Learning versus performance impairments following regional administration of MK-801 into nucleus accumbens and dorsomedial striatum

To further ascertain the relative contributions of nucleus accumbens (NAC) and dorsomedial striatum (DS) to cognitive behaviors, the comparative effec ts in rats of MK-801 microinjections into these regions on a multiple sched ule of repeated learning (RL) and performance (P) were examined. The RL com ponent required learning of a new three-member response sequence during eac h experimental session, while the P component required rote performance of a pre-learned response, thus permitting a more precise delineation of treat ment-related cognitive vs, non-cognitive changes. MK-801 decreased overall accuracy in both the RL and P components of the schedule in both brain regi ons, indicating that in neither NAC nor DS are NMDA receptors exclusively i nvolved in mediating acquisition processes. Decreases in overall accuracy w ere primarily due to increased perseverative errors which may have been the result of excessively accelerated responding, a type of motoric alteration . MK-801 administered into NAC also resulted in an additional increase in s kipping errors at the 2.5 mu g dose, a finding which could be consistent wi th disrupted learning resulting from an inability to encode spatial relatio nships. Collectively these findings suggest that NAC and DS mediate some be havioral functions in common, but that additional cognitive-related spatial processes are mediated by NAG. (C) 1999 Elsevier Science B.V. All rights r eserved.