SIM-A9 cells (P8) were cultured for 48 h and incubated with 50 μM ATP for 2 h. Control, untreated cells, and treated cells were fixed with 4% PFA, blocked to prevent non-specific antibody binding, and immunostained with mouse-P2X4R (1:250), rabbit-Iba1 (1:500), and BDNF (1:500) primary antibodies, respectively. P2X4R was counterstained with anti-mouse AF555 (green), Iba1 and BDNF with anti-rabbit AF488 (red), and the nucleus was stained with Hoechst 33342 dye (blue). Images were captured under the phase-contrast setting (Transmitted), DAPI (blue), green or red channels, and merged in the overlay image. Triplicate samples were analyzed in two independent experiments. Scale bar = 100 μm. All images were cropped at the same scale using Adobe Photoshop CC 19.1.9 for clarity and conciseness of the presentation. The full length of a representative phase-contrast image for P2X4R is presented in S1 Fig.