Monosodium glutamate (MSG is the sodium salt of the amino acid glutamate). Glutamate, in addition to serving as one of the amino acids found in proteins, is also an excitatory amino acid and activates other neurons in the brain by binding to a specific type of glutamate receptors. This process activates calcium release, which in turn affects the intra-cranial blood vessel tone. This is one of the crucial steps in the process of migraine generation.