TACR1 and neuroblastoma: To inquire whether TACR1 signaling leads to increased proliferative capacity in neuroblastoma cells, we treated IMR5 cells, which express high levels of TACR1 as well as high levels of p-SRC, with the TACR1 ligand, substance P. Treatment with substance P increased the relative number of viable IMR5 cells over time in 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays (Figure 2A), suggesting that TACR1 activity might be required for IMR5 cell survival.