A novel non-transcriptional pathway mediates the proconvulsive effects of interleukin-1β

Interleukin-I beta (IL-I beta) is overproduced in human and rodent epileptogenic tissue and it exacerbates seizures upon brain application in rodents. Moreover, pharmacological prevention of IL-I beta endogenous synthesis, or IL-I receptor blockade, mediates powerful anticonvulsive actions indicating a significant role of this cytokine in ictogenesis. The molecular mechanisms of the proconvulsive actions of IL-I beta are not known. We show here that EEG seizures induced by intrahippocampal injection of kainic acid in C57BL6 adult mice were increased by 2-fold on average by pre-exposure to IL-I beta and this effect was blocked by 3-O-methylsphingomyelin (3-O-MS), a selective inhibitor of the ceramide-producing enzyme sphingomyelinase. C2-ceramide, a cell permeable analog of ceramide, mimicked IL-I beta action suggesting that ceramide may be the second messenger of the proconvulsive effect of IL-I beta. The seizure exacerbating effects of either IL-I beta or C2-ceramide were dependent on activation of the Src family of tyrosine kinases since they were prevented by CGP76030, an inhibitor of this enzyme family. The proconvulsive IL-I beta effect was associated with increased Tyr(418) phosphorylation of Src-family of kinases indicative of its activation, and Tyr(1472) phosphorylation of one of its substrate, the NR2B subunit of the N-methyl-D-aspartate receptor, which were prevented by 3-O-MS and CGP76030. Finally, the proconvulsive effect of IL-I beta was blocked by ifenprodil, a selective NR2B receptor antagonist. These results indicate that the proconvulsive actions of IL-I beta depend on the activation of a sphingomyelinase- and Src-family of kinases-dependent pathway in the hippocampus which leads to the phosphorylation of the NR2B subunit, thus highlighting a novel, non-transcriptional mechanism underlying seizure exacerbation in inflammatory conditions.