Cooperative activation of D1-like and D2-like dopamine receptors in the nucleus accumbens shell is required for the reinstatement of cocaine-seeking bahavior in the rat

Activation of D1-like (D1, D5) or D2-like (D1, D3, D4) dopamine receptors in the nucleus accumbens shell is sufficient to reinstate cocaine-seeking behavior in rats. The goal of these experiments was to assess whether cooperative activation of D1-like and D2-like dopamine receptors in the accumbens shell is required to promote cocaine reinstatement. Rats were initially trained to self-administer cocaine (0.25 mg, Lv.) using a fixed-ratio schedule of reinforcement for approximately 21 days. Animals subsequently underwent an extinction phase during which saline was substituted for cocaine. Once cocaine self-administration behavior was extinguished (defined as < 15% of the total responses maintained during self-administration), dopamine receptor agonist-induced reinstatement of cocaine seeking was assessed. Administration of the selective D1/5 agonist R-(+)-6-chloro7,8-dihydroxy-l-phenyl-2,3,4,5-tetrahydro-1 H-3-benzazepine hydrobromide (SKF-81297) (1.0 mu g) or the D2/3 receptor agonist trans-(-)-(4aR)-4,4a,5,6,7,8,8a,9-octahydro-5propyl-IH-pyrazolo[3,4-g]quinoline hydrochloride (quinpirole) (3.0 mu g) directly into the nucleus accumbens shell promoted reinstatement of cocaine seeking. In order to determine if endogenous dopamine tone in the accumbens shell is required for dopamine receptor agonist-induced reinstatement of cocaine seeking, D1/5 or D2/3 dopamine receptor antagonists were administered into the nucleus accumbens shell prior to a selective cloparnine receptor agonist. Microinfusion of the D2/3 dopamine receptor antagonist sulpiride ((S)-5-aminosulfonyl-N[(1-ethyl-2-pyrrolidinyl)methyl]-2-methoxybenzamide) (1.0 mu g) into the nucleus accumbens shell 10 minutes prior to SKF81297 (1.0 mu g) blocked the ability of this D1-like clopamine receptor agonist to reinstate cocaine seeking. Similarly, administration of the selective D1/5 dopamine receptor antagonist R(+)-7-chloro-8-hydroxy-3-methyl-i-phenyl-2,3,4,5-tetrahy-dro-1H-3-benzazepine hydrochloride (SCH-23390) (1.0 mu g) into the nucleus accumbens shell prior to quinpirole (3.0 mu g) blocked reinstatement of drug-seeking behavior elicited by this D2/3 dopamine receptor agonist. Moreover, intra-accumbal shell co-administration of subthreshold doses of quinpirole (1.5 mu g) and SKF-81297 (0.1 mu g) promoted cocaine-seeking behavior. Collectively, these results indicate that cooperative activation of D1-like and D2-like dopamine receptors in the nucleus accumbens shell is necessary to reinstate cocaine seeking in rats. (c) 2006 IBRO. Published by Elsevier Ltd. All rights reserved.