EFFECTS OF THE POTASSIUM CHANNEL BLOCKERS, APAMIN AND 4-AMINOPYRIDINE, ON SCOPOLAMINE-INDUCED DEFICITS IN THE DELAYED MATCHING TO POSITION TASK IN RATS - A COMPARISON WITH THE CHOLINESTERASE INHIBITOR E2020

The effects of the muscarinic antagonists, scopolamine HBr and MeBr, a cholinesterase inhibitor, E2020, and K+ channel blockers, 4-aminopyri dine (4-AP) and apamin. on the performance of rats in a delayed matchi ng to position (DMTP) task were examined. The percentage of correct ch oices (choice accuracy), number of trials completed and intertrial int ervals were measured. Discriminability and response bias were also cal culated, using signal detection analysis. Scopolamine HBr (0.1 mg/kg), but not scopolamine MeBr (0.1 mg/kg), significantly and consistently reduced the choice accuracy and discriminability, but neither affected the other measurements. E2020 (0.03-1.0 mg/kg) had no effect on the b aseline performance in the DMTP task, but at 1.0 mg/kg, it significant ly attenuated the deficits in choice accuracy induced by scopolamine. 4-AP (0.001-0.1 mg/kg) had no effect on either baseline performance or deficits induced by scopolamine. Apamin (0.1-0.3 mg/kg) had no effect on choice accuracy and discriminability. Apamin also failed to attenu ate the scopolamine-induced deficits. When administered in combination with scopolamine, apamin at 0.4 mg/kg significantly decreased the num ber of trials completed and increased the intertrial interval relative to that of the control group. Taken together, these results demonstra te that K+ channel blockers (4-AP and apamin), unlike a cholinesterase inhibitor (E2020). fail to reverse the scopolamine-induced deficits i n the DMTP task.