) and double staining with fluorescent ISH (FISH) and immunohistochemical (FIH) techniques. The findings of this study demonstrated that 5HT(IA) receptor mRNA was expressed with moderate to high level in the DRN and vlPAG neurons. Following carrageenan inflammation, the expression of 5-HTIA receptor mRNA in the DRN and bilateral vlPAG neurons was significantly increased. The peak occurred at 3-8 h followed by a clear decrease at 24 h, which basically corresponded to the time-course of behavioral hyperalgesia. Moderate 5-HTIA receptor mRNA and 5-HT immunoreactive (5-HT-IR) double-labeled cells were observed in the DRN and vlPAG, suggesting that some of 5-HTIA receptors in the DRN and vlPAG may be autoreceptors. Eight hours after carrageenan injection, the number of the double labeled cells was significantly increased. These results suggest that the synthesis of 5-HTIA receptors, including autoreceptors, is increased in the DRN and vlPAG during peripheral inflammation. NeuroReport 11:3361-3365 (C) 2000 Lippincott Williams & Wilkins.