Food Components to Enhance Performance An Evaluation of Potential Performance-Enhancing Food Components for Operational Rations (1994) / Chapter Skim
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16. Tyrosine and Glucose Modulation of Cognitive Deficits Resulting from Cold Stress
16. Tyrosine and Glucose Modulation of Cognitive Deficits Resulting from Cold Stress
Pages 301-320
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Thomas, John Schrot, and David Shorties INTRODUCTION COLD STRESS AND WORKING MEMORY Research at the Naval Medical Research Institute on the effects of nutritional components on performance has centered primarily on alleviation of cold-induced impairment of short-term or working memory by the catecholamine precursor tyrosine and the simple sugar glucose. Efforts have focused on measures of working memory specifically, since research has shown that working memory is uniquely susceptible to disruption by cold stress.
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Rather, research at the Naval Medical Research Institute has focused on the effects of exposure to cold air stress that does not result in an obvious drop in core temperature, as determined by standard thennometry methods. Under these conditions, exposure to cold ambient air (2-5 °C)
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2 8 ] 6 DELAY FIGURE 16-2 Matching accuracy of human subjects performing the delayed matching-tosample task during exposure to ambient temperatures of 23° and 4°C.
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may reflect distinct neurobiological processes which, as described below, appear to influence the conditions in which nutritional factors ameliorate cold-induced memory decrements. To elucidate the basic mechanisms that underlie the cold-induced memory deficit and to test prospective agents that could alleviate these effects, an animal model was developed in which rats performed a DMTS task.
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They found that during exposure to cold air, the temperature in the hippocampus, a key brain structure involved in the modulation of working memory, was decreased by 1°C compared with the temperature when the DMTS task was performed during normothermic conditions. This finding added some weight to the suggestion that subtle temperature gradients in the brain may underlie many cold-induced deficits in cognition (Pozos, 1986~.
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indicated that tyrosine partially alleviated the deficit in matching accuracy. Given the success in reducing the cold-induced memory impairment in rats, the emphasis was shifted to examine the effects of tyrosine in human subjects exposed to cold stress in the environmental chamber at the Naval Medical Research Institute, Bethesda, Maryland (Shurtleff, et al., 1994~.
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Tyrosine Studies During Field Operations in the Cold Once the tyrosine-induced alleviation of a cold-induced impairment of working memory in the laboratory chamber with humans was demonstrated, the next logical step was to determine whether tyrosine pretreatment would be beneficial in field situations with military personnel operating in a cold environment. Figure 16-5 shows the effects of tyrosine pretreatment on military personnel under field conditions.
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When taken together with previous research demonstrating tyrosine's beneficial effects in military personnel under a variety of stressful conditions with several different test parameters (Banderet and Lieberman, 1989) , it is clear that tyrosine administration is capable of improving cognitive performance in military personnel exposed to cold stress.
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Conclusions and Recommendations Regarding the Use of Tyrosine The observation that tyrosine alleviates cold-induced impairment of working memory and timing behavior is consistent with the demonstrated efficacy of tyrosine in a variety of test situations with both human and animal subjects. Of particular relevance to the recommendation that tyrosine might be given to deployed military personnel are the findings of Banderet and Lieberman (1989)
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Tyrosine has been found to block effectively the cold-induced deficits in working memory observed in humans both in the laboratory and in military field operations in cold weather. Taken together, these studies indicate that tyrosine certainly has potential as a nutritional component for improving the compromised performance of military personnel operating under stressful conditions (Owasoyo et al.,1992; Salter, 1989)
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demonstrated that chronic administration of CRF produces a dramatic increase in TH in the locus ceruleus. These studies indicate that chronic stress produces enduring alterations in the noradrenergic and CRF stress response systems.
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In that study, the exposure to the cold air stress produced an impairment of matching accuracy at all of the delays (Figure 16-7~. Recall from the previous discussion that when cold induces a decrease in matching accuracy at the short delays, the effect of cold on working memory .
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The data showing the effects of a 50-mg/kg dose of glucose on the number of errors within a test session as a function of cold stress are depicted in Figure 16-8. In a procedure in which the acquisition of the response sequence is protracted over multiple trials, glucose not only decreased the number of errors across the session during cold stress, but it also produced fewer errors during exposure to 23°C.
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Sal= saline; Glu= glucose. Mechanisms of Action of Glucose on Working Memory The cold-induced encoding observed when rats perform the DMTS task is similar to the effects of scopolamine, an acetylcholine (ACh)
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In addition, there has been recent speculation, supported by experimental data, that many of the putative cognition enhancers, i.e., nootropic drugs, which might be recommended for use in improving cognitive performance in military personnel, produce their beneficial effects by increasing the availability and uptake of glucose in the CNS (Week, 1989~. Conclusions and Recommendations Regarding Glucose as a Cognition Enhancer The results of studies with glucose indicate that, as a nutritional component, it has the potential to enhance the performance of military personnel in operational environments.
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· Progress with glucose as a perfonnar~ce enhancer during cold-induced stress is not as advanced as progress with tyrosine. The logical next step for glucose is to examine its effects in military personnel in studies in controlled environmental chambers and in field exercises and to consider its effects under acute and chronic stress conditions as well.
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VanSomeren, and A.H. Wolff 1983a Memory registration at mildly depressed deep body temperatures.
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Ragozzino, M.E., and P.E. Gold 1991 Glucose effects on mecamylamine-induced memory deficits and decreases in locomotor activity in mice.
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Actually, your point had to do more with chronic stress than with chronic administration. STEPHEN AHLERS: Exactly.
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STEPHEN AHLERS: That is one of our next experiments. That is actually the reason we used CRF to induce the stress response, to get around the potentially confounding differences involved with the administration of physical stressors.
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