The mechanisms involved in the pathogenesis of epilepsy, a chronic neurological disorder that affects approximately 1 percent of the world population, are not well understood [1][2][3] . Using a mouse model of epilepsy, we show that seizures induce elevated expression of vascular cell adhesion molecules and enhanced leukocyte rolling and arrest in brain vessels mediated by the leukocyte mucin P-selectin glycoprotein ligand-1 (PSGL-1) and leukocyte integrins α4β1 and αLβ2. Inhibition of leukocytevascular interactions either with blocking antibodies, or in mice genetically deficient in functional PSGL-1, dramatically reduced seizures. Treatment with blocking antibodies following acute seizures prevented the development of epilepsy. Neutrophil depletion also inhibited acute seizure induction and chronic spontaneous recurrent seizures. Blood-brain barrier (BBB) leakage, which is known to enhance neuronal excitability, was induced by acute seizure activity but was prevented by blockade of leukocyte-vascular adhesion, suggesting a pathogenetic link between leukocyte-vascular interactions, BBB damage and seizure generation. Consistent with potential leukocyte involvement in the human, leukocytes were more abundant in brains of epileptics than of controls. Our results Correspondence should be addressed to: P.F.F (E-mail: paolo.fabene@univr.it) or G.C. (E-mail: gabriela.constantin@univr.it). Author contribution G.N.M., D.B., A.C., L.Z., F.S. performed epilepsy experiments, telemetry and open field behavior. M.M., B.R., L.O., S.B., S.A., performed intravital microscopy, in vivo staining for adhesion molecules, adhesion assays and contributed to the obtainment of behavioral data. A.O. provided the human samples. F.M., A.C. and F.O. performed immunohistochemistry on human and animal samples. P.M., E.N. and A.S provided MRI expertise. J.W.H., L.X., J.B.L., R.P.M provided vital reagents and mice. E.C.B contributed experimental suggestions, reagents and assistance with writing. P.F.F and G.C. designed the study, analyzed the data and wrote the paper NIH Public Access suggest leukocyte-endothelial interaction as a potential target for the prevention and treatment of epilepsy.Experimental data from animal models as well as human evidence indicate that seizures can lead to neuronal damage and cognitive impairement 2, 3 . However, the molecular mechanisms leading to seizures and epilepsy are not well understood. Recent data suggests that inflammation may play a role in the pathogenesis of epilepsy 4, 5 . For instance, elevation in inflammatory cytokines are seen in the central nervous system (CNS) and plasma in experimental models of seizures and in clinical cases of epilepsy 4, 5 . Moreover, CNS inflammation is associated with breakdown in the blood-brain barrier (BBB), and BBB leakage has been implicated both in the induction of seizures and in the progression to epilepsy 6-9 . Leukocyte recruitment is a hallmark of and a point of therapeutic intervention in tissue inflammation 10,11 , but a role for leukocyte-endothelia...

In refractory temporal lobe epilepsy, seizures often arise from a shrunken hippocampus exhibiting a pattern of selective neuron loss called "classic hippocampal sclerosis." No single experimental injury has reproduced this specific pathology, suggesting that hippocampal atrophy might be a progressive "endstage" pathology resulting from years of spontaneous seizures. We posed the alternate hypothesis that classic hippocampal sclerosis results from a single excitatory event that has never been successfully modeled experimentally because convulsive status epilepticus, the insult most commonly used to produce epileptogenic brain injury, is too severe and necessarily terminated before the hippocampus receives the needed duration of excitation. We tested this hypothesis by producing prolonged hippocampal excitation in awake rats without causing convulsive status epilepticus. Two daily 30-minute episodes of perforant pathway stimulation in Sprague-Dawley rats increased granule cell paired-pulse inhibition, decreased epileptiform afterdischarge durations during 8 hours of subsequent stimulation, and prevented convulsive status epilepticus. Similarly, one 8-hour episode of reduced-intensity stimulation in Long-Evans rats, which are relatively resistant to developing status epilepticus, produced hippocampal discharges without causing status epilepticus. Both paradigms immediately produced the extensive neuronal injury that defines classic hippocampal sclerosis, without giving any clinical indication during the insult that an injury was being inflicted. Spontaneous hippocampal-onset seizures began 16-25 days post-injury, before hippocampal atrophy developed, as demonstrated by sequential magnetic resonance imaging. These results indicate that classic hippocampal sclerosis is uniquely produced by a single episode of clinically "cryptic" excitation. Epileptogenic insults may often involve prolonged excitation that goes undetected at the time of injury.

Under certain experimental conditions, neurotrophic factors may reduce epileptogenesis. We have previously reported that local, intrahippocampal supplementation of fibroblast growth factor-2 (FGF-2) and brain-derived neurotrophic factor (BDNF) increases neurogenesis, reduces neuronal loss, and reduces the occurrence of spontaneous seizures in a model of damage-associated epilepsy. Here, we asked if these possibly anti-epileptogenic effects might involve anti-inflammatory mechanisms. Thus, we used a Herpes-based vector to supplement FGF-2 and BDNF in rat hippocampus after pilocarpine-induced status epilepticus that established an epileptogenic lesion. This model causes intense neuroinflammation, especially in the phase that precedes the occurrence of spontaneous seizures. The supplementation of FGF-2 and BDNF attenuated various parameters of inflammation, including astrocytosis, microcytosis and IL-1β expression. The effect appeared to be most prominent on IL-1β, whose expression was almost completely prevented. Further studies will be needed to elucidate the molecular mechanism(s) for these effects, and for that on IL-1β in particular. Nonetheless, the concept that neurotrophic factors affect neuroinflammation in vivo may be highly relevant for the understanding of the epileptogenic process.