Background & Objectives: Several studies have shown that Glucocorticoids affect learning and memory processes by influences on limbic structures such as amygdala. The amygdala is an important region for memory formation. Considering the existence of the muscarinic acetylcholine receptors in the basolateral amygdala (BLA), the aim of the present study was to investigate the effect of intra-BLA microinjection of pilocarpine on the effect of dexamethasone on memory retrieval .

  Methods: As a model of learning, using a step-through apparatus , inhibitory avoidance was used for assessment of long-term memory in 80 adult male Wistar rats . All animals were bilaterally implanted with cannulas into the BLA and were trained and tested (with 24 h interval) 7 days after surgery. Memory retrieval was evaluated by recording of the step-through latencies and the time spent in dark chamber of apparatus in the testing day.

  Results: Pre-test subcutaneous (s.c) administration of dexamethasone (2 mg/kg) impaired memory retrieval in animals when trained 24 h in advance. Co-pretest microinjection of different doses of pilocarpine (1 , 2 μg/rat, intra-BLA ), a muscarinic acetylcholine receptor agonist, with the dexamethasone (2 mg/kg, s.c) caused enhancement of memory retrieval.

  Conclusion: Results of this research indicate that impairment effect of dexamethasone on memory processes may be mediates by decrease of mechanisms of BLA muscarinic cholinergic.