BEHAVIORAL-EFFECTS OF 7-OH-DPAT ARE SOLELY DUE TO STIMULATION OF DOPAMINE D-2 RECEPTORS IN THE SHELL OF THE NUCLEUS-ACCUMBENS - TURNING BEHAVIOR

The goal of this study was to determine whether the dopamine D-3 recep tor in limbic structures plays a role in the shell-specific and dopami ne-dependent display of turning behaviour in rats. When combined with the dopamine D-1 receptor agonist henyl-2,3,4,5-tetrahydro-1H-3-benzaz epine-7,8-diol (SKF-38393, 5 mu g), the putative dopamine D-3 receptor agonist (+/-)-7-hydroxy-N,N-di-n-propyl-2-aminotetralin (7-OH-DPAT, 1 , 5 and 10 mu g) elicited contralateral turning in a dose-dependent ma nner following unilateral injection into the shell, but not the core, of the nucleus accumbens. The turning pattern displayed was identical to that reported previously after intra-accumbens administration of th e cocktail of SKF-38393 and the dopamine D-2 receptor agonist quinpiro le. The behaviour under study was dose-dependently attenuated by local administration of the dopamine D-1 receptor antagonist ethyl-1-phenyl -2,3,4,5-tetrahydro-1H-3-benzazepine (SCH 23390: 10 and 100 ng), the d opamine D-2 receptor antagonist domperidone (25 and 50 ng) or the dopa mine D-2/3 receptor antagonist l-sulpiride (5 and 25 ng). Combined blo ckade of both dopamine D-1 and D-2 receptors in the shell with a dose of either antagonist alone that produced just a moderate reduction (10 ng SCH 23390 and 50 ng domperidone) completely antagonized the turnin g behaviour elicited by the cocktail of SKF-38393 and 7-OH-DPAT. Repla cing 7-OH-DPAT by another putative dopamine D-3 receptor agonist, prop yl-2H,5H-[1]benzopyrano[4,3-b]-1,4-oxazin-9-ol (PD 128,907, 10 mu g), in the cocktail did produce no turning behaviour at all. It is conclud ed that mesolimbic dopamine D-3 receptors play no role in the dopamine -dependent and shell-specific turning behaviour: the contribution of 7 -OH-DPAT in the cocktail of SKF-38393 and 7-OH-DPAT to the display of turning behaviour is solely due to its ability to activate dopamine D- 2 receptors.