NMDA receptor antagonists, particularly these targeting the GluN2B subunit are of therapeutic interest for the treatment of severe mood disorders. The receptor occupancy profiles of several NMDA receptor antagonists (30mg/kg, s.c.) were compared in mouse hippocampus by ex vivo autoradiography using [3H]MK-801, a non-selective NMDA channel blocker, and [3H]ifenprodil a selective GluN2B antagonist. Subcutaneous administration of ketamine ((RS)-2-(2-Chlorophenyl)-2-(methylamino)cyclohexanone) and memantine (3,5-dimethyladamantan-1-amine) inhibited [3H]MK-801 but not [3H]ifenprodil binding in mouse hippocampus. Ketamine reached maximal occupancy of [3H]MK-801 binding sites after 15min and rapidly cleared from the brain with no significant level of occupancy measured at the 1h time point. Memantine significantly occupied [3H]MK-801 binding sites throughout the 6h time course. The selective GluN2B antagonist CP101,606 ((1S,2S)-1-(4-hydroxyphenyl)-2-(4-hydroxy-4-phenylpiperidino)-1-propanol) and Ro 25-6981 ((αR,βS)-α-(4-Hydroxyphenyl)-β-methyl-4-(phenylmethyl)-1-piperidinepropanol maleate) inhibited [3H]ifenprodil but not [3H]MK-801 binding and significant levels of occupancy (above 50%) were measured throughout the 6h time course. These data highlight the unique quick pulse target engagement profile of ketamine compared to other NMDA receptor antagonists.