Dopamine D2High receptors measured ex vivo are elevated in amphetamine-sensitized animals.
Although dopamine supersensitivity is a fundamental aspect of diseases such as schizophrenia and Parkinson's disease, the molecular basis of dopamine supersensitivity is not known. Because behavioral dopamine supersensitivity is associated with a marked elevation of striatal dopamine D2(High) receptors in vitro, it is important to develop methods to measure D2(High) receptors in vivo. The present ex vivo study found that the dopamine agonist NPA ([-]-N-propyl-norapomorphine) inhibited the binding of the agonist [(3)H](+)PHNO to rat striatal D2 receptors significantly more than the D2 antagonist [(3)H]raclopride, when NPA was coinjected i.v. with each radioligand. These results suggest that the greater sensitivity of [(3)H](+)PHNO to inhibition by the coinjected NPA reflects in vivo competition at D2(High) receptors. Using rats that had been sensitized to amphetamine, this ex vivo method found that the specific binding of [(3)H](+)PHNO that was displaced by 10 microg/kg of NPA was 2.4-fold higher than that for control rats. These data agree with in vitro data showing a marked increase in D2(High) sites after amphetamine sensitization. Therefore, it is recommended that this method of co-injecting the D2 radioligand and the dopamine agonist displacer be used in human positron tomography to detect D2(High) receptors in health and disease.
Seeman
Philip
P
Clera Inc., 260 Heath Street West, Toronto, Ontario, Canada. Phil@clera.com
D000661:Amphetamine / Q000494:pharmacology*; D000818:Animals; D001058:Apomorphine / Q000031:analogs & derivatives / Q000494:pharmacology; D001667:Binding, Competitive / Q000187:drug effects; D000697:Central Nervous System Stimulants / Q000494:pharmacology*; D003342:Corpus Striatum / Q000187:drug effects* / Q000378:metabolism*; D018491:Dopamine Agonists / Q000494:pharmacology; D018492:Dopamine Antagonists / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D011485:Protein Binding / Q000187:drug effects; D020891:Raclopride / Q000494:pharmacology; D051381:Rats; D017448:Receptors, Dopamine D2 / Q000819:agonists / Q000378:metabolism*; D014316:Tritium / Q000494:pharmacology
C425777:10,11-dihydroxy-N-n-propylnorapomorphine; D000697:Central Nervous System Stimulants; D018491:Dopamine Agonists; D018492:Dopamine Antagonists; D017448:Receptors, Dopamine D2; D014316:Tritium; D020891:Raclopride; D000661:Amphetamine; D001058:Apomorphine