Involvement of dorsal hippocampal beta-1 noradrenergic receptors in memory retrieval of rats

Central beta-noradrenergic system plays an important role in the learning and memory processes. Dorsal hippocampus also has an overlapped distribution of beta-noradrenergic receptors. The aim of this study was to evaluate the possible role of the dorsal hippocampal beta-1 noradrenergic receptors in memory retrieval using a passive avoidance learning task. This experimental study was performed on adult male Wistar rats (weight، 230±20gr). After anaesthetizing، the rats were cannulated into dorsal hippocampus using the stereotaxic surgery. After one week، passive avoidance memory was studied in two phases: training and testing with a 24h interval. The step-through latency to enter dark compartment and the time spent in this compartment was recorded for the evaluation of memory. All animals received drugs or saline، as intra- dorsal hippocampal microinjection، 30 min before testing. Pre-testing administration of dobutamine (1 μg/rat)، a beta-1 noradrenergic receptor agonist، potentiated passive avoidance memory retrieval، while pre-testing injection of betaxolol (0. 5μg/rat)، a beta-1 noradrenergic receptor antagonist، inhibited passive avoidance memory retrieval. Also، the injection of ineffective and low doses of betaxolol (0. 125 and 0. 25 μg/rat) inhibited the effect of dobutamine on the memory retrieval. It seems that beta-1 noradrenergic receptors of the dorsal hippocampus may mediate memory retrieval in a passive avoidance learning model.