CHRONIC TREATMENT WITH MK-801 AFFECTS THE BEHAVIORAL-RESPONSE TO BOTHD-1 AND D-2 DOPAMINE AGONIST IN THE ONE-TRIAL INHIBITORY AVOIDANCE

Post-training administration of the N-methyl-D-aspartate (NMDA) antago nists CPP (0.5 and 1.0 mg/kg) and MK-801 (0.25 and 0.5 mg/kg) impaired , in a dose dependent fashion, the one-trial inhibitory avoidance resp onse in NMRI mice. The D-1 dopamine (DA) agonist SKF 38393 (10 and 20 mg/kg) and the D-2 agonist quinpirole (0.5 and 1.0 mg/kg) instead faci litate the response in the same behavioral paradigm. Sub-chronic block ade of NMDA receptors with MK-801 (0.25 mg/kg once a day for 14 days) did not change the response to both competitive (CPP) and non-competit ive (MK-801) NMDA antagonists. The same chronic treatment with MK-801 induced an increased response to both SKF 38393 and quinpirole. These data suggest that repeated administration of MK-801 induce an upregula tion of both D-1 and D-2 DA receptors without affecting NMDA receptors .