Food Components to Enhance Performance An Evaluation of Potential Performance-Enhancing Food Components for Operational Rations (1994) / Chapter Skim
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13. Effects of Nutrients on Neurotransmitter Release
13. Effects of Nutrients on Neurotransmitter Release
Pages 239-262
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From page 239... ...
Another type of process that particularly affects the release of amine neurotransmitters depends on changes in the composition of the blood plasma induced by eating or by prolonged physical activity. Changes in plasma levels of choline or of certain amino acids lead to changes in brain levels of the 02139 ~ Portions of this manuscript have been adapted from Wurtman (1988)
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From page 240... ...
amino acid tryptophan were found to have risen, thus increasing the substrate saturation of the enzyme that controls serotonin synthesis, tryptophan hydroxylase. The resulting increase in brain serotonin levels was associated with an increase in brain levels of serotonin's metabolite, 5-hydroxyindole acetic acid, thus suggesting that serotonin release had also been enhanced.
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From page 241... ...
Insulin causes nonesterified fatty acid molecules to dissociate from albumin and to enter adipocytes. This dissociation increases the protein's capacity to bind circulating tryptophan; hence, whatever reduction insulin causes in free plasma tryptophan levels is compensated for by a rise in the tryptophan bound to albumin, yielding no net change in total plasma tryptophan levels in humans (Madras et al., 1974~.
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From page 242... ...
However, when rats were given small doses of tryptophan that were sufficient to raise brain tryptophan levels but not beyond their normal peaks or when they consumed a carbohydrate-rich meal, which raised brain tryptophan levels physiologically, no decreases in rapine firing occurred. Hence, food-induced changes in serotonin synthesis were found to affect the amounts of serotonin released per firing without slowing the neuron's firing frequencies, thus "allowing" modulation of the net output of information from serotonergic neurons.
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From page 243... ...
Perhaps these neurons participate in a feedback loop through which the composition of breakfast (i.e., its proportions of protein and carbohydrate) can, by increasing or decreasing brain serotonin levels, influence the choice of lunch.
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From page 244... ...
(The carbohydrates, by increasing intrasynaptic serotonin, would mimic the neurochemical actions of bona fide antidepressant drugs, such as the MAO inhibitors and tricyclic compounds tWu~l~an, 19831.) Other patients might complain of depression, and their carbohydrate craving and weight gain would be perceived as secondary problems.
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From page 245... ...
Pharmacological doses of the amino acid histidine do elevate histamine levels within nerve terminals, and the administration of threonine, a substrate for the enzyme that normally forms glycine from serine, can elevate glycine levels within spinal cord neurons (and, probably, thereby ameliorate some of the clinical manifestations of spasticity [Growdon et al., 19911~. One large family of neurotransmitters, the peptides, is almost certainly not subject to precursor control.
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From page 246... ...
, even though these are probably the most abundant neurotransmitters in the brain. It is difficult to do experiments on these relationships; the precise biochemical pathways that synthesize glutamate and aspartate within nerve terminals are not well established, and for GABA, although it is well established that its precursor is glutamate, brain levels of that amino acid cannot be raised experimentally without sorely disrupting normal brain functions.
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From page 247... ...
, the supplemental tyrosine caused a marked augmentation of catecholamine release (Wurtman, 1988;Wurtman etal., 1980~.These initial observations formed the basis for the hypothesis that catecholaminergic neurons become tyrosine sensitive when they are physiologically active and lose this capacity when they are quiescent. The biochemical mechanism that couples a neuron's firing frequency to its ability to respond to supplemental tyrosine involves phosphorylation of the tyrosine hydroxylase enzyme protein, a process that occurs when the neurons fire.
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From page 248... ...
, and this phospholipid serves as a reservoir of free choline, much as bone and albumin serve as reservoirs for calcium and essential amino acids. It has been suggested that a prolonged imbalance between the amounts of free choline available to a cholinergic neuron and the amounts needed for acetylcholine synthesis might alter the dynamics of membrane phospholipids to the point of interfering with normal neuronal functioning ("autocannibalism")
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From page 249... ...
, the incorporation of preexisting free choline via the CDP-choline cycle, or the incorporation of free choline via the base exchange pathway (in which a choline molecule substitutes for the ethanolamine in PE or the serine in phosphatidylserine EPSON. Quite possibly, the different varieties of PC may subserve distinct functions; for example, one type of PC, distinguished by its fatty acid composition or its mode of synthesis, could be preferentially utilized to provide a choline source for acetylcholine synthesis or could be formed preferentially during the processes of cell division or synaptic remodeling.
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From page 250... ...
Since low brain choline levels both impair acetylcholine synthesis and accelerate the breakdown of membrane PC and since adequate acetylcholine may be needed to prevent the formation of the amyloid protein of Alzheimer's disease (Nitsch et al., 1992b) , supplemental choline and ethanolamine could have a role in the prevention of this disease.
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From page 251... ...
, then perhaps they Carl be designated as foods. · Considerable additional research should be done to identify special populations with unusual responses to foods or nutrients that affect neurotransmitters (e.g., the carbohydrate cravers who overconsume carbohydrate-rich snacks in order to relieve depressive symptoms)
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From page 252... ...
Wurtman 1971 Brain serotonin content: Physiological dependence on plasma tryptophan levels. Science 173:149-152.
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From page 253... ...
Wurunan 1986 Meal composition and plasma amino acid ratios: Effects of various proteins or carbohydrates, and of various protein concen~ations. Metabolism 35:837-842.
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From page 254... ...
JOHN IVY: Let me back up. I think if you can get the fat in and get it converted out of the free fatty acids or somehow get large amounts of mediumchain triglycerides in, which seems to be difficult—I do not know all the ins
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From page 255... ...
Then you turned right around and said that increasing free fatty acids would also do that. I think that, mechanistically, when one is up, the other is down; so it should not work that way.
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From page 256... ...
EDWARD HORTON: If you have a substantial amount of free fatty acids in the blood, the rate of uptake of muscle free fatty acids is somewhat proportional to the amount available. You increase beta-oxidation.
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From page 257... ...
That certainly has to have an impact on muscle strength and for its immobilization of amino acids for gluconeogenesis, for example. I think there is some real need for studies in that area that look at the effect of the stress hormone response, for example, on gluconeogenesis and glucose output in the liver when you may have a limitation of substrate in the form of amino acid substrates.
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From page 258... ...
ROBERT NESHEIM: Yes, plenty of sleep. MELVIN MATHIAS: John Ivy, you were alluding to this branched-chain amino acid cocktail and exercise enhancement.
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From page 259... ...
Quantitatively, it is just a very small thing. I cannot believe that it has any major effect on exercise performance in the same way that giving a carbohydrate supplement would or from trying to get the body to use more fatty acids and spare carbohydrates.
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From page 260... ...
It does not matter because albumin-bound tryptophan is transported into the brain about 79 percent as effectively as free tryptophan. There is a slight retardation associated with binding of the tryptophan molecule to albumin, but it is so slight that unless you have a mega increase in free fatty acid levels, it is not going to matter or have much of an effect on brain tryptophan levels.
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From page 261... ...
Go back to the classic George Cahill-type studies. They decrease their gluconeogenic amino acids, they slow down hepatic glucose production to about half of normal, and basically reach an adapted state.
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