Optical stimulation increases c-fos expression in RVM 5-HT neurons. (A) Representative images showing anti-c-fos, anti-GFP and merged staining in the RVM of TPH2-ChR2 mice without (top row) and after single light stimulation (bottom row). Scale bars =100 μM. (B) Images in groups similar to those in (A) but in higher magnification (Scale bars =50 μM). (C and D) Summarized data of intensity of c-fos staining (C) and percentage of c-fos-positive cells vs. DAPI-positive cells (D) in the RVM of TPH2-ChR2 mice (9 slices from 3 different mice for each group). *** p <0.001 (unpaired t test).