I'm still not sure what to think about manganese deficiency since I get plenty from my diet, but I did find this conversation about manganese and excitotoxicity between Rich and Asklipia interesting.
I have wondered about manganese supplementation for myself. Supposedly the oral bioavailability in many foods is not very high. So hard to judge if I get enough or not. The hair analysis I did showed it was low but that may mean it is sitting in biounavailable forms in the interstitial spaces.
However, I am not sure I buy into a strict anti-glutamate food warning at least for people with normal blood brain barrier integrity. (Yes I know many people are getting sick of me bringing up the blood brain barrier and the assumption of normal is probably ill advised at best for those of us on these forums).
Rich and I had a private discussion on this and never really agreed I suppose, but at least he tended to not favor the low protein restricted diets for CFS patients.
The reason is that while glutamate is excitatory it cannot cross the blood brain barrier under regular conditions. The tight regulation of glutamate and GABA in the CNS vs the periphery is very important to the body and CNS. The only way to cross the blood brain barrier is by conversion back to glutamine and the glutamine shuttle between the brain and body is an exquisite piece of engineering when working right.
Things like MSG are different. MSG is a CNS absorbable form of glutamate. Just like Picalon is a highly CNS absorbable form of GABA (beware tolerance effects though).
That being said ingested glutamate can certainly affect the body especially the GI tract and the ANS at the various peripheral nerve plexuses. The latter of these could maybe a gateway to the brain via direct signaling connection that could overload specific parts of the brain but that is way beyond my knowledge level.
True glutamate excitotoxicity (which many of us have sadly experienced) is usually brought on by dysfunction in the regulation of the glial cells and / or astrocytes involving the production, conversion, or catabolism (don't forget that one) of the "big three" of glutamate, GABA, and glutamine in the actual CNS. Don't let anyone kid you while dopamine, serotonin, NE and acetylcholine are all important in the CNS, something like 60-70% of your glial cells in your brain are devoted to one of those "big three".
The exception for the absorption argument is again people with BBB integrity issues but even then it is not clear how likely ingestion effects would be the primary cause of excitotoxicity unless large amounts were taken. And before people jump in with the sensitivity argument, ask yourself what is the mechanism why that person is sensitive to say ingested glutamate? E.g. how does it cause a CNS excitotoxic problem if they eat a bunch of soy? For some of us on these forums it probably would, but again how does it happen? Don't just bail things out by only calling it "sensitivity". That mantra usually gives no insight.
On the other hand a problem with glutamine synthetase activity in the CNS can be a REAL problem. Remember that glutamine synthetase is also the only real way for the CNS to remove ammonia in any significant amount.
I personally don't agree with the alternative practitioners who have pushed the idea of no glutamate in all protein rich foods. Studies have shown the glutamate in things like meat and milk do not demonstrably raise serum glutamate levels in the periphery as they are efficiently converted to glutamine in the gut (unless the person has suffered GI damage due to Celiac's or related conditions). The glutamate in grains, soy, etc. are a different story and can flood the periphery but the BBB is supposed to be the guard / watchdog for the CNS. All of this is probably out the window when dealing with autistic children as someone like Dr Yasko and others since there a lot of things have to be based purely on clinical observations of sensitivities.
Personally I think the over-production of ammonia can be a big excitotoxic trigger in the CNS that can really imbalance the neurotransmitters and essentially shift body chemistry. I experienced this first hand last week when left to my own devices I ate a 1.5 lbs of hamburger meat and 4 chicken legs at one sitting ... not fun ... all I can say is I am thankful for Yucca for such emergencies.
Now I am saying all of this one caveat. Due to my autoimmune disease (SPS), glutamate in the CNS can be a real problem for me. My blood brain barrier is a pretty leaky wall (though it has improved some over time). And I have Celiac's. Even then glutamate in nuts and meat don't seem to affect me (unless I go berserk in the aforementioned episode, and even then I had mostly problems with muscle pain not CNS problems, i.e. I slept fine and had no insomnia, just cramped everywhere in my skeletal muscles). So take what I say with a grain of salt.
