
In order to excitotoxin effects of MSG, MSG that in blood must go through 
blood-brain barrier that I am not sure MSG can go through or not. In normal condition, the concentration of glutamate in the cerebrospinal fluid is about 
2 uM that is high enough to activate one type of glutamate receptor-the NMDA
receptor. But the question is Neuron and glial cell in the brain have a lots of transport to get glutamate into Neuron or glial. So no one know exact concentration of glutamate is around neurons. 