The hypothalamus of the brain uses glutamate as a neurotransmitter -it has many
receptors for glutamate. The hypothalamus is not protected from MSG by the blood
brain barrier, since it must monitor levels of substances in the blood, and react
accordingly.
Scientists often joke that the hypothalamus is
responsible for the 4 f's: feeding, fighting, fleeing, and mating.
So it is the part of the brain responsible for the "Fight or Flight" reflex.
The main purpose for food scientists using it in their products is to
stimulate your hunger. Unfortunately, the hypothalamus also regulates
panic and rage as well as directing the entire endocrine system by directing
the pituitary or "master gland".
More info on the hypothalamus, and rage:
http://www.accd.edu/pac/science/hopper/Biol2401/Unit5/NSNotes2.htm
http://www.cnl.salk.edu/~fellous/pubs/emo.pdf
Based on the fact that MSG has been proven to overstimulate cells in the hypothalamus
until they actually died, and that the hypothalamus regulates rage and fear as well as
hunger and body temperature, it might be in our best interest to look more closely at what
violent teenagers have been eating these days.