Micro-iontophoretic nicotine application. (A) Cultured mouse hippocampal neurons transduced with AAV_iNicSnFR3b_ER. A nicotine-containing micro-iontophoretic pipette was positioned <10 µm above the cell in ROI 1. A 10-nA outward current pulse (32-s duration) was delivered. Most cells in the area showed fluorescence increases. (B) Fluorescence traces recorded simultaneously for cells at three distances from the pipette.