The Blockade of D-1/D-2-Like Dopamine Receptors within the Dentate Gyrus of Hippocampus Decreased the Reinstatement of Morphine-Extinguished Conditioned Place Preference in Rats

Introduction: The hippocampus (HIP), the primary brain structure related to learning and memory, receives sparse but comprehensive dopamine innervations and contains dopamine D-1/D-2-like receptors. It is demonstrated that dopamine receptors in dentate gyrus (DG) region of HIP have a remarkable function in spatial reward processing. Much less is known about the involvement of HIP and its D-1/D-2 dopamine receptors in drug-seeking behaviors, more particularly, in the morphine extinguished conditioned place preference (CPP). Methods: To find out the role of D-1/D-2-like receptors within the DG in morphine-seeking behaviors, forty adult male albino Wistar rats weighing 220-280g were unilaterally implanted by a cannula into the DG. The CPP paradigm was done; conditioning score and locomotors activity were recorded by Ethovision software. All drugs/vehicles were microinjected one day after extinction (just before the CPP test) into the DG as reinstatement day. Results: The results showed that intra-DG administration of different dose of SCH23390 (0.25, 1 and 4 mu g/0.5 mu l saline), as a selective D-1-like receptor antagonist and sulpiride (0.25, 1 and 4 mu g/0.5 mu l DMSO), as a selective D-2-like receptor antagonist dose-dependently attenuated the morphine-extinguished CPP reinstated by priming injection of morphine (1 mg/kg, sc). Discussion: It can be concluded that D-1/D-2-like receptors within this region have an important role in morphine-seeking behaviors in extinguished rats.