Interactive processing between glutamatergic and cholinergic systems involved in inhibitory avoidance learning of rats

Rats were tested with a one-trial inhibitory avoidance paradigm in which the latency to enter the shock compartment served as a measure of memory retention. Pretraining administration of the non-competitive NMDA receptor antagonist MK-801 (0.3 mg/kg i.p.) significantly reduced the response latency during the retention test given 24 h after rats received a step-through inhibitory avoidance training. MK-801 at 0.1 mg/kg did not affect the retention latency. The muscarinic receptor antagonist scopolamine (1.0 mg/kg i.p.) also interfered with the inhibitory avoidance response in the retention test when administered before the training trial. The lower dose of 0.3 mg/kg scopolamine, which by itself was ineffective, significantly impaired inhibitory avoidance learning when administered simultaneously with the behaviorally subthreshold dose of 0.1 mg/kg MK-801 before the training trial. These results suggest that interactive mechanisms regulated by concurrent activation of NMDA and muscarinic receptors are involved in learning processes of inhibitory avoidance performance in rats.