Glutamate receptors mediate most excitatory neurotransmission in the brain and play an important role in neural plasticity, neural development and neurodegeneration. Ionotropic glutamate receptors are categorized into NMDA receptors and kainate/AMPA receptors, both of which contain glutamate-gated, cation-specific ion channels. Synaptic and extrasynaptic NMDA receptors have been shown to have opposite effects on neuronal survival, CREB function and gene regulation. Gcom1 (GRINL1A complex locus protein 1), also known as GUP (GRINL1A upstream protein) and Gcom (GRINL1A combined protein), is a 466 amino acid protein that is a component of the GRINL1A complex transcription unit, which is thought to be involved in the modulation of glutamatergic neurotransmission through interaction with the NR1 subunit of the NMDA receptor. Gcom1 is expressed in small intestine, lung, liver, heart, skeletal muscle, testis and prostate and also colocalizes with NR1 in cortical and hippocampal neurons. There are eleven isoforms of Gcom1 that are produced as a result of alternative splicing events.