MK-801 potentiates morphine-induced impairment of memory consolidation in mice: involvement of dopaminergic mechanisms.

The purpose of the present research was to study the interaction between the non-competitive NMDA receptor antagonist MK-801 and morphine in memory consolidation. The involvement of dopamine (DA) mechanisms in this interaction was also studied. Four sets of experiments were carried out with CD1 mice in a one-trial inhibitory avoidance task with post-training injections of drugs. In a first series of experiments post-training administration of morphine or of the non-competitive NMDA receptor antagonist MK-801 impaired memory consolidation. In the second set of experiments the memory consolidation impairment exerted by MK-801 was potentiated by the administration of the D1 dopamine (DA) receptor antagonist SCH 23390 and by that of the D2 DA receptor antagonist (-)-sulpiride. In the third set of experiments, administration of a dose of MK-801 ineffective by itself potentiated the memory impairment exerted by morphine. In the fourth series of experiments, similar ineffective doses of the D1 DA receptor agonist SKF 38393 or of the D2 DA receptor agonist LY 171555 antagonized the impairment of memory consolidation produced by MK-801 and morphine in combination, suggesting the involvement of dopaminergic mechanisms.