Ethanol (1.5-3.5 g/kg body weight) was administered intraperitoneally to mice and the phosphorylation of MAP (mitogen-activated protein) kinase in the cerebral cortex was determined using phospho-specific MAP kinase antibodies. Ethanol inhibited the phosphorylation of MAP kinase in a dose- and time-dependent manner. Developmental studies demonstrated that the levels of phospho-MAP kinase increased from fetal cortex (prenatal) to 16-day-old mice (postnatal) and remained constant up to 4 months of age. However, ethanol (3.5 g/kg) decreased the phospho-MAP kinase staining in all of the age groups studied. Subcellular fractionation studies demonstrated that ethanol inhibited the phosphorylation of MAP kinase in both the cytosol as well as nucleus, but did not alter the levels of MAP kinase. Likewise, MK-801 (0.4 mg/kg) or flurazepam (75 mg/kg) also decreased the phospho-MAP kinase content. These data indicate that ethanol may inhibit the phosphorylation of MAP kinase in vivo by either inhibiting NMDA receptors or activating GABA receptors.