Basic research on neuroreceptor mapping of cholinergic system using nuclear medicine imaging

对脑胆碱能神经支配的核医学成像进行了基础性研究。通过在单侧基底前脑制造伊博藤酸损伤，实验制备了胆碱能去神经支配模型。为了评估被动回避在新反应习得和长时间记忆方面的表现，研制了一种高精度的步进测试装置。使用专用图像处理系统进行体外定量受体放射自显影，以寻找有希望的配体来绘制大脑胆碱能神经支配。在模型的同侧和对侧部位，总毒蕈碱乙酰胆碱受体、M_1和M_2在皮质中均无显著差异。同时用^3H-2-（4-苯基胡椒碱）环己醇（AH5183）绘制突触前胆碱能神经分布图。与模型中对侧部位相比，AH5183的结合在同侧部位的皮质中平均下降了14%，具有统计学意义。这些结果可能暗示AH5183是一个敏感的突触前乙酰胆碱水平标记。为了开发一种新的SPECT配体，合成了n -异丙基-对碘安非他明（IMP）的类似物n -对碘苯乙基二氨基二硫醇（DADT-IPE），并以氯化亚锡为还原剂与^<99m>Tc络合。用高效液相色谱法从^<99m>Tc-DADT-IPE中分离出两个配合物a和b。竞争抑制研究表明，DADT-IPE的IC_<50>值与IMP相似。其中一种复合物[^<99m>Tc-DADT-IPE(a)]在大鼠体内的生物分布研究表明，该示踪剂在静脉注射后5分钟仍有0.65%的注射剂量留在脑内，在注射后60分钟仍有0.53%的剂量留在脑内。而另一复合物[^<99m>Tc-DADT-IPE(b)]在注射后5分钟的脑内对应剂量为0.34%，在注射后60分钟的脑内对应剂量为0.28%。从大鼠脑中清除^<99m>Tc-DADT-IPE(a)的半衰期大于5h。这些结果表明^<99m>Tc-DADT-IPE(a)具有适合脑灌注成像的特征。采用原位杂交技术，利用寡核苷酸DNA探针对毒毒碱乙酰胆碱受体信使RNA基因表达进行成像。少

A fundamental study was performed on the nuclear medicine imaging of cholinergic innervation in the brain. A cholinergic denervation model was experimentally prepared by producing an ibotenic acid lesion in the unilateral basal forebrain. To assess the passive avoidance performance in terms of acquisition of new responses and long term retention, a step-through apparatus with high precision was newly developed. In-vitro quantitative receptor autoradiography was performed to look for a promising ligand for mapping cholinergic innervation in the brain using a dedicated image processing system. No significant differences were observed in total,M_1, and M_2 muscarinic acetylcholine receptors in the cortices between the ipsilateral and contralateral sites in the model. Simultaneously mapping of presynaptic cholinergic innervation was carried out using ^3H-2-(4-phenylpiperidino)cyclohexanol (AH5183). Statistically significant 14% decrease of AH5183 binding on an average was demonstrated in t … More he cortices of the ipsilateral site, relative to the contralateral site in models. These results may imply that AH5183 is a sensitive presynaptic marker of acetylcholine levels. To develop a new useful ligand for SPECT, an N-p-iodophenethyl diaminodithiol (DADT-IPE), an analog of N-isopropyl-p-iodoamphetamine(IMP), was synthesized and subsequently complexioned with ^<99m>Tc,using stannous chloride as a reducing agent. Two complexes (a and b) were separated from ^<99m>Tc-DADT-IPE by HPLC. Competitive inhibition studies showed that the IC_<50> value of DADT-IPE was similar to that of IMP. Biodistribution studies of one of the complexes [^<99m>Tc-DADT-IPE(a)] in rats show that 0.65% of the injected dose of the tracer remained in the brain at 5 min after intravenous injection, with 0.53% of the dose remaining in the brain at 60 min post-injection, whereas the corresponding values for the other complex [^<99m>Tc-DADT-IPE(b)] were 0.34% dose in the brain at 5 min and 0.28% dose in the brain 60 min post-injection. The half-life for clearance of ^<99m>Tc-DADT-IPE(a) from rat brain was found to be more than 5h. These results suggest that ^<99m>Tc-DADT-IPE(a) has characteristics which are suitable for cerebral perfusion imaging. Moreover in-situ hybridization technique was applied to this model for imaging of gene expression of messenger RNA for muscarinic acetylcholine receptors using oligonucleotide DNA probes. Less