Behavioural effects of 7-OH-DPAT are solely due to stimulation of dopamine D2 receptors in the shell of the nucleus accumbens; turning behaviour.

The goal of this study was to determine whether the dopamine D3 receptor in limbic structures plays a role in the shell-specific and dopamine-dependent display of turning behaviour in rats. When combined with the dopamine D1 receptor agonist (+/-)-1-phenyl-2,3,4,5-tetrahydro-1 H-3-benzazepine-7,8-diol (SKF-38393, 5 micrograms), the putative dopamine D3 receptor agonist (+/-)-7-hydroxy-N,N-di-n-propyl-2-aminotetralin (7-OH-DPAT, 1, 5 and 10 micrograms) elicited contralateral turning in a dose-dependent manner 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 the cocktail of SKF-38393 and the dopamine D2 receptor agonist quinpirole. The behaviour under study was dose-dependently attenuated by local administration of the dopamine D1 receptor antagonist R(+)-7-chloro-8-hydroxy-3- methyl-I-phroyl-2,3,4,5-tetrahydro-1H-3-benzazepine (SCH 23390: 10 and 100 ng), the dopamine D2 receptor antagonist domperidone (25 and 50 ng) or the dopamine D2/3 receptor antagonist l-sulpiride (5 and 25 ng). Combined blockade of both dopamine D1 and D2 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 turning behaviour elicited by the cocktail of SKF-38393 and 7-OH-DPAT. Replacing 7-OH-DPAT by another putative dopamine D3 receptor agonist,S(+)-(4aR, 10bR)-3,4,4a,10b-tetrahydro-4-propyl-2H,5H-[1]benzopyrano[4, 3-b]-1, 4-oxazin-9-ol (PD 128,907, 10 micrograms), in the cocktail did produce no turning behaviour at all. It is concluded that mesolimbic dopamine D3 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 D2 receptors.