Fig. 4. (  A ) Direct activation of  N -methyl-d-aspartate receptors by Ultiva®. Representative trace of  N -methyl-d-aspartate current induced by application of Ultiva® containing 50 μm remifentanil hydrochloride and 3 mm glycine. Whole cell current is first recorded in control conditions (Ctrl). Ultiva® added to the perfusing bath induces an inward current. When this current remains stable, 50 μm d-2-amino-5-phosphonovalerate (D-AP5) is added to the perfusing bath. Ultiva®-induced current is abolished by application of 50 μm D-AP5. (  B ) There is a significant difference between the current recorded during control conditions and the one recorded during application of Ultiva® containing 50 μm remifentanil hydrochloride and 3 mm glycine (n = 5, *  P < 0.05). There is no significant difference between the current recorded during application of D-AP5 and the one recorded during control conditions (n = 5,  P > 0.05).