We have evaluated the effect of the systemic administration of MK-801 (0.4 mg/kg) on the gene expression of D-amino acid oxidase (DAO) in several brain areas of the rat. The levels of DAO mRNA in all the brain areas significantly increased and peaked at 4 h after the administration. The present results suggest that there is a link between the expression of DAO mRNA and the N-methyl-D-aspartate (NMDA) receptor activity. (C) 2004 Elsevier B.V. All rights reserved.