Silverthorn M L, Dersch C M, Baumann M H, Cadet J L, Partilla J S, Rice K C, Carroll F I, Becketts K M, Brockington A, Rothman R B
Clinical Psychopharmacology Section, IRP, NIDA, NIH, Baltimore, Maryland, USA.
J Pharmacol Exp Ther. 1995 Apr;273(1):213-22.
Earlier work characterized the binding of the high-affinity cocaine analog 3 beta-(4-125iodophenyl)-tropane-2-carboxylic acid methyl ester ([125I]RTI-55) to membranes prepared from rat caudate. That investigation demonstrated that [125I]RTI-55-labeled serotonin (5-HT) transporters in addition to dopamine (DA) transporters and resolved [125I]RTI-55 binding to 5-HT transporters into two distinct components. In the present study, we characterized [125I]RTI-55 binding to membranes prepared from whole rat brain minus caudate. The first series of experiments established that [125I]RTI-55 labels both DA and 5-HT transporters and that 50 nM paroxetine and either 1000 nM 1-[2-(diphenylmethoxy)ethyl]-4-(3-phenylpropyl)homopiperazine (LR1111) or 500 nM (RTI-120) could be used to block [125I]RTI-55 binding to the 5-HT and DA transporters, thereby generating selective assay conditions for the DA and 5-HT transporters, respectively. Selective lesioning of dopaminergic and serotonergic neurons with intracerebroventricular 6-hydroxydopamine and 5,7-dihydroxytryptamine selectively decreased [125I]RTI-55 binding to DA and 5-HT transporters, respectively, thereby confirming the selectivity of the assay conditions. The ligand-selectivity pattern of the whole brain minus caudate 5-HT transporter correlated significantly with that of the caudate 5-HT transporter, although there were some striking differences for selected test agents. Additional experiments resolved [125I]RTI-55 binding to the 5-HT transporter into two components. A ligand-selectivity analysis of the two components failed to identify a highly selective test agent. In summary, the major findings of the present study are that [125I]RTI-55 labels both DA and 5-HT transporters in membranes prepared from whole brain minus caudate, that 50 nM paroxetine and either 1000 nM LR1111 or 500 nM RTI-120 can be used as a blocking agent to generate selective assay conditions for the DA and 5-HT transporters, respectively, and that [125I]RTI-55 binding to the 5-HT transporter can be resolved into two similar components.
早期的研究对高亲和力可卡因类似物3β-(4-¹²⁵I-碘苯基)-托烷-2-羧酸甲酯([¹²⁵I]RTI-55)与大鼠尾状核制备的膜的结合进行了表征。该研究表明，[¹²⁵I]RTI-55除了标记多巴胺(DA)转运体之外，还标记5-羟色胺(5-HT)转运体，并将[¹²⁵I]RTI-55与5-HT转运体的结合解析为两个不同的组分。在本研究中，我们对[¹²⁵I]RTI-55与去除尾状核的全大鼠脑制备的膜的结合进行了表征。第一组实验确定，[¹²⁵I]RTI-55标记DA和5-HT转运体，并且50 nM帕罗西汀与1000 nM 1-[2-(二苯基甲氧基)乙基]-4-(3-苯基丙基)高哌嗪(LR1111)或500 nM(RTI-120)均可用于阻断[¹²⁵I]RTI-55与5-HT和DA转运体的结合，从而分别为DA和5-HT转运体生成选择性检测条件。用脑室注射6-羟基多巴胺和5,7-二羟基色胺对多巴胺能和5-羟色胺能神经元进行选择性损伤，分别选择性降低[¹²⁵I]RTI-55与DA和5-HT转运体的结合，从而证实了检测条件的选择性。去除尾状核的全脑5-HT转运体的配体选择性模式与尾状核5-HT转运体的配体选择性模式显著相关，尽管对于某些选定的测试药物存在一些显著差异。额外的实验将[¹²⁵I]RTI-55与5-HT转运体的结合解析为两个组分。对这两个组分的配体选择性分析未能鉴定出一种高度选择性的测试药物。总之，本研究的主要发现是，[¹²⁵I]RTI-55标记去除尾状核的全脑制备的膜中的DA和5-HT转运体，50 nM帕罗西汀与1000 nM LR1111或500 nM RTI-120均可分别用作阻断剂，为DA和5-HT转运体生成选择性检测条件，并且[¹²⁵I]RTI-55与5-HT转运体的结合可解析为两个相似的组分。
