In vivo binding of [125I]RTI-55 to dopamine transporters: pharmacology and regional distribution with autoradiography.
Previous studies have demonstrated that para-substituted WIN 35,065-2 analogs of cocaine show high binding affinity for dopamine uptake sites both in vitro and in vivo, and inhibit DA uptake in vitro. These analogs also produce potent cocaine-like behavioral effects in various procedures. The purpose of the present studies was to evaluate the iodinated WIN 35,065-2 analog [125I]RTI-55 as an in vivo ligand for the DA transporter. Following intravenous injection in mice, [125I]RTI-55 showed highest accumulation in areas with high densities of dopamine uptake sites. Light microscopic autoradiography was used to examine binding with higher resolution. Displacement studies demonstrated that [125I]RTI-55 binding in dopamine containing regions, striatum and olfactory tubercles, was saturable and inhibited by other cocaine analogs. GBR 12909 and WIN 35,428 significantly inhibited [125I]RTI-55 binding in striatum, while paroxetine significantly inhibited hypothalamic binding but had little effect in striatum. The latter finding suggests that [125I]RTI-55 also binds to the serotonin transporter. Haloperidol had no effect on [125I]RTI-55 binding in any brain region measured. In addition, treatment of animals with the dopamine neurotoxin MPTP caused significant reductions in striatal [125I]RTI-55 binding. The results of these studies indicate that [125I]RTI-55 binds primarily to the dopamine transporter in the mouse striatum in vivo.
Cline
E J
EJ
Neuroscience Branch, Addiction Research Center, National Institute on Drug Abuse, Baltimore, Maryland 21224.
Scheffel
U
U
Boja
J W
JW
Mitchell
W M
WM
Carroll
F I
FI
Abraham
P
P
Lewin
A H
AH
Kuhar
M J
MJ
D015632:1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine / Q000494:pharmacology; D000818:Animals; D001345:Autoradiography; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D003042:Cocaine / Q000031:analogs & derivatives* / Q000378:metabolism; D050483:Dopamine Plasma Membrane Transport Proteins; D007457:Iodine Radioisotopes; D007700:Kinetics; D008297:Male; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D051379:Mice; D008815:Mice, Inbred Strains; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009928:Organ Specificity
D002352:Carrier Proteins; D050483:Dopamine Plasma Membrane Transport Proteins; D007457:Iodine Radioisotopes; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; C069723:2beta-carbomethoxy-3beta-(4-iodophenyl)tropane; D015632:1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine; D003042:Cocaine