ADCYAP1R1 and neuroblastoma: The positive correlation of the PAC1 expression level with its basal activity was further determined using a Tet (tetracycline)-on inducible PAC1 expression system with the controlled expression of PAC1 by doxycycline (Dox) and using the down-regulation of PAC1 with shRNA in neuro2a neuroblastoma cells with a naturally high expression of PAC1.