Development of GluN2A NMDA receptor positive allosteric modulators: Recent advances and perspectives

N-methyl-d-aspartate (NMDA) receptors, functioning as glutamate-gated ion channels, mediate the permeation of Ca²⁺ and are essential for excitatory synaptic transmission and synaptic plasticity within the central nervous system (CNS). During brain development, there is a switch from an early dominance of GluN2B subunit expression to the incorporation of GluN2A subunits at mature synapses. NMDARs hypofunction is implicated in various psychiatric disorders, and activation of NMDARs containing GluN2A has recently attracted attention as a promising therapeutic approach for treating these diseases. This review focuses on the selective positive allosteric modulators (PAMs) that specifically target the ligand-binding domain (LBD) and N-terminal domain (NTD) regions of GluN2A subtype, as well as non-subunit selective PAMs, and discusses their implications in neuropsychiatric diseases such as stroke, depression, Alzheimer's disease, and Huntington's disease.