Glutamate

Glutamate is an amino acid that acts as a neurotransmitter. Glutamate sends chemical messages in the brain by "exciting" neurons that are sensitive to it. Although it plays a vital role in learning, memory, and brain development, too much glutamate can be toxic. When a person experiences a head injury or stroke, glutamate floods the injured area and kills the neurons by overexciting them, causing brain damage.