Abstracts

Rationale: Experimental and clinical evidence suggest that brain inflammation is involved in the pathogenesis of seizures. Inflammatory reactions occur in brain during the epileptic process; in particular, the pro-inflammatory cytokine interleukin(IL)-1beta is rapidly synthesized in rodent brain during seizures, and it is increased in epileptogenic tissue of drug resistant epilepsy patients. IL-1beta contributes to neuronal injury and the development of epilepsy. This cytokine was shown to compromise blood-brain barrier (BBB) integrity, which in turn may contribute to glial cell dysfunction and hyperexcitability. The aim of this study was to investigate parenchymal brain inflammation and BBB damage, after pharmacological induction of epileptiform activity in the vitro isolated guinea pig brain preparation. This approach allows to exclude any systemic or blood cells contribution to the effects of seizures and their consequences. Methods: Ictal activity was evoked by three-min infusion in the basilar artery of the GABA-A receptor antagonist bicuculline methiodide (50 M in artificial CSF). Epileptiform activity was recorded by simultaneous electrophysiological recordings in CA1 area of both hemispheres. Brain inflammation was evaluated by immunohistochemical detection of IL-1beta; BBB integrity was assessed in adjacent sections by detection of parenchymal extravasation of FITC-albumin artificially infused into the isolated brain after seizure induction. Results: Epileptiform activity induced by bicuculine lasted for 2 h (total time in seizures was ~30 min). Immunohistochemical analysis at the end of seizures revealed a significant expression of IL-1beta in glial cells, exclusively in those areas involved in ictal activity (i.e. limbic cortices). Adjacent slices showed parenchymal extravasation of FITC-albumin in brain areas where inflammation occurs. Control brains maintained in vitro for comparable time without bicuculline infusion, showed no IL-1beta immunoreactivity and only minor FITC-albumin extravasation, as compared to brains with epileptic activity. Conclusions: Seizure activity induced in vitro evokes IL-1beta expression in glia and concomitant BBB damage. These findings suggest that inflammatory mediators produced by glial cells during seizures are responsible for BBB breakdown observed in in vivo models of epilepsy, in the absence of contributions from peripheral immune cells. This mechanism may contribute to hyperexcitability underlying seizures.