<Tr> <Th> KEGG </Th> <Td> <Ul> <Li> C00025 </Li> </Ul> </Td> </Tr> <Ul> <Li> C00025 </Li> </Ul> <P> In neuroscience, glutamate refers to the anion of glutamic acid in its role as a neurotransmitter: a chemical that nerve cells use to send signals to other cells . It is by a wide margin the most abundant neurotransmitter in the vertebrate nervous system . It is used by every major excitatory function in the vertebrate brain, accounting in total for well over 90% of the synaptic connections in the human brain . It also serves as the primary neurotransmitter for some localized brain regions, such as cerebellum granule cells . </P> <P> Biochemical receptors for glutamate fall into three major classes, known as AMPA receptors, NMDA receptors, and metabotropic glutamate receptors . A fourth class, known as kainate receptors, are similar in many respects to AMPA receptors, but much less abundant . Many synapses use multiple types of glutamate receptors . AMPA receptors are ionotropic receptors specialized for fast excitation: in many synapses they produce excitatory electrical responses in their targets a fraction of a millisecond after being stimulated . NMDA receptors are also ionotropic, but they differ from AMPA receptors in being permeable, when activated, to calcium . Their properties make them particularly important for learning and memory . Metabotropic receptors act through second messenger systems to create slow, sustained effects on their targets . </P>

What part of the brain does glutamate affect