[3H](+)MK801 radioligand binding assay at the N-methyl-D-aspartate receptor.

The N-methyl-D-aspartate subtype of glutamate receptor is unusual in that it requires two endogenous agonists for activation. Thus, in addition to glutamate, the amino acid glycine (or possibly D-serine) is an essential co-agonist. This unit presents a radioligand binding protocol that detects ligand activity at the NMDA receptor-associated glycine site. This is a convenient approach that exploits the ability of NMDA receptor modulators to alter the kinetics of ligands that bind to the channel-blocking site of the NMDA receptor. This protocol takes advantage of one of the most potent and specific ligands that bind to this receptor, in this case [(3)H](+)MK801. Importantly, this assay can detect and differentiate agonists and antagonists that bind to the glycine site. A protocol for the measurement of glycine site activity with [(3)H](+)MK801 binding is provided, along with support protocols that provide information to aid in the design of assays of agonists and antagonists of the glycine site, and data analysis.