Relationship between psychostimulant-induced "high" and dopamine transporter occupancy.
The ability of cocaine to inhibit the dopamine transporter (DAT) appears to be crucial for its reinforcing properties. The potential use of drugs that produce long-lasting inhibition of the DAT as a mean of preventing the "high" and reducing drug-seeking behavior has become a major strategy in medication development. However, neither the relation between the high and DAT inhibition nor the ability to block the high by prior DAT blockade have ever been demonstrated. To evaluate if DAT could prevent the high induced by methylphenidate (MP), a drug which like cocaine inhibits the DAT, we compared the responses in eight non-drug-abusing subjects between the first and the second of two MP doses (0.375 mg/kg, i.v.) given 60 min apart. At 60 min the high from MP has returned to baseline, but 75-80% of the drug remains in brain. Positron-emission tomography and [11C]d-threo-MP were used to estimate DAT occupancies at different times after MP. DAT inhibition by MP did not block or attenuate the high from a second dose of MP given 60 min later, despite a 80% residual transporter occupancy from the first dose. Furthermore some subjects did not perceive a high after single or repeated administration despite significant DAT blockade. These results indicate that DAT occupancy is not sufficient to account for the high, and that for DAT inhibitors to be therapeutically effective, occupancies > 80% may be required.
Volkow
N D
ND
Medical Department, Brookhaven National Laboratory, Upton, NY 11973, USA.
Wang
G J
GJ
Fowler
J S
JS
Gatley
S J
SJ
Ding
Y S
YS
Logan
J
J
Dewey
S L
SL
Hitzemann
R
R
Lieberman
J
J
D000328:Adult; D001007:Anxiety; D001794:Blood Pressure / Q000187:drug effects; D001921:Brain / Q000000981:diagnostic imaging / Q000187:drug effects / Q000502:physiology*; D002250:Carbon Radioisotopes; D002352:Carrier Proteins / Q000187:drug effects / Q000378:metabolism*; D000697:Central Nervous System Stimulants / Q000493:pharmacokinetics / Q000494:pharmacology*; D002531:Cerebellum / Q000000981:diagnostic imaging / Q000187:drug effects / Q000502:physiology; D003342:Corpus Striatum / Q000000981:diagnostic imaging / Q000187:drug effects / Q000502:physiology; D050483:Dopamine Plasma Membrane Transport Proteins; D018765:Dopamine Uptake Inhibitors / Q000493:pharmacokinetics / Q000494:pharmacology*; D004644:Emotions / Q000187:drug effects* / Q000502:physiology; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D007700:Kinetics; D008297:Male; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D008774:Methylphenidate / Q000493:pharmacokinetics* / Q000494:pharmacology*; D009419:Nerve Tissue Proteins; D013997:Time Factors; D014018:Tissue Distribution; D014055:Tomography, Emission-Computed
D002250:Carbon Radioisotopes; D002352:Carrier Proteins; D000697:Central Nervous System Stimulants; D050483:Dopamine Plasma Membrane Transport Proteins; D018765:Dopamine Uptake Inhibitors; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; C493214:SLC6A3 protein, human; D008774:Methylphenidate