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

Interleukin-1b (IL-1b) is overproduced in human and rodent epileptogenic tissue and it exacerbates seizures upon brain application in rodents.Moreover, pharmacological prevention of IL-1b endogenous synthesis, or IL-1 receptor blockade, mediates powerful anticonvulsive actions indicating a significant role of this cytokine in ictogenesis. The molecular mechanisms of the proconvulsive actions of IL-1b 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-1band 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-1b action suggesting that ceramide may be the second messenger of the proconvulsive effect of IL-1b. The seizure exacerbating effects of either IL-1b 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-1b effect was associated with increased Tyr phosphorylation of Src-family of kinases indicative of its activation, and Tyr 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-1b was blocked by ifenprodil, a selective NR2B receptor antagonist. These results indicate that the proconvulsive actions of IL-1b depend on the activation of a sphingomyelinaseand Src-family of kinasesdependent 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.