Glutamate (neurotransmitter)
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 excitatory 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.
Addiction psychology
The neurochemical, glutamate is the most abundant neurochemical in the brain. It is critical in memory consolidation. When an addict discovers an addicting behavior, glutamate plays a role by creating the drug cues. It is the neurochemical in motivation which initiates the drug seeking, thus creating the addiction.