Hervé D, Trovero F, Blanc G, Glowinski J, Tassin J P
Chaire de Neuropharmacologie, INSERM U.114, Collège de France, Paris.
Neuroscience. 1992;46(3):687-700. doi: 10.1016/0306-4522(92)90155-u.
On the basis of experiments made on striatal membranes, Leff and Creese [Molec. Pharmac. (1985) 27, 184-192] have proposed that tritiated dopamine binds to a high-affinity agonist state of D1 dopamine receptors (D1h) which adopt this conformation when they are associated with the GTP-binding protein involved in the transduction process. Quantitative autoradiography was thus used to look for the distribution of these D1h sites in the rat brain and to compare it with that of D1 receptors labelled with [3H]7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benz aze pine [( 3H]SCH23390), a D1 antagonist. The effects of unilateral 6-hydroxydopamine lesion of the ascending dopamine pathways on the density of [3H]dopamine D1h and [3H]SCH23390 binding sites in the striatum and the nucleus accumbens were also analysed. In the striatum, when D2 receptors were blocked by spiroperidol (20 nM), [3H]dopamine was found to bind specifically to dopamine receptors of the D1 type. Complementary experiments made with dopamine uptake blockers indicated that high-affinity dopamine uptake sites were not labelled by [3H]dopamine under our experimental conditions. The anatomical distribution of [3H]dopamine D1h binding sites was found to be markedly different from that of [3H]SCH23390 binding sites. This was particularly the case in the substantia nigra, some amygdaloid nuclei and the prefrontal cortex--structures in which the ratios between [3H]SCH23390 and [3H]dopamine binding sites were more than seven-fold higher than that observed in the striatum. [3H]SCH23390 binding was not significantly affected in either the striatum or the nucleus accumbens six weeks after a complete unilateral destruction of ascending dopamine pathways. In contrast, a marked decrease in [3H]dopamine D1h binding sites was found in both structures, but this effect was lower in the medioventral (-60%) than in the laterodorsal (-81%) part of the striatum, even though dopamine denervation was uniform throughout the structure. Preincubation of the sections with dopamine (0.5 microM) led to a partial recovery (+126%) in the lesioned striatum and an increase of [3H]dopamine labelling in the control striatum (+68%). This suggest that the presence of dopamine stabilizes the D1h state of D1 receptors. The absence or low amount of dopamine, either due to dopamine denervation or naturally occurring (prefrontal cortex), would then impair the [3H]dopamine D1h binding. In addition, a lower coupling of D1 receptors with adenylate cyclase was observed in the substantia nigra when compared to that in the striatum: this may explain the relatively weak [3H]dopamine binding in the substantia nigra.(ABSTRACT TRUNCATED AT 400 WORDS)
基于对纹状体膜进行的实验，莱夫和克里兹[《分子药理学》（1985年）27卷，第184 - 192页]提出，氚标记的多巴胺与D1多巴胺受体的高亲和力激动剂状态（D1h）结合，当这些受体与参与转导过程的GTP结合蛋白结合时会呈现这种构象。因此，采用定量放射自显影法来寻找这些D1h位点在大鼠脑中的分布，并将其与用[3H]7 - 氯 - 8 - 羟基 - 3 - 甲基 - 1 - 苯基 - 2,3,4,5 - 四氢 - 1H - 3 - 苯并氮杂卓[（3H）SCH23390]标记的D1受体的分布进行比较，[（3H）SCH23390]是一种D1拮抗剂。还分析了多巴胺上行通路单侧6 - 羟基多巴胺损伤对纹状体和伏隔核中[3H]多巴胺D1h和[3H]SCH23390结合位点密度的影响。在纹状体中，当D2受体被螺哌啶醇（20 nM）阻断时，发现[3H]多巴胺特异性结合于D1型多巴胺受体。用多巴胺摄取阻滞剂进行的补充实验表明，在我们的实验条件下，高亲和力多巴胺摄取位点未被[3H]多巴胺标记。发现[3H]多巴胺D1h结合位点的解剖分布与[3H]SCH23390结合位点的分布明显不同。在黑质、一些杏仁核和前额叶皮质中尤其如此，在这些结构中，[3H]SCH23390与[3H]多巴胺结合位点的比率比在纹状体中观察到的高出七倍以上。在多巴胺上行通路完全单侧破坏六周后，纹状体或伏隔核中的[3H]SCH23390结合没有受到显著影响。相比之下，在这两个结构中均发现[3H]多巴胺D1h结合位点明显减少，但这种效应在纹状体的内侧腹侧（ - 60%）比外侧背侧（ - 81%）部分更低，尽管多巴胺去神经支配在整个结构中是均匀的。将切片用多巴胺（0.5 microM）预孵育导致损伤纹状体部分恢复（ + 126%），对照纹状体中[3H]多巴胺标记增加（ + 68%）。这表明多巴胺的存在稳定了D1受体的D1h状态。由于多巴胺去神经支配或自然存在（前额叶皮质）导致的多巴胺缺失或含量低，会损害[3H]多巴胺D1h结合。此外，与纹状体相比，在黑质中观察到D1受体与腺苷酸环化酶的偶联较低：这可能解释了黑质中相对较弱的[3H]多巴胺结合。（摘要截断于400字）
