Iodine-123-labelled 3beta-(4-iodophenyl)tropane-2beta-carboxylic acid ([123I]beta-CIT) labels both the dopamine transporter (DAT) and the serotonin transporter (5-HTT) and this ligand is able to clarify pathological changes in both dopaminergic and serotonergic systems. However, the differential kinetics of beta-CIT binding to DAT and 5-HTT has not been clarified fully. In this study we examined time-activity curves of [123I]beta-CIT in individual regions in the rat brain. Using cerebellum as the reference region, k3 and k4 values were estimated by a two-compartment kinetic analysis. In the striatum, the kinetics was slowest among all brain areas. In this area specific binding reached its peak 4 h after the injection. In the hypothalamus, specific binding reached its peak 1 h after the injection and its amount did not change until 4 h after the injection. In the occipital cortex, the binding and washout of the ligand were fastest among all brain regions. Estimated k3 values were 0.040+/-0.003 in the striatum, 0.019+/-0.002 in the hypothalamus and 0.082+/-0.011 in the occipital cortex (min-1, mean +/-SD). Estimated k4 values were 0.0034+/-0.0005 in the striatum, 0.0071+/-0.0009 in the hypothalamus and 0.083+/-0.013 in the occipital cortex (min-1, mean +/-SD). Therefore binding kinetics of [123i]beta-cit in the region rich in dat is apparently different from that in the region rich in 5-HTT. These results will provide fundamental data to image both DAT and 5-HTT in one series of examinations with [123I]beta-CIT.
A novel monoclonal antibody (ASH1a/256C) that recognizes atherosclerotic lesions in human and Watanabe heritable hyperlipidemic (WHHL) rabbit aortae is described. When 123 I-labeled ASH1a/256C antibody is injected intravenously into WHHL rabbits, it associates specifically with fatty streaks on the aorta. The antigen recognized by the antibody is lipid, based on extraction with chloroform and methanol from WHHL rabbit tissues. The antigen, purified by high performance liquid chromatography, was shown to be phosphatidylcholine (PC), which contains unsaturated fatty acyl groups based on analyses utilizing 1 H and 13 C nuclear magnetic resonance, Fourier transfer-infrared spectrum, and mass spectrometry. The antibody did not react with other classes of phospholipids or neutral lipids when tested using an enzyme-linked immunosorbent assay. When PC was mixed with either cholesterol, cholesteryl ester, or triacylglycerol, however, the reactivity of the antibody to PC increased up to 8-fold. Homogenates of aorta tissue obtained from normal and WHHL rabbits were fractionated using sucrose density gradient ultracentrifugation in which neutral lipid droplets, cellular membranes, and proteins are separated. The phospholipid content in cellular membrane fractions from WHHL rabbits was twice as high as that of normal rabbits, and there was an enormous difference in the antigenic activity in these fractions. The content of cholesterol in the cellular membrane fraction of WHHL rabbits was approximately 50 times higher than that of normal rabbits. Addition of neutral lipids to the cellular membrane fraction of normal rabbit markedly increased the antigenic activity. Atheromatous lesions in thickened WHHL rabbit aortic intima that were rich in lipid droplets were stained positively with ASH1a/256C immunohistochemically. These results strongly suggest that PC-neutral lipid complex domains are formed in atherosclerotic lesions.
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