tokens: PC12 sells ( RIKEN Cell Bank , Tsukuba , Japan ) were cultured at 37 degrees C , 5 % CO2 with Dulbecco ' s modified Eagle ' s medium ( DMEM ) supplemented with 5 % heat - inactivated fetal bovine serum ( FBS ) , 10 % heat - inactivated horse serum , and 1 % penicillin .