Excitotoxicity due to glutamate occurs as part of the ischemic cascade and is associated with stroke and diseases like amyotrophic lateral sclerosis, lathyrism, autism, some forms of mental retardation and Alzheimer's disease.
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Glutamic acid is often used as a food additive and flavour enhancer in the form of its sodium salt, monosodium glutamate (MSG).

All meats, poultry, fish, eggs, dairy products, as well as kombu are excellent sources of glutamic acid. Some protein-rich plant foods also serve as sources. Ninety-five percent of the dietary glutamate is metabolized by intestinal cells in a first pass.

http://en.wikipedia.org/wiki/Glutamate