Arai R, Karasawa N, Nagatsu T, Nagatsu I
Department of Anatomy, Fujita Health University School of Medicine, Aichi, Japan.
Brain Res. 1995 Jan 9;669(1):145-9. doi: 10.1016/0006-8993(94)01259-k.
The aim of the present study is to examine by immunohistochemistry whether exogenous L-5-hydroxytryptophan (L-5HTP) is decarboxylated in neurons of the substantia nigra pars compacta (SNC) and locus coeruleus (LC) of the rat. In normal rats, neurons of the SNC and LC stained intensely for aromatic L-amino acid decarboxylase (AADC). No serotonin (5HT)-positive cells were found in the two regions of the normal rats. In rats that were intraperitoneally injected with L-5HTP alone, the SNC neurons stained deeply for 5HT, but the LC neurons showed only a faint staining for 5HT. In rats that intraperitoneally received both a monoamine oxidase (MAO) inhibitor and L-5HTP, when compared with the L-5HTP-injected rats, the LC neurons became much darker in 5HT staining, but the SNC neurons showed only a slight increase in 5HT staining. The present findings suggest that (i) AADC in dopaminergic neurons of the SNC and in noradrenergic neurons of the LC can catalyze the in vivo decarboxylation of exogenous L-5HTP to produce 5HT, and (ii) most of the newly produced 5HT in the LC neurons is rapidly degraded by endogenous MAO.
本研究的目的是通过免疫组织化学检查外源性L-5-羟色氨酸（L-5HTP）在大鼠黑质致密部（SNC）和蓝斑（LC）神经元中是否脱羧。在正常大鼠中，SNC和LC的神经元对芳香族L-氨基酸脱羧酶（AADC）染色强烈。在正常大鼠的这两个区域未发现5-羟色胺（5HT）阳性细胞。在仅腹腔注射L-5HTP的大鼠中，SNC神经元对5HT染色深，但LC神经元对5HT仅显示微弱染色。在腹腔同时接受单胺氧化酶（MAO）抑制剂和L-5HTP的大鼠中，与注射L-5HTP的大鼠相比，LC神经元的5HT染色变得深得多，但SNC神经元的5HT染色仅略有增加。本研究结果表明：（i）SNC多巴胺能神经元和LC去甲肾上腺素能神经元中的AADC可催化外源性L-5HTP在体内脱羧生成5HT；（ii）LC神经元中大多数新生成的5HT被内源性MAO迅速降解。
