title: Cocaine occupancy of sigma1 receptors and dopamine transporters in mice.
abstract: Activation of sigma1 (σ1) receptors contributes to the behavioral and toxic effects of (-)-cocaine. We studied a key step, the ability of (-)-cocaine to occupy σ1 receptors in vivo, using CD-1(®) mice and the novel radioligand [(125) I]E-N-1-(3'-iodoallyl)-N'-4-(3",4"-dimethoxyphenethyl)-piperazine ([(125) I]E-IA-DM-PE-PIPZE). (-)-Cocaine displayed an ED50 of 68 μmol/kg for inhibition of specific radioligand binding in whole brain, with values between 73 and 80 μmol/kg for heart, lung, and spleen. For comparison, an ED50 of 26 μmol/kg for (-)-cocaine occupancy of striatal dopamine transporters (DAT) was determined by inhibition of [(125) I]3β-(4-iodophenyl)tropan-2β-carboxylic acid isopropyl ester ([(125) I]RTI-121) binding. A chief finding is the relatively small potency difference between (-)-cocaine occupancy of σ1 receptors and the DAT, although the DAT occupancy is likely underestimated. Interactions of (-)-cocaine with σ1 receptors were assessed further using [(125) I]E-IA-DM-PE-PIPZE for regional cerebral biodistribution studies and quantitative ex vivo autoradiography of brain sections. (-)-Cocaine binding to cerebral σ1 receptors proved directly proportional to the relative site densities known for the brain regions. Nonradioactive E-IA-DM-PE-PIPZE gave an ED50 of 0.23 μmol/kg for occupancy of cerebral σ1 receptors, and a 3.16 μmol/kg (i.p.) dose attenuated (-)-cocaine-induced locomotor hyperactivity by 30%. This effect did not reach statistical significance, but suggests that E-IA-DM-PE-PIPZE is a probable σ1 receptor antagonist. As groundwork for the in vivo studies, we used standard techniques in vitro to determine ligand affinities, site densities, and pharmacological profiles for the σ1 and σ2 receptors expressed in CD-1(®) mouse brain.
authors.affiliation: Department of Radiology and Radiopharmaceutical Sciences Institute, University of Missouri, Missouri, 65211, Columbia.|Research Service, Harry S. Truman Memorial Veterans' Hospital, Missouri, 65201, Columbia.
authors.forename: John R
authors.initials: JR
authors.lastname: Lever
authors.affiliation: Department of Radiology and Radiopharmaceutical Sciences Institute, University of Missouri, Missouri, 65211, Columbia.|Research Service, Harry S. Truman Memorial Veterans' Hospital, Missouri, 65201, Columbia.
authors.forename: Emily A
authors.initials: EA
authors.lastname: Fergason-Cantrell
authors.affiliation: Department of Radiology and Radiopharmaceutical Sciences Institute, University of Missouri, Missouri, 65211, Columbia.|Research Service, Harry S. Truman Memorial Veterans' Hospital, Missouri, 65201, Columbia.
authors.forename: Lisa D
authors.initials: LD
authors.lastname: Watkinson
authors.affiliation: Department of Radiology and Radiopharmaceutical Sciences Institute, University of Missouri, Missouri, 65211, Columbia.|Research Service, Harry S. Truman Memorial Veterans' Hospital, Missouri, 65201, Columbia.
authors.forename: Terry L
authors.initials: TL
authors.lastname: Carmack
authors.affiliation: Department of Radiology and Radiopharmaceutical Sciences Institute, University of Missouri, Missouri, 65211, Columbia.|Research Service, Harry S. Truman Memorial Veterans' Hospital, Missouri, 65201, Columbia.
authors.forename: Sarah A
authors.initials: SA
authors.lastname: Lord
authors.affiliation: Department of Chemistry, University of Missouri, Missouri, 65211, Columbia.
authors.forename: Rong
authors.initials: R
authors.lastname: Xu
authors.affiliation: Department of Psychological Sciences, University of Missouri, Missouri, 65211, Columbia.|Center for Translational Neuroscience, University of Missouri, Missouri, 65211, Columbia.
authors.forename: Dennis K
authors.initials: DK
authors.lastname: Miller
authors.affiliation: Department of Chemistry, University of Missouri, Missouri, 65211, Columbia.|MU Research Reactor Center, University of Missouri, Missouri, 65212, Columbia.
authors.forename: Susan Z
authors.initials: SZ
authors.lastname: Lever
mesh_terms: D000818:Animals; D001345:Autoradiography; D001667:Binding, Competitive; D001921:Brain / Q000187:drug effects* / Q000378:metabolism*; D003042:Cocaine / Q000493:pharmacokinetics / Q000494:pharmacology*; D050483:Dopamine Plasma Membrane Transport Proteins / Q000378:metabolism*; D018765:Dopamine Uptake Inhibitors / Q000493:pharmacokinetics / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D008297:Male; D051379:Mice; D009043:Motor Activity / Q000187:drug effects; D017480:Receptors, sigma / Q000378:metabolism*; D000097605:Sigma-1 Receptor
chemical_list: D003042:Cocaine; D050483:Dopamine Plasma Membrane Transport Proteins; D018765:Dopamine Uptake Inhibitors; D017480:Receptors, sigma; D000097605:Sigma-1 Receptor
keywords: cocaine; dopamine transporter; locomotor activity; mouse; occupancy; sigma receptor; substance abuse