I do whole cell voltage clamp recordings from dentate gyrus granule cells from different age groups (p9 to adults). I am trying to block NR2B subunits of NMDA receptors sing ifenprodil. I add NBQX (10 micromolar), bicuculline (10 micromolar) and then ifenprodil (3 micromolar). Whenever I added ifenprodil (dissolved in water), I see a huge potentiation of NMDA currents (upto 100 pA increase). Could anyone has any idea what is going on?