Diksic M
Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, 3801 University St., Montreal, QC H3A 2B4.
J Psychiatry Neurosci. 2001 Sep;26(4):293-303.
The alpha-methyl-L-trypotophan (alpha-MTrp) method for the study of the brain serotonergic system is based on the fact that labelled alpha-MTrp is taken up by and, in part, retained in the brain, and this retention (trapping) is proportional to brain serotonin (5-HT) synthesis. A 3-compartment model is proposed in which the plasma, the precursor and irreversible pools are mathematically distinct compartments. The irreversible compartment is assumed to be the one in which the tracer is trapped. By definition, the tracer from the irreversible compartment does not exchange directly with the plasma compartment. The rate at which labelled alpha-MTrp is trapped is converted to the rate of 5-HT synthesis by dividing it by a conversion factor, called the lumped constant, and multiplying it by the plasma-free tryptophan concentration. Our results revealed that brain 5-HT synthesis can be influenced by the extraneuronal concentration of 5-HT and that, generally, the influence is not uniform throughout the brain. They also suggest that brain trapping of labelled alpha-MTrp relates to 5-HT synthesis. The proposed procedure for converting the rate at which labelled alpha-MTrp is trapped to brain 5-HT synthesis rates is based on measurements that suggest that plasma-free Trp relates to brain 5-HT synthesis. However, as with all biological models, there is likely room for improvement in our approach.
用于研究脑血清素能系统的α-甲基-L-色氨酸（α-MTrp）方法基于以下事实：标记的α-MTrp被脑摄取并部分保留在脑中，且这种保留（捕获）与脑血清素（5-羟色胺，5-HT）合成成正比。提出了一个三室模型，其中血浆、前体和不可逆池在数学上是不同的隔室。假定不可逆隔室是示踪剂被捕获的隔室。根据定义，来自不可逆隔室的示踪剂不与血浆隔室直接交换。通过将标记的α-MTrp被捕获的速率除以一个称为总常数的转换因子，并乘以无血浆色氨酸浓度，可将其转换为5-HT合成速率。我们的结果表明，脑5-HT合成可受5-HT的神经外浓度影响，而且一般来说，这种影响在整个脑中并不均匀。结果还表明，标记的α-MTrp在脑中的捕获与5-HT合成有关。将标记的α-MTrp被捕获的速率转换为脑5-HT合成速率的建议程序基于一些测量结果，这些结果表明无血浆色氨酸与脑5-HT合成有关。然而，与所有生物学模型一样，我们的方法可能仍有改进空间。
