Differential impairments of rat serial pattern learning and retention induced by MK-801, an NMDA receptor antagonist

Three experiments investigated the role of NMDA receptor dependent systems in sequential learning and memory. Rats tracked serial patterns after syste mic administration of MK-801, an NMDA receptor antagonist that blocks plast icity in the hippocampus and other structures. Experiments 1 and 2 sought t o describe the effects of MK-801 on acquisition and retention of serial pat terns. Patterns were 2 1 elements long and highly organized, with some grou ps receiving a "violation" element that did not fit the organization of the rest of the pattern. Experiment 3 evaluated MK-801's effects on the integr ation of new information that was either consistent or inconsistent with a preciously learned pattern structure. The results of these experiments indi cated that MK-801 interfered with serial pattern learning and, to a lesser degree, retention. Learning about structure was relatively spared, whereas learning about interruptions or violations of pattern structure was impaire d. The latter differential effects are consistent with the contention in ea rlier literature that serial pattern learning is subserved by at least two learning/memory systems.