EFFECTS OF THE NMDA-ANTAGONIST, MK-801, ON STRESS-INDUCED ALTERATIONSOF DOPAMINE DEPENDENT BEHAVIOR

The effects of pretreatment with the noncompetitive NMDA antagonist ()MK-801 on the behavioral alterations induced by repeated restraint st ress were investigated. Repeatedly stressed (restraint stress 2 h a da y x 10 days) mice showed enhanced sensitivity to the inhibitory effect s of a low dose of direct dopamine agonist, apomorphine (0.25 mg/kg), on climbing behavior. On the other hand, no changes were observed for the stimulatory effect of the high dose of apomorphine (3 mg/kg) on th is behavioral response. Mice pretreated with MK-801 (0.15 mg/kg) befor e the stressful experience did not show altered response to the low do se of apomorphine (0.25 mg/kg). Finally, ten daily injections with 0.1 5 mg/kg MK-801 did not affect the behavioral response to the low dose of apomorphine, but enhanced the stimulatory effect of the high dose o f the dopaminergic agonist on climbing behavior. Therefore, it is poss ible that the protective action of MK-801 against stress-induced behav ioral alteration is due to changes in sensitivity of postsynaptic rece ptors.