Dizocilpine prevents the development of tolerance to ethanol-induced error on a circular maze test

Dizocilpine [(+)MK-801] and ketamine, in doses that disrupt learning and memory, also prevent the development of tolerance to the motor impairing effects of ethanol (EtOH). However, dizocilpine itself affects motor behavior. In order to separate the possible influence of these two effects on the development of tolerance to EtOH, food-reinforced performance on a circular maze test was used in two different experiments. EtOH alone (1.2 g/kg) tended to increase the error score and reduce number of runs per trial, running speed, and total distance run, but on chronic administration of EtOH, tolerance developed progressively to all these effects. Dizocilpine also increased the error score, but had a biphasic effect on measures of running: low and intermediate doses (0.009 and 0.075 mg/kg, IP) increased running distance, whereas a high dose (0.15 mg/kg) decreased running speed and distance. When combined with EtOH, dizocilpine tended to overcome the effect of EtOH on running activity, but not on error score. Chronically, dizocilpine (0.075 and 0.15 mg/kg) prevented the development of tolerance to the effect of EtOH on error score, even though the lower dose of dizocilpine permitted tolerance to the effects of EtOH on running. These results suggest that NMDA receptor antagonists selectively inhibit tolerance to cognitive effects of ethanol even when the antagonists do not affect motor performance.