The cytokines interleukin-1 beta (IL-1 beta) and IL-1 receptor antagonist (IL-1ra) are rapidly induced in response to excitotoxic and ischemic brain damage. The aim of the present study was to investigate the influence of a non-competitive (dizocilpine maleate, MK-801) and a competitive ((R)-CPP) NMDA receptor antagonist on the transient cytokine expression in the rat brain induced by systemic kainic acid administration. Peripheral administration of kainic acid (10 mg/kg, i.p.) results in a transient expression of IL-1 beta and IL-1ra mRNA, mainly in microglia, in regions showing neurodegeneration such as the hippocampus, thalamus, amygdala, and certain cortical regions. In addition, a few neurons expressing IL-1ra mRNA were observed in the piriform cortex and amygdala following kainic acid injection. Administration of MK-801 (i.p.) 1 h prior to kainic acid injection reduced cytokine expression in all of these regions. MK-801 at 3.0 mg/kg decreased the IL-1 beta mRNA expression, blocked or decreased the IL-1ra mRNA expression, depending on the brain region. MK-801 at 5.0 mg/kg abolished IL-1ra mRNA expression in all of the regions, whereas the IL-1 beta mRNA expression was decreased or blocked, depending on the brain region, or the time point investigated. Peripheral administration of (R)-CPP (15 mg/kg, i.p.) 15 min prior to the kainic acid injection abolished the IL-1 beta mRNA expression. The IL-1ra mRNA expression was abolished in all regions except for a few neurons in the piriform cortex. The finding that NMDA receptor antagonists inhibit the IL-1 beta and IL-1ra mRNA synthesis induced by kainic acid suggests that NMDA receptor activation may be involved in triggering cytokine synthesis following excitotoxic brain damage.