BINDING CHARACTERISTICS OF A POTENT AMPA RECEPTOR ANTAGONIST [H-3]RO-48-8587 IN RAT-BRAIN

A new AMPA receptor antagonist, Ro 48-8587, was characterized pharmaco logically in vitro. It is highly potent and selective for AMPA recepto rs as shown by its effects on [H-3]AMPA, [H-3] kainate, and [H-3] MK-8 01 binding to rat brain membranes and on AMPA- or NMDA-induced depolar ization in rat cortical wedges. [3H]Ro 48-8587 bound with a high affin ity (K-D = 3 nM) to a single population of binding sites with a B-max of 1 pmol/mg of protein in rat whole brain membranes. [3H]Ro 48-8587 b inding to rat whole brain membranes was inhibited by several compounds with the following rank order of potency: Ro 48-8587 > 6-nitro-7-sulp hamoylbenzo [f] quinoxaline-2,3-dione (NBQX) > YM 90K > 6-cyano-7-nitr oquinoxaline-2,3-dione (CNQX) > quisqualate >AMPA > glutamate > kainat e > NMDA. The distribution and abundance of specific binding sites (si milar to 95% of total) in sections of rat CNS, revealed by quantitativ e receptor radioautography and image analysis, indicated a very discre te localization. Highest binding values were observed in cortical laye rs (binding in layers 1 and 2 > binding in layers 3-6), hippocampal fo rmation, striatum, dorsal septum, reticular thalamic nucleus, cerebell ar molecular layer, and spinal cord dorsal horn. Al f nM, the values f or specific binding were highest in the cortical layers 1 and 2 and lo west in the brainstem (similar to 2,6 and 0.4 pmol/mg of protein, resp ectively). Ro 48-8587 is a potent and selective AMPA receptor antagoni st with improved binding characteristics (higher affinity, selectivity , and specific binding) compared with those previously reported.