ROLE OF DOPAMINE D-1 AND D-2 RECEPTORS IN THE NUCLEUS-ACCUMBENS IN MEDIATING REWARD

The objectives of this study were to examine the involvement of D-1 an d D-2 receptors within the nucleus accumbens (ACB) in mediating reinfo rcement. The intracranial self-administration (ICSA) of D-1 and D-2 ag onists was used to determine whether activating D-1 and/or D-2 recepto rs within the ACB of Wistar rats is reinforcing. At concentrations of 0.25, 0.50, and 1.0 mM (25, 50, and 100 pmol/100 nl of infusion), neit her the D-1 agonist henyl-2,3,4,5-tetrahydro-1H-3-benzazepine-7,8-diol [SKF 38393 (SKF)] hydrochloride nor the D-2 agonist (-)-quinpirole (Q uin) hydrochloride was self-administered into the shell region of the ACE. On the other hand, equimolar mixtures of SKF and Quin (SKF+Quin), at concentrations of 0.25, 0.50, and 1.0 mM each, were significantly self-infused into the ACB shell. The core region of the ACB did not su pport the ICSA of SKF+Quin at any of these concentrations. Rats increa sed lever pressing when the response requirement was increased from a fixed ratio 1 (FR1) to FR3, and they responded significantly more on t he infusion lever than they did on the control lever. Coadministration of either 0.50 mM ethyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine (SCH 23390) hydrochloride, a D-1 antagonist, or 0.50 mM S(-)-sulpiride , a D-2 antagonist, completely abolished the ICSA of the mixture of SK F+Quin (each at 0.50 mM) into the ACB shell. The present results sugge st that concurrent activation of D-1- and D-2-type receptors in the sh ell of the ACB had a cooperative effect on DA-mediated reward processe s.