Effects of blockade of NMDA receptors and NO synthase on the expression of associative and non-associative sensitization to effects of cocaine.

After repeated administration of psychostimulant drugs, a sensitization rather than a tolerance to the behavioral effects can be observed. In our own previous studies, it was shown that both blockade of NMDA glutamate receptors and inhibition of NO synthase selectively inhibited the expression of associative but not non-associative sensitization to D-amphetamine. The present experiments were performed in order to study whether a similar selective inhibition of expression of associative sensitization to cocaine can be observed after blockade of NMDA receptors by MK-801 or inhibition of NO synthase by L-NAME. MK-801 as well as L-NAME inhibited the locomotor activity in acutely cocaine-treated rats. Both drugs did not prevent the sensitization either in the associative or the non-associative group. The results suggest that the acute locomotor effects of cocaine were inhibited by both drugs whereas both the non-associative and the associative sensitization to locomotor effects were not inhibited by blockade of NMDA receptors or inhibition of NO synthase. Accordingly, the expression of neither type of sensitization to cocaine was inhibited by any of these drugs. Copyright (c) 2006 S. Karger AG, Basel.