Interleukin (IL)-1 beta is one of the important proinflammatory cytokines in neural as well as immune systems, and plays a pivotal role in the neuroinflammation. We previously demonstrated that cerebellar IL-1 beta is involved in kainate-induced ataxia, i.e., IL-1 beta was activated in the cerebellum with systemic administration of kainate, and its type I receptor (IL-IR) was expressed at a soma of cerebellar Purkinje cells. In this study, we examined the effect of IL-1 beta on cerebellar Purkinje cell function by recording extracellular neuronal activities in anesthetized mice. Systemic administration of kainate increased the firing rates of cerebellar Purkinje cells in normal mice but showed little effect in IL-1R-knockout (IL-IR-KO) mice. Moreover, microiontophoretic administration of IL-1 beta to cerebellar Purkinje cells increased the firing rates promptly in response to IL-1 beta. The present results demonstrate that IL-1 system exerts a direct modulatory effect on cerebellar Purkinje cells. (C) 2008 Elsevier Inc. All rights reserved.