Daniel P M, Moorhouse S R, Pratt O E
Psychol Med. 1976 May;6(2):277-86. doi: 10.1017/s0033291700013830.
There is evidence that changes in the concentrations of the monoamine neurotransmitters within the brain are associated with changes in mental processes, with disorders of control of movement and with certain neuropsychiatric diseases. These neurotransmitters are synthesized in the brain from aromatic amino acid precursors that have to be obtained from the circulating blood. In this study some factors which alter the rates of entry of four amino acids (the important neurotransmitter precursors L-tyrosine and L-tryptophan, as well as L-phenylalanine and L-histidine) into the brain have been studied and the findings considered in relation to conditions in which the quantities of one or more of the monoamine neurotransmitters formed within the cerebral cells may be either too large or too small. Thus too little neurotransmitter will be formed if competition between amino acids for the carriers transporting them into the cerebral cells causes the exclusion of a large proportion of any of the aromatic amino acid precursors from the brain. ,or example, L-tryptophan is partially excluded from the brain if a raised level of any one of several other amino acids is maintained in the circulation. Of these, L-phenylalanine inhibits the transport of L-tryptophan into the brain most effectively, while aromatic amino acids in general exclude L-tryptophan more effectively than do other neutral amino acids. Over-production of one or more of the monoamine neurotransmitters is likely to occur when there is too much of one of the aromatic amino acid precursors in the brain cells as a result of abnormally high uptake from the blood, or as a result of their release by an excessive breakdown of the protein within these cells. Underproduction of neurotransmitters may occur in certain disease states, such as some aminoacidurias or Parkinsonism. We have listed some conditions associated with altered mental states or motor disability in which over- or under-production of monoamine neurotransmitters may occur and have tried to relate the findings in human disease with our experimental results.
有证据表明，大脑中单胺类神经递质浓度的变化与心理过程的改变、运动控制障碍以及某些神经精神疾病有关。这些神经递质在大脑中由必须从循环血液中获取的芳香族氨基酸前体合成。在本研究中，已经研究了一些改变四种氨基酸（重要的神经递质前体L-酪氨酸和L-色氨酸，以及L-苯丙氨酸和L-组氨酸）进入大脑速率的因素，并结合脑细胞内形成的一种或多种单胺类神经递质数量可能过多或过少的情况来考虑这些发现。因此，如果氨基酸之间对将它们转运到脑细胞中的载体的竞争导致大脑中任何一种芳香族氨基酸前体的很大一部分被排除，那么形成的神经递质就会太少。例如，如果循环中几种其他氨基酸中的任何一种水平升高，L-色氨酸就会部分被排除在大脑之外。其中，L-苯丙氨酸最有效地抑制L-色氨酸进入大脑，而一般来说，芳香族氨基酸比其他中性氨基酸更有效地排除L-色氨酸。当由于从血液中异常高摄取或由于这些细胞内蛋白质过度分解导致其释放，使得脑细胞中一种或多种芳香族氨基酸前体过多时，可能会发生一种或多种单胺类神经递质的过度产生。神经递质产生不足可能发生在某些疾病状态下，如一些氨基酸尿症或帕金森病。我们列出了一些与精神状态改变或运动障碍相关的情况，其中可能发生单胺类神经递质的过度或不足产生，并试图将人类疾病的发现与我们的实验结果联系起来。
