N-methyl-D-aspartate receptor antagonist MK-801 impairs learning but not memory fixation or expression of classical fear conditioning in goldfish (Carassius auratus).

Examined in 5 experiments the amnestic effects of the noncompetitive antagonist MK-801 on visually mediated, classic fear conditioning in goldfish (Carassius auratus). MK-801 was administered 30 min before the training session on Day 1 to look for anterograde amnestic effects, immediately after training to look for retrograde amnestic effects, and before the training or test session, or both, to look for state-dependence effects. Results show that MK-801 produced anterograde amnesia at doses that did not produce retrograde amnesia or state dependency and did not impair the expression of conditioned or unconditioned branchial suppression responses (BSRs) to the conditioned stimulus (CS). Results indicate that MK-801 disrupts the mechanism of learning of the CS–unconditioned stimulus (UCS) relation. Evidence is also presented that the learning processes that are disrupted by MK-801 occur during the initial stage of BSR conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)