首页
登录
职称英语
It was once believed that the brain was independent of metabolic processes o
It was once believed that the brain was independent of metabolic processes o
游客
2024-01-12
7
管理
问题
It was once believed that the brain was independent of metabolic processes occurring elsewhere in the body. In recent studies, however, we have discov- ered that the production and release in brain neurons of the neurotransmitter serotonin(neurotransmitters are compounds that neurons use to transmit signals to other cells)depend directly on the food that the body processes.
Our first studies sought to determine whether the increase in serotonin observed in rats given a large injection of the amino acid tryptophan might also occur after rats ate meals that change tryptophan levels in the blood. We found that, immediately after the rats began to eat, parallel elevations occurred in blood tryptophan, brain tryptophan, and brain serotonin levels. These findings suggested that the production and release of serotonin in brain neurons were normally coupled with blood-tryp-tophan increases. In later studies we found that injecting insulin into a rat’s bloodstream also caused parallel elevations in blood and brain tryptophan levels and in serotonin levels. We then decided to see whether the secretion of the animal’s own insulin similarly affected serotonin production. We gave the rats a carbohydrate-containing meal that we knew would elicit insulin secretion. As we had hypothesized, the blood trypto- phan level and the concentrations of tryptophan serotonin in the brain increased after the meal.
Surprisingly, however, when we added a large amount of protein to the meal, brain tryptophan and serotonin levels fell. Since protein contains tryptophan, why should it depress brain tryptophan levels? The answer lies in the mechanism that provides blood tryp- tophan to the brain cells. This same mechanism also provides the brain cells with other amino acids found in protein, such as tyrosine and leucine. The consumption of protein increases blood con- centration of the other amino acids much more, proportionately, than it does that of tryptophan. The more protein in the meal, the lower is the ratio of the resulting blood-tryptophan concentration to the concentration of competing amino acids, and the more slowly is tryptophan provided to the brain. Thus the more protein in a meal, the less serotonin subsequently produced and re- leased. [br] According to the passage, an injection of insulin was most similar in its effect on rats to an injection of
选项
A、tyrosine.
B、leucine.
C、blood.
D、tryptophan.
E、protein.
答案
D
解析
给老鼠打一针胰岛素,相当于给它打一针:文中胰岛素、色氨酸都是促进血清素分泌的。∴D正确。色氨酸。
转载请注明原文地址:https://tihaiku.com/zcyy/3357423.html
相关试题推荐
Themetabolicrateofsharksislowcomparedwiththeratesofmostotherfishes
ThepsychologistWilliamJamesbelievedthatfacialexpressionsnotonlyprovide
Inthe1950’sastronomersweredividedbetweenthosewhobelievedtheuniverseb
Untilrecentlymostastronomersbelievedthatthespacebetweenthegalaxies
Untilrecentlymostastronomersbelievedthatthespacebetweenthegalaxies
Untilrecentlymostastronomersbelievedthatthespacebetweenthegalaxies
Untilrecentlymostastronomersbelievedthatthespacebetweenthegalaxies
Itwasoncebelievedthatthebrainwasindependentofmetabolicprocesseso
Itwasoncebelievedthatthebrainwasindependentofmetabolicprocesseso
Itwasoncebelievedthatthebrainwasindependentofmetabolicprocesseso
随机试题
Managementjargoncanalienatestaffandleavebosseslookinguntrustworthy
OldageintheUnitedStatespresentsmanyproblemsandopportunities.Asa
A.两者相同 B.2倍 C.4倍 D.8倍
中线点不直接接地系统是()。A.35kV及以下 B.35kV及以上 C.1
登革热是通过A.虫媒传播 B.接触传播 C.呼吸道飞沫传播 D.粪-口途径
关于霉变,下列选项错误的是()。A.霉变是真菌在中药表面或内部的滋生现象B.中
谈美!这话太突如其来了!在这个危急存亡的年头,我还有心肝来“谈风月”么?是的,我
在对培训成果进行评估时,调查问卷中,“您对该培训项目满意吗?”的提问属于( )
有一种学说认为,学习是个体利用智慧对情境与自身关系的顿悟。该学说的创立者是(
2018-19、根据《建设项目环境影响评价分类管理名录》,关于建设项目环境影响评
最新回复
(
0
)