title: N1-methyl-2-125I-lysergic acid diethylamide, a preferred ligand for in vitro and in vivo characterization of serotonin receptors.
abstract: Methylation of 2-125I-lysergic acid diethylamide (125I-LSD) at the N1 position produces a new derivative, N1-methyl-2-125I-lysergic acid diethylamide (125I-MIL), with improved selectivity and higher affinity for serotonin 5-HT2 receptors. In rat frontal cortex homogenates, specific binding of 125I-MIL represents 80-90% of total binding, and the apparent dissociation constant (KD) for serotonin 5-HT2 receptors is 0.14 nM (using 2 mg of tissue/ml). 125I-MIL also displays a high affinity for serotonin 5-HT1C receptors, with an apparent dissociation constant of 0.41 nM at this site. 125I-MIL exhibits at least 60-fold higher affinity for serotonin 5-HT2 receptors than for other classes of neurotransmitter receptors, with the dopamine D2 receptor as its most potent secondary binding site. Studies of the association and dissociation kinetics of 125I-MIL reveal a strong temperature dependence, with very slow association and dissociation rates at 0 degree C. Autoradiographic experiments confirm the improved specificity of 125I-MIL. Selective labeling of serotonin receptors was observed in all brain areas examined. In vivo binding studies in mice indicate that 125I-MIL is the best serotonin receptor label yet described, with the highest frontal cortex to cerebellum ratio of any serotonergic radioligand. 125I-MIL is a promising ligand for both in vitro and in vivo labeling of serotonin receptors in the mammalian brain.
mesh_terms: D000818:Animals; D001345:Autoradiography; D001921:Brain / Q000378:metabolism*; D002540:Cerebral Cortex / Q000378:metabolism; D003342:Corpus Striatum / Q000378:metabolism; D005625:Frontal Lobe / Q000378:metabolism; D007457:Iodine Radioisotopes; D007700:Kinetics; D008238:Lysergic Acid Diethylamide / Q000031:analogs & derivatives* / Q000378:metabolism; D051381:Rats; D013696:Temperature
chemical_list: D007457:Iodine Radioisotopes; D008238:Lysergic Acid Diethylamide; C045599:N(1)-methyl-2-iodo-lysergic acid diethylamide