Wikipedia
Anion of glutamic acid in its role as a neurotransmitter
Summary
Glutamate is an amino acid, and a neurotransmitter. It is by a wide margin the most abundant excitatory neurotransmitter in the vertebrate nervous system. It is used by every major excitatory function in the vertebrate brain, estimated to account for 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.