In this study, we investigated the behavioral effects of MK-801 (1-20 micrograms) injected into the posterior parts of nucleus accumbens (ACC) and caudate-putamen (CP) in rats. Interactions of diazepam (DZP, 10 micrograms), haloperidol (HPD, 2 micrograms), and scopolamine (SCOP, 10 micrograms) with 20 micrograms of MK-801 were also studied. All injections were done in 2 microliters. In ACC, MK-801 increased locomotion, rearing, and head shakes. The effect of MK-801 especially at 20 micrograms was accompanied by a motor syndrome: head weaves, circling, body rolls, and ataxia. DZP nonsignificantly reduced the locomotion but it significantly (p < 0.05) reduced head shakes, weaves, circling, and body rolls produced by MK-801. HPD reduced grooming and head shakes. SCOP potentiated MK-801 hyperlocomotion, whereas it decreased body rolls, head shakes, and weaves. In CP, MK-801 increased locomotion, but less than in ACC (p < 0.05). The effect of MK-801 was significantly increased by SCOP. MK-801 also increased grooming (reduced by HPD and increased by SCOP) and at 5-20 micrograms induced oral movements that were decreased by HPD. These results indicate that the posterior part of ACC is involved in MK-801 hyperlocomotion and motor syndromes, whereas CP is involved in mediating grooming and oral movements. Blockade of the muscarinic cholinergic receptors seems to facilitate hyperlocomotion and decrease head shakes produced by MK-801. Mechanisms influenced by DZP and HPD appear to be involved in motor syndrome and oral movement, respectively, induced by MK-801, but not in hyperlocomotion.