Ham-milton said:
Some of that doesn't make any sense, dude. How many people have taken GABA daily for months without any problems?
And we all know that GABA *doesn't* cross the bbb, but you say that it will in your summary.
And you're failing to account for the fact that many of these biosyntheses are rate-limited- as in, you can take all the precursors you want and you won't increase the concentration of the end product beyond a certain, fairly low point.
And do you actually have any refs for your claims that GABA or levoglutamate decrease serotonin and dopamine levels? That just sounds like total bullshit knowing how many people are taking these things for long periods of time, at sometimes large doses without ever incurring any side effects.
Ok... So according to my professor, GABA is a neutral amino acid and therefore uses the neutral amino acid protein transport system.... So therefore it does cross the blood brain barrier. But after going back to sources, it seems as since GABA is a small neutral amino acid it doesn't have as high of an affinity for the transport protein, so it doesn't transport as much. Furthermore, GABA has no action outside the brain. Therefore, if it doesn't cross the blood brain barrier, why are you taking it? To waste money? 8)
For my sources see:
Pardridge, William M. Regulation of Amino Acid Availability to the Brain. Found in Neutrition and the Brain, Vol. 1 edited by R.J. Wurtman and J.J Wurtman. Raven Press, NY, 1977.
Therefore, since you are increasing the amount of GABA, you are increasing the amount crossing the BBB, even if if it isn't to exorbitant amounts.
Also, Serotonin is directly related to the amount of tryptophan in the brain.
See:
Schaechter, J, et al. Tryptophan Availability Modulates Serotonin Release from Rat Hypothalamic Slices. J. Neurochemistry, 1989.
http://www.blackwell-synergy.com/doi/abs/10.1111/j.1471-4159.1989.tb09263.x
Dopamine isn't as related to the concentration of tyrosine, as dopamine is synthesized more redily when the dopageneric neurons are firing. However, the concentrations of tyrosine are still important.
Ackworth, Ian N. Tyrosine: Effects on Catecholamine Release
However, the reduction in serotonin can be accounted for by eating carbs, which can cause an increase in transmission of tryptophan across the BBB. This is because carbs cause an insulin spike which causes the other neutral amino acids to be removed from the blood, while tryptophan is large and non polar and stays bound to the albumin in blood. This increases its relative concentration and facilitates crossing of the blood brain barrier.
Wurtman, R. J. Effects of normal meals rich in carbohydrates or proteins on plasma tryptophan and tyrosine ratios.
http://www.ajcn.org/cgi/content/abstract/77/1/128
Fernstrom, John D. Brain Serotonin Content: Increase Following Ingestion of Carbohydrate Diet. Science, New Series, Volume 174, Dec. 3 1971.
http://www.sciencemag.org/cgi/content/abstract/174/4013/1023
Furthermore, there is no one who will tell me that threonine is not a larger neutral amino acid and will compete with these other amino acids.
On another note: GABA is made from Glutamate. Glutamate is found in surplus in the brain, so therefore it is definitely not the limiting reagant in the transformation. However, vitamin B6, or Pyridoxal P is the limiting reagant in the decarboxylation reaction. Therefore, I would say don't waste your money on GABA, "which doesn't cross the blood brain barrier," and just use vitamin B.
Ham-milton: I would like some sources telling me that GABA doesn't cross the BBB (as my sources seem to say they do, just with a bit less affinity). And I would also like sources about the rate limiting syntheses of these neurotransmitters, as my sources seem to say the opposite. (except in GABA, and glu...)
