Appel N M, Mitchell W M, Garlick R K, Glennon R A, Teitler M, De Souza E B
Laboratory of Neurobiology, National Institute on Drug Abuse Addiction Research Center, Baltimore, Maryland.
J Pharmacol Exp Ther. 1990 Nov;255(2):843-57.
The 5-HT2 (serotonin) receptor has traditionally been labeled with antagonist radioligands such as [3H]ketanserin and [3H]spiperone, which label both agonist high-affinity (guanyl nucleotide-sensitive) and agonist low-affinity (guanyl nucleotide-insensitive) states of this receptor. The hallucinogen 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) is an agonist which labels the high-affinity guanyl nucleotide-sensitive state of brain 5-HT2 receptors selectively. In the present study, conditions for autoradiographic visualization of (+/-)-[125I]DOI-labeled 5-HT2 receptors were optimized and binding to slide-mounted sections was characterized with respect to pharmacology, guanyl nucleotide sensitivity and anatomical distribution. In slide-mounted rat brain sections (+/-)-[125I]DOI binding was saturable, of high affinity (KD approximately 4 nM) and displayed a pharmacologic profile typical of 5-HT2 receptors. Consistent with coupling of 5-HT2 receptors in the high-affinity state to a guanyl nucleotide regulatory protein, [125I]DOI binding was inhibited by guanyl nucleotides but not by adenosine triphosphate. Patterns of autoradiographic distribution of [125I]DOI binding to 5-HT2 receptors were similar to those seen with [3H]ketanserin- and [125I]-lysergic acid diethylamide-labeled 5-HT2 receptors. However, the density of 5-HT2 receptors labeled by the agonist [125I]DOI was markedly lower (30-50%) than that labeled by the antagonist [3H]ketanserin. High densities of [125I]DOI labeling were present in olfactory bulb, anterior regions of cerebral cortex (layer IV), claustrum, caudate putamen, globus pallidus, ventral pallidum, islands of Calleja, mammillary nuclei and inferior olive. Binding in hippocampus, thalamus and hypothalamus was generally sparse. Of note, choroid plexus, a site rich in 5-HT1c receptors had a high density of [125I]DOI binding sites but [3H]ketanserin binding in this region was low. Studies in which [125I]DOI binding to 5-HT2 receptors was blocked with spiperone revealed persisting robust [125I]DOI binding in choroid plexus, which was guanyl nucleotide-sensitive and displayed a pharmacologic profile consistent with its binding to 5-HT1c receptors. These studies suggest that [125I]DOI may be useful as a radiolabel for visualizing the agonist high-affinity state of 5-HT2 receptors and for visualizing 5-HT1c receptors.
5-羟色胺2（5-HT2，血清素）受体传统上是用拮抗剂放射性配体标记的，如[3H]酮色林和[3H]螺哌隆，这些配体可标记该受体的激动剂高亲和力（对鸟苷核苷酸敏感）和激动剂低亲和力（对鸟苷核苷酸不敏感）状态。致幻剂1-（2,5-二甲氧基-4-碘苯基）-2-氨基丙烷（DOI）是一种激动剂，可选择性标记脑5-HT2受体的高亲和力鸟苷核苷酸敏感状态。在本研究中，优化了放射自显影可视化（±）-[125I]DOI标记的5-HT2受体的条件，并从药理学、鸟苷核苷酸敏感性和解剖分布方面对其与载玻片上切片的结合进行了表征。在载玻片上的大鼠脑切片中，（±）-[125I]DOI结合是可饱和的，具有高亲和力（KD约为4 nM），并显示出5-HT2受体典型的药理学特征。与5-HT2受体在高亲和力状态下与鸟苷核苷酸调节蛋白偶联一致，[125I]DOI结合受到鸟苷核苷酸的抑制，但不受三磷酸腺苷的抑制。[125I]DOI与5-HT2受体结合的放射自显影分布模式与用[3H]酮色林和[125I]-麦角酸二乙胺标记的5-HT2受体的模式相似。然而，激动剂[125I]DOI标记的5-HT2受体密度明显低于拮抗剂[3H]酮色林标记的密度（低30-50%）。[125I]DOI标记高密度出现在嗅球、大脑皮质前部区域（IV层）、屏状核、尾状壳核、苍白球、腹侧苍白球、卡耶哈岛、乳头体核和下橄榄核。海马体、丘脑和下丘脑的结合通常很稀疏。值得注意的是，富含5-HT1c受体的脉络丛有高密度的[125I]DOI结合位点，但该区域的[3H]酮色林结合较低。用螺哌隆阻断[125I]DOI与5-HT2受体结合的研究表明，脉络丛中仍存在强烈的[125I]DOI结合，该结合对鸟苷核苷酸敏感，并显示出与其与5-HT1c受体结合一致的药理学特征。这些研究表明，[125I]DOI可能作为一种放射性标记物，用于可视化5-HT2受体的激动剂高亲和力状态以及可视化5-HT1c受体。
