Morphine-conditioned single-trial place preference: role of nucleus accumbens shell dopamine receptors in acquisition, but not expression.
BACKGROUND
A large body of evidence indicates an involvement of the mesolimbic dopamine (DA) pathway innervating the ventral striatum in the motivational effects of drug abuse.


OBJECTIVE
The goal of the study is to clarify the role of DA D1 and D2 receptors of the rat nucleus accumbens (NAc) shell and core in the motivational effects of morphine as studied by conditioned place preference (CPP).


METHODS
The effect of the intracerebral infusion of DA antagonists specific for DA D1 (SCH 39166) and D2 receptors (L-sulpiride) was studied in a single-trial place conditioning paradigm with fixed assignment of the drug to the unpreferred compartment.


RESULTS
Morphine induced significant CPP at all the doses tested (0.5, 1.0, and 2.0 mg/kg, subcutaneously). A dose of 1.0 mg/kg was selected for further studies. Intra-NAc shell infusion of SCH 39166 and L-sulpiride at doses of 25 and 50 ng/1 microl per side impaired the acquisition of CPP by morphine. No effect was observed at 12.5 ng/1 microl per side. Intra-NAc core infusion of SCH 39166 (12.5, 25, and 50 ng/1 microl per side) did not affect the acquisition of morphine-induced CPP, while L-sulpiride (12.5, 25, and 50 ng/1 microl per side) impaired CPP acquisition only at the dose of 50 ng/1 microl per side. No effect on morphine-induced CPP was observed when the DA antagonists were infused into the NAc shell or core 10 min before the test session.


CONCLUSIONS
These results indicate that DA D1 and D2 receptors in the NAc shell are involved in the acquisition of morphine-induced CPP.
Fenu
Sandro
S
Department of Toxicology, University of Cagliari, Via Ospedale 72, Cagliari 09124, Italy.
Spina
Liliana
L
Rivas
Emilia
E
Longoni
Rosanna
R
Di Chiara
Gaetano
G
D000818:Animals; D001245:Association Learning / Q000187:drug effects*; D001552:Benzazepines / Q000494:pharmacology; D001931:Brain Mapping; D002755:Choice Behavior / Q000187:drug effects*; D003214:Conditioning, Classical / Q000187:drug effects*; D065127:Dopamine D2 Receptor Antagonists; D004305:Dose-Response Relationship, Drug; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D009294:Narcotics / Q000494:pharmacology*; D009714:Nucleus Accumbens / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017447:Receptors, Dopamine D1 / Q000037:antagonists & inhibitors / Q000187:drug effects*; D017448:Receptors, Dopamine D2 / Q000187:drug effects*; D012931:Social Environment; D013469:Sulpiride / Q000494:pharmacology
D001552:Benzazepines; D065127:Dopamine D2 Receptor Antagonists; D009294:Narcotics; D017447:Receptors, Dopamine D1; D017448:Receptors, Dopamine D2; C058081:ecopipam; D009020:Morphine; D013469:Sulpiride