The Interaction of Cholinergic Muscarinic and Beta-1 Adrenergic Receptors of the CA1 Region in Passive Avoidance Memory Formation in Rat

It is well known that involvement of muscarinic cholinergic and beta noradrenergic systems in process of the memory formation. But، up to now interaction of these systems in the CA1 region of hippocampus is not studied in memory formation. The aim of this study was to investigate the interaction of muscarinic and? 1-adrenergic receptors in the CA1 on memory retrieval. In this experimental research، 77 Wistar adult male rats (200-250 g) were used. Animals (in 11 groups) cannulated for CA1 region with stereotaxic surgery and trained in step-through apparatus: saline group (1µl/rat)، pilocarpine groups (0. 5، 1، 2 µg/rat)، betaxolol groups (0. 25، 0. 5، 1 µg/rat)، other four groups included saline/saline، pilocarpine2/saline، pilocarpine2/ betaxolol 0. 25، pilocarpine2/ betaxolol 0. 5. Drugs injected as intra-CA1 after training and memory tested after 24 hours. The latencies to enter and times spent in dark compartment of apparatus were recording for the evaluation of memory retrieval. Injection of 2 µg/rat of pilocarpine، a muscarinic receptor agonist، increased the latencies to enter dark compartment (291. 4±5. 6sec) and decreased the times spent in this compartment (8. 6±5. 5sec، p<0. 05). This effect was reversed by the ineffective low doses of betaxolol (0. 25 and 0. 5)، a? 1-adrenergic receptor antagonist، (p<0. 01 and p<0. 001 respectively). The latencies to enter dark compartment was 122±47. 3 and 62±10. 6 sec. Also، the times spent in this compartment was134. 6±35. 4 and 192±23. 2sec respectively. It is suggested that enhancement of the inhibitory avoidance memory retrieval، induced by activation of muscarinic cholinergic system of the dorsal hippocampal CA1 region، may be mediated via? 1-adrenergic receptors related mechanisms.