Role of dopamine D2 receptors of the dorsal hippocampus on scopolamine state-dependent memory

Cholinergic and dopaminergic systems of the brain play an important role in learning and memory. In the present study, we assessed the role of dopamine D2 receptors of the dorsal hippocampus in scopolamine induced amnesia and scopolamine state-dependent memory in adult male rats. In this experimental study 200 adult male Wistar rats were used (25 group). Rats were anesthetized and then placed in a stereotaxic apparatus. Two stainless-steel cannula were placed 1 mm above CA1 region of dorsal hippocampus. One week later animals were trained in a step-through type inhibitory avoidance task. Pre-training intra-CA1 administration of scopolamine impaired memory retrieval on the test day. The memory impairment induced by pre-training injection of scopolamine was reversed by pre-test administration of scopolamine or quinpirole, which indicated scopolamine induced state-dependent learning and the effect of dopamine D2 receptors of the dorsal hippocampus on this type of learning. Furthermore, memory impairment was produced following pre-test intra-CA1 injection of dopamine D2 receptor antagonist, sulpiride. Pre-test intra-CA1 injection of sulpiride also inhibited scopolamine-induced state-dependent memory. These results suggested that dopaminergic D2 receptors of the dorsal hippocampal CA1 region may play an important role in scopolamine-induced amnesia and scopolamine state-dependent memory.