β1-noradrenergic system of the dorsal hippocampus is involved in scopolamine state-dependent memory in rat

In the present study, we evaluated the possible effects of intra-CA1 administrations of β1-receptor agonist and antagonist, isoprenaline (isoproterenol) and atenolol respectively, on scopolamine state-dependent memory. Male Wistar rats were bilaterally implanted with chronic cannulae in the CA1 regions of the dorsal hippocampus, trained in a step-through type inhibitory avoidance task, and tested 24 h after training to measure step-through latency. Pre-training intra-CA1 injection of scopolamine (1.5 and 3 µg/rat) induced amnesia. The response induced by pre-training scopolamine was significantly reversed by pre-test administration of the drug that is due to a state-dependent effect. Although pre-test intra-CA1 administrations of isoprenaline alone had no effect, its administration (0.09 µg/rat) restored scopolamine amnesia. Furthermore, pre-test intra-CA1 injection of isoprenaline (0.01, 0.03 and 0.09 µg/rat) with an ineffective dose of scopolamine (0.25 µg/rat), synergistically improved memory performance impaired by pre-training scopolamine. The results also showed that pre-test intra-CA1 administrations of atenolol at dose of 0.09 µg/rat induced amnesia and disrupted state-dependent memory induced by scopolamine. Noteworthy, the response induced by the pre-test injection of isoprenaline plus scopolamine was antagonized with atenolol. These results suggest that β1-adrenergic receptors of the dorsal hippocampal CA1 regions may play an important role in scopolamine-induced amnesia and scopolamine statedependent memory.