Involvement of dopamine D2 receptors in complex maze learning and acetylcholine release in ventral hippocampus of rats

In the current study we focus on the involvement of dopamine D2 receptors in the ventral hippocampus in memory performance and acetylcholine release. Using the aversively motivated 14-unit T-maze (Stone maze) the injection of raclopride, a D2 receptor antagonist, into the ventral hippocampus (8 μg/kg) was found to impair memory performance. Co-injection of quinpirole, a D2 receptor agonist (8 μg/kg), overcame the impairment in performance. Microdialysis study revealed that quinpirole infusion (10–500 μM) into the ventral hippocampus stimulated acetylcholine release in a dose-dependent manner, and systemic injection of quinpirole (0.5 mg/kg, i.p.) also stimulated acetylcholine release in the ventral hippocampus. Infusion of eticlopride, another D2receptor antagonist, into the ventral hippocampus suppressed acetylcholine release in the hippocampus induced by systemic injection of quinpirole. Taken together, we suggest that D2 receptors in the ventral hippocampus are involved in memory performance, possibly through the regulation of acetylcholine.