The NMDA Receptor 1 (GluN1) protein is an essential subunit of NMDA receptors, which are ligand-gated ion channels that play crucial roles in excitatory neurotransmission, synaptic plasticity, learning, and memory in the central nervous system. GluN1 is required for the formation and function of all NMDA receptor complexes, as it binds glycine or D-serine and provides structural support for the receptor. This subunit is widely expressed in neurons and undergoes alternative splicing to produce multiple isoforms, each with distinct functional and pharmacological properties. For example, the presence of exon 5 in GluN1 reduces agonist potency and accelerates receptor deactivation. Additionally, GluN1's intracellular carboxyl-terminal domain interacts with various proteins involved in receptor trafficking and anchoring at synapses. Abnormal activity of GluN1-containing receptors has been implicated in several neurological and psychiatric disorders, making it a target for therapeutic interventions.