Effects of the competitive N-methyl-D-aspartate receptor antagonist, CPP, on the development and expression of conditioned hyperactivity and sensitization induced by cocaine

This study used novel behavioral measures to examine the effects of the com petitive N-methyl-D-aspartate (NMDA) receptor antagonist, CPP, on the devel opment and expression of conditioned hyperactivity and sensitization produc ed with cocaine. The first experiment confirmed that horizontal locomotor a ctivity measured in the central zone of an activity enclosure could be incr eased by 10.0 mg/kg cocaine. This increased activity showed sensitization a fter repeated cocaine injections, and it could be conditioned to the test e nvironment. Subsequent experiments demonstrated that CPP (0.2 and 0.4 nmol, icv) could block the development, but not the expression, of conditioned h yperactivity and sensitization in the central zone. These findings confirm that NMDA receptors are critically involved in the development of condition ed hyperactivity and sensitization, but indicate that such receptors may no t be necessary for the expression of these neurobehavioral adaptations. (C) 1999 Elsevier Science B.V. All rights reserved.