Conditioned increase in place preference by access to novel objects: antagonism by MK-801

In three separate place conditioning experiments with rats, repeated access to novel objects in one of two distinct environments conditioned an increa se in preference for the novelty-paired environment. A conditioned increase in preference was found whether novel objects were paired with a randomly chosen environment or with the less preferred of two environments (conditio ned against a preference). This enhanced preference did not depend on the c ontrol group employed. Control groups exposed only to the place conditionin g apparatus or to both the apparatus and the novel objects showed no system atic shift in place preference. Intravenous infusions of cocaine also produ ced an increase in preference using the procedures employed with novel obje cts. Pretreatment with the N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 (0.03 mg kg(-1)) blocked acquisition of the enhanced place preferenc e conditioned by access to novel objects without decreasing time spent with objects or inducing a place aversion in controls. Combined, these results show that access to novel objects can serve as an appetitive stimulus like drugs of abuse and that this novelty-induced appetitive process involves NM DA receptors. These place-conditioning procedures may provide a good model for determining the behavioral and neural process underlying the appetitive effects of novelty. (C) 1999 Elsevier Science B.V. All rights reserved.