Figure 5. Involvement of 5-HT_2A and 5-HT₇ receptors in the potentiating effects of 5-HT.

A, RT-PCR analysis of 5-HT receptor mRNA. Specific mRNA primers for each 5-HT receptor and β-actin were used for RT-PCR analysis of cDNA synthesis from total RNA of neonatal rat DRG. The expected size of mRNA for each subtype was detected by each primer. Size markers (bp) are shown on the left. B, effects of 5-HT_2A and 5-HT₇ agonists on the capsaicin-induced [Ca²⁺]_i increases. DOI (20 μm, n = 20, N = 3), a 5-HT_2A agonist and 8-OH-DPAT (20 μm, n = 52, N = 4), a 5-HT₇ agonist, were used. The panel shows summarized [Ca²⁺]_i increases induced by capsaicin (30 nm) before and during the application of each 5-HT agonist. C, inhibitory effects of 5-HT antagonists on 5-HT-induced potentiation of [Ca²⁺]_i responses to capsaicin. Ketanserin (+ketan, 20 μm, n = 38, N = 4), a 5-HT_2A antagonist, and SB269970 (+SB, 20 μm, n = 46, N = 4), a 5-HT₇ antagonist, were used. 5-HT significantly potentiated the capsaicin-induced [Ca²⁺]_i increases but it was suppressed by the simultaneous application of a 5-HT_2A or 5-HT₇ antagonist. ** P < 0.01; NS, not significant. For the experimental protocol, see Results.