title: The modulatory actions of dopamine D2/3 agonists and antagonists on the locomotor-activating effects of morphine and caffeine in mice.
abstract: Morphine produces robust increases in locomotor activity in mice. Recent data indicate that dopamine (DA) D2/3 agonists attenuate the discriminative stimulus and antinociceptive effects of mu opioid agonists such as morphine. The present study was designed to determine the extent to which D2/3 receptor activation and blockade can modulate morphine-induced locomotion using a novel cumulative dosing procedure in Swiss-Webster mice. The results indicate that morphine-induced locomotion is nonsignificantly attenuated by the D2/3 agonists quinelorane and quinpirole, whereas the D2/3 antagonists eticlopride and nafadotride, as well as the partial D2/3 agonist BP897, significantly reduced morphine-induced locomotion. To determine the specificity of this modulation, these agonists and antagonists were examined in combination with caffeine, a drug that also indirectly alters DAergic activity. Unlike the effects on morphine, caffeine-induced locomotion was unaltered by eticlopride, nafadotride and BP897, but was attenuated by quinelorane and quinpirole. These results indicate that modulation of D2/3 receptors can, in turn, alter the locomotor-activating effects of morphine.
authors.affiliation: Department of Pharmacology and Toxicology, Virginia Commonwealth University, 410 North 12th Street, Smith Building, P.O. Box 980613, Richmond, VA 23298-0613, USA. ccook@hsc.vcu.edu
authors.forename: Charles D
authors.initials: CD
authors.lastname: Cook
authors.forename: Patrick M
authors.initials: PM
authors.lastname: Beardsley
mesh_terms: D000818:Animals; D002110:Caffeine / Q000037:antagonists & inhibitors* / Q000494:pharmacology*; D000697:Central Nervous System Stimulants / Q000037:antagonists & inhibitors* / Q000494:pharmacology*; D018491:Dopamine Agonists / Q000494:pharmacology*; D018492:Dopamine Antagonists / Q000494:pharmacology*; D065127:Dopamine D2 Receptor Antagonists; D004305:Dose-Response Relationship, Drug; D008297:Male; D051379:Mice; D009020:Morphine / Q000037:antagonists & inhibitors* / Q000494:pharmacology*; D009043:Motor Activity / Q000187:drug effects*; D009281:Naphthalenes / Q000494:pharmacology; D009292:Narcotic Antagonists; D009294:Narcotics / Q000494:pharmacology*; D011759:Pyrrolidines / Q000494:pharmacology; D011804:Quinolines / Q000494:pharmacology; D019257:Quinpirole / Q000494:pharmacology; D017448:Receptors, Dopamine D2 / Q000819:agonists*; D050637:Receptors, Dopamine D3; D012457:Salicylamides / Q000494:pharmacology; D014867:Water
chemical_list: D000697:Central Nervous System Stimulants; D018491:Dopamine Agonists; D018492:Dopamine Antagonists; D065127:Dopamine D2 Receptor Antagonists; C493594:Drd3 protein, mouse; D009281:Naphthalenes; D009292:Narcotic Antagonists; D009294:Narcotics; D011759:Pyrrolidines; D011804:Quinolines; D017448:Receptors, Dopamine D2; D050637:Receptors, Dopamine D3; D012457:Salicylamides; D014867:Water; D019257:Quinpirole; D002110:Caffeine; D009020:Morphine; C045989:eticlopride; C097285:nafadotride; C047726:quinelorane