Fig. 5

Chemogenetic manipulation of RVM 5-HT neurons regulated the hyperalgesia after delayed REOI and PEOI-induced hyperalgesia. A Schematic diagram of the experimental time course of HWT measurements (n = 6–8 in each group). B Injection of viruses into the RVM region. C Changes in HWTs in REOI rats expressing hM4Di, hM3Dq, or mCherry respectively. Results represent mean ± SD; two-way repeated measures ANOVA, followed by Tukey’s multiple-comparison test. P = 0.0013, 0.0057, and 0.0001 for the mCherry-expressing, hM4Di-expressing, or hM3Dq-expressing REOI groups, respectively, before CNO injection on day 14 vs. baseline. ** P < 0.01, *** P < 0.001, the hM4Di-expressing REOI group vs. the mCherry-expressing REOI group. &&& P < 0.001, the hM3Dq-expressing REOI group vs. the mCherry-expressing REOI group. (D) Changes in HWTs in PEOI rats expressing hM4Di, hM3Dq, or mCherry respectively. Results represent mean ± SD; two-way repeated measures ANOVA, followed by Tukey’s multiple-comparison test. P = 0.0055, 0.0122, and 0.0339 for the mCherry-expressing, hM4Di-expressing, or hM3Dq-expressing PEOI groups, respectively, before CNO injection on day 14 vs. baseline. && P < 0.01, &&& P < 0.001, the hM3Dq-expressing PEOI group vs. the mCherry-expressing PEOI group. E ΔHWT in REOI or PEOI rats expressing hM4Di, hM3Dq or mCherry respectively. Results represent mean ± SD; two-way ANOVA, followed by Tukey’s multiple-comparison test. F Representative images of mCherry expression in the RVM and the histological verification of the injection site. Scale bar, 500 μm. GiA, nucleus gigantocellularis pars α; NRM, nucleus raphe magnus; ml, medial lemniscus; Py, pyramidal tract. G High magnification photographs of the area encircled in red or blue rectangle respectively in F show the co-expression of Tph2 with mCherry in the RVM (the white arrows). Scale bar, 50 μm. H The infection rate and specificity of the viruses in the RVM were examined by histological verification. CNO, clozapine. Tph2, tryptophan hydroxylase 2