Abstracts

Rationale: A common rodent model of temporal epilepsy encompasses the peripheral administration of lithium chloride, followed by scopolamine and pilocarpine. The activation of cholinergic neurons in the limbic system is believed to be a crucial factor responsible for the onset of seizures. We recently demonstrated that peripheral pro-inflammatory events and blood brain barrier (BBB) disruption may contribute to the onset of Status Epilepticus (SE) in the pilocarpine model of epilepsy [1]. We hypothesized that a similar peripheral mechanism may also occur and contribute to the SE in the lithium-pilocarpine model of epilepsy. Methods: We evaluated the integrity of the BBB 20 hrs after intraperitoneal injection of lithium chloride performed in adult rats. Damage in the cerebrovasculature was assessed by micro-angiography (FITC-Albumin) while reactive gliosis was evaluated by GFAP staining. Cresyl violet staining was performed to study the microanatomy of different brain structures. The effect of lithium on BBB permeability was also evaluated in vitro using a Transwell system obtained with a co-culture of human derived brain endothelial cells and human astrocytes in the presence or not of monocytes. Morphological changes of endothelial cells were evaluated by fluorescent immunocytochemistry using β-actin staining. Results: Lithium-induced damage of the BBB was observed in the temporal cortex, including the hippocampus. Leakage of the BBB was associated with regions of reactive gliosis, a pronounced swelling-induced midline shift and enlargement of the ventricles, suggestive of brain edema. In vitro, lithium treatment reduced the trans-endothelial resistance of the BBB in the presence of monocytes. Co-application of pilocarpine potentiated this effect. Immunocytochemical studies revealed changes in the cytoskeletal structure of endothelial cells when exposed to lithium, alone or in combination with pilocarpine. Endothelial degradation of β-actin and loss of tight junctions was also observed after exposure to either lithium alone or in combination with pilocarpine.Conclusions: Our results demonstrate that, in vivo and in vitro, lithium alone or together with pilocarpine can perturb the integrity of BBB. The changes in BBB permeability induced by lithium prior to treatment with pilocarpine may have a priming effect that contributes to the onset of seizures in the Lithium-Pilocarpine model. [1]Marchi,N. et al. In vivo and in vitro effects of pilocarpine: relevance to epileptogenesis. Epilepsia in press, (2007). (Supported by NIH-NS43284, NIH-HL51614, NIH-NS46513, NIH-NS049514 and NIH-NS38195)