Ro 25-6981 is a highly potent and selective blocker of N-methyl-D-aspartate receptors containing the NR2B subunit. Ro 25-6981 inhibited 3H-MK-801 binding to rat forebrain membranes in a biphasic manner with IC50 of 0.003 microM and 149 microM for high- (about 60%) and low-affinity sites, respectively. NMDA receptor subtypes expressed in Xenopus oocytes were blocked with IC50 of 0.009 microM and 52 microM for the subunit combinations NR1C & NR2B and NR1C & NR2A, respectively, which indicated a >5000-fold selectivity. References: Szczurowska E, Mares P. Different action of a specific NR2B/NMDA antagonist Ro 25-6981 on cortical evoked potentials and epileptic afterdischarges in immature rats. Brain Res Bull. 2015 Feb;111-8. doi: 10.1016/j.brainresbull.2014.11.001. Epub 2014 Nov 11. PubMed PMID: 25446739.