Fig. 5. (A ) The competitive glutamate binding site antagonist D-AP5 (1 mm; white bars ) inhibits glutamate/glycine-induced currents (EC50) (*P < 0.05) but does not affect Ultiva®-induced (remifentanil 0.1 mm plus glycine 3.1 mm) responses (n > 10; vertical bars ± SEMs). (B ) The noncompetitive N -methyl-d-aspartate receptor channel pore blocker MK-801 inhibits N -methyl-d-aspartate receptor responses (NR1A/2A) to Ultiva®(remifentanil 0.1 mm plus glycine 3.1 mm) and glutamate/glycine (EC50) in a concentration-dependent manner (*P < 0.05; n = 10; vertical bars ± SEMs).