Repeated treatment with the selective kappa opioid agonist U-69593 produces a marked depletion of dopamine D2 receptors.
U-69593, the selective K-opioid agonist, was repeatedly administered in single daily injections (0.32 mg/kg) to male, Sprague-Dawley rats. Two or ten days later, the rats were euthanized and dopamine D1 and D2 receptors were measured using (3H]SCH 23390 or [3H]sulpiride, respectively, in caudate putamen and nucleus accumbens. Two days after the last of three injections, dopamine D2 receptors in the caudate putamen were decreased by approximately 40%, with no change in D1 receptors. Dopamine D2 receptor number had returned to normal by 10 days posttreatment. In contrast, in the nucleus accumbens there was a small, nonsignificant decrease in dopamine D2 receptors 2 days after treatment, but a large increase (65%) after 10 days. In agreement with the changes in D2 receptors, there was a significant downward shift in the locomotor activity curve for the D2 agonist quinpirole after a 2-day withdrawal. There were no differences in either the total amount of dopamine taken up or in the IC50 for cocaine to inhibit dopamine uptake following this treatment, suggesting that the dopamine transporter and presynaptic terminals were intact. The results of these studies demonstrate that repeated administration of a selective K-opioid agonist induces long-term alterations in dopamine D2 receptors. Furthermore, the finding that these changes in receptor number require both repeated injections and a withdrawal time greater than 1 day suggests that these alterations are compensatory in nature.
Psychobiology Section, National Institute on Drug Abuse, Division of Intramural Research, National Institutes of Health, Baltimore, Maryland, USA. sizenwas@newssun.med.miami.edu
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Izenwasser
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Kunko
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Shippenberg
D000818:Animals; D001552:Benzazepines / Q000493:pharmacokinetics; D044482:Benzeneacetamides; D002352:Carrier Proteins / Q000378:metabolism; D002421:Caudate Nucleus / Q000187:drug effects / Q000502:physiology*; D050483:Dopamine Plasma Membrane Transport Proteins; D015536:Down-Regulation; D004334:Drug Administration Schedule; D008297:Male; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009043:Motor Activity / Q000187:drug effects; D009419:Nerve Tissue Proteins; D009714:Nucleus Accumbens / Q000187:drug effects / Q000502:physiology*; D011699:Putamen / Q000187:drug effects / Q000502:physiology*; D011759:Pyrrolidines / Q000494:pharmacology*; D019257:Quinpirole / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D017448:Receptors, Dopamine D2 / Q000378:metabolism*; D050637:Receptors, Dopamine D3; D017473:Receptors, Opioid, kappa / Q000037:antagonists & inhibitors*; D013469:Sulpiride / Q000493:pharmacokinetics; D013569:Synapses / Q000187:drug effects / Q000502:physiology*; D013997:Time Factors
D001552:Benzazepines; D044482:Benzeneacetamides; D002352:Carrier Proteins; D050483:Dopamine Plasma Membrane Transport Proteins; C493595:Drd3 protein, rat; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D011759:Pyrrolidines; D017448:Receptors, Dopamine D2; D050637:Receptors, Dopamine D3; D017473:Receptors, Opioid, kappa; D019257:Quinpirole; D013469:Sulpiride; C045444:U 69593