Epilepsy and inflammation in the brain: overview and pathophysiology

The possibility that inflammatory processes in the brain contribute to the etiopathogenesis of seizures and the establishment of a chronic epileptic focus is increasingly recognized as a result of supportive evidence in experimental models and in the clinical setting. Prototypical inflammatory cytokines (such as IL-1beta) and "danger signals" (such as HMGB1 and S100beta) are overexpressed in human and experimental epileptogenic tissue, prominently by glia. Neurons and endothelial cells of the blood-brain barrier contribute to inflammatory processes. All these cell types also express receptors for inflammatory mediators, suggesting that inflammatory molecules in the brain exert both autocrine and paracrine activation of intracellular signaling cascades; thus, they may act as soluble mediators of cell communication in diseased tissue. In experimental models, seizures also trigger brain inflammation in the absence of cell loss; in human epileptogenic tissue, the type of neuropathology associated with chronic seizures contributes to determine the type of cells expressing the inflammatory mediators, and the extent to which inflammation occurs. Inflammatory molecules, such as IL-1beta and HMGB1, have proconvulsant activity in various seizure models, most likely by decreasing seizure threshold via functional interactions with classical neurotransmitter systems. These findings reveal novel glioneuronal communications in epileptic tissue that highlight potential new targets for therapeutic intervention.