Sequential versus nonsequential measurement of density and affinity of dopamine D2 receptors with [11C]raclopride: effect of methamphetamine.
The multiple ligand concentration assays (MLCRA) method provides researchers with the ability to measure in vivo receptor characteristics in a stable condition. Measurements of the density and affinity of the dopamine D2 receptors with [11C]raclopride, using a sequential method (three scans throughout 1 day) or a nonsequential method (three scans spread over several weeks but at the same time of the day), yield similar values. However, after an acute challenge with drugs that affect dopamine neurotransmission, the concentration of endogenous ligand may vary over the course of the in vivo sequential MLCRA. Combined PET-microdialysis studies after acute amphetamine showed that during the imaging time frame the concentrations of extracellular dopamine vary widely, but that nonetheless the decrease in raclopride binding potential is sustained and nearly constant over time. These observations apparently contradict the simple competitive displacement model if the changes in extracellular concentration are taken to reflect necessarily comparable changes at the binding sites. To understand the effect of the delay between drug administration and start-to-end of data acquisition on the MLCRA results, we compared the outcomes of the sequential and nonsequential methods after methamphetamine. Comparison of the binding potential, density, and affinity of D2 receptors in both experimental conditions revealed good concordance between the data sets, suggesting that methamphetamine produces sustained and stable increases in synaptic dopamine.
Doudet
Doris J
DJ
Department of Medicine, Division of Neurology and TRIUMF, University of British Columbia, Vancouver, BC, Canada. ddoudet@interchange.ubc.ca
Holden
James E
JE
D000818:Animals; D001921:Brain / Q000000981:diagnostic imaging / Q000187:drug effects / Q000378:metabolism; D002250:Carbon Radioisotopes; D018492:Dopamine Antagonists; D018765:Dopamine Uptake Inhibitors / Q000494:pharmacology*; D008253:Macaca mulatta; D008297:Male; D008694:Methamphetamine / Q000494:pharmacology*; D020891:Raclopride; D011877:Radionuclide Imaging; D017448:Receptors, Dopamine D2 / Q000378:metabolism*; D009435:Synaptic Transmission / Q000187:drug effects
D002250:Carbon Radioisotopes; D018492:Dopamine Antagonists; D018765:Dopamine Uptake Inhibitors; D017448:Receptors, Dopamine D2; D020891:Raclopride; D008694:Methamphetamine