[Bored chemist]

This has been a silly question  for about 500 years

There's no silly questions, only silly answers...

By the way, 500 years ago we didn't even knew what was a excitotoxin.

I'm guessing it's very hard for you to learn something new, mr chemist.
 

OK
I have learned that you don't understand toxicity.
Here's some comparative tox data for MSG and salt from wiki
"The median lethal dose (LD50) is between 15 and 18 g/kg body weight in rats and mice, respectively, five times greater than the LD50 of salt (3 g/kg in rats)."

Now, as you you have pointed out ( but misunderstood), once the MSG is in the body the amalgamate an d sodium ions separate.
The same is true with salt, it forms hydrated sodium and chloride ions.

Now if we look at those figures, we can see that the lethal dose of salt contains 3/58 i.e about 0.05 moles of sodium ions and the MSG contains about  15/196 i.e.e about 0.075 moles
Since there's more sodium in the MSG than in the salt (at the lethal dose of each) , it can't be the sodium that's causing the toxicity.
So, the toxicity  of the two compounds must be caused by the anions- glutamate or chloride.
And it is clear that glutamate is rather less toxic (in this assay) than chloride.
Something that's less toxic than the commonest anion in the body really isn't very toxic.

[Sharon allen]

monosodium glutamate(msg) is a glutamate amino acid, it is naturally present in some foods.

[alancalverd]

The odd thing about this thread is the absence of any mention of Kwok syndrome. This generally manifests as paresthesia of the upper arms and torso within about 20 minutes of ingesting a substantial bolus of MSG, though various other symptoms including headache are common. It is transient and quickly relieved by drinking copious amounts of water.

There was quite a lot of excitement about it in the late 60s and early 70s and I recall a spectacular outbreak in a London Chinese restaurant one evening where the "special" was soyed pig's tripe: my girlfriend and I suffered partial paralysis within a few seconds of each other, then noticed a "buzz"  throughout the room as others succumbed. Fortunately the waiters were aware of the problem  and rushed about with jugs of water, and order was restored within 5 minutes. Delicious, but best avoided - I've not seen it on a menu since.