L-Glutamate is the major excitatory neurotransmitter in the mammalian CNS, acting through both ligand gated ion channels (ionotropic receptors) and G-protein coupled (metabotropic) receptors. As such the glutamate receptors play a vital role in the mediation of excitatory synaptic transmission. The ionotropic glutamate receptors are multimeric assemblies of four or five subunits, and are subdivided into three groups (AMPA, NMDA and Kainate receptors) based on their pharmacology structural similarities Glutamate Receptor 3 is a ionotropic, AMPA-selective, membrane bound protein widely distributed in the CNS. Predominant expression is seen in the neuronal cells of the cerebral cortex, dentate gyrus, and glial cells throughout brain regions. AMPA receptors mediate fast synaptic transmission in the CNS and are composed of subunits GluR1-4, products from separate genes. Glutamate Receptor 3 exists in 2 named isoforms - Flip and Flop, produced by alternative splicing.