Abstracts

Rationale: Epileptogenesis precipitated by status epilepticus (SE) is believed to evolve during a latent period which intervenes between SE and the emergence of spontaneous seizures. We have previously reported the evolution of pathological angiogenesis within specific limbic structures during this period, and the subsequent leakage of plasma born materials across the abnormal blood-brain barrier (BBB). Such BBB leakage has recently been shown to contribute directly to epileptogenesis. Here we report that SE-induced vascular pathogenesis is initiated by the expression of hypoxia inducible factor (HIF-1α) and vascular endothelial growth factor (VEGF), and that these cytokines/growth factors participate in the spatiotemporal evolution of these pathologies following SE. Methods: SE was induced in male wistar rats (250g – 350 g) by systemic kainic acid injection (10 mg/kg, i.v.), and terminated four hours after onset by injection of pentobarbital (20 mg/kg, i.p.) (KASE). The control group received vehicle injections and did not develop SE. Rats in separate cohorts were sacrificed 1, 3, 7, 14, 21, 35, 42, 49, 56, 63 days post-KASE. Bromodeoxyuridine (BrdU) injections (50 mg/kg, i.p.) were administered daily for seven consecutive days to separate cohorts beginning 1, 7, 14, 21, 28, 35, 42, or 49 days post-SE and animals in these cohorts were sacrificed 14 days after completing the BrdU injection series. Prior to sacrifice, vascular permeability was assayed serially at 7, 14, 21, 24 and 56 days post-SE, using gadolinium-diethylenetriaminepentaacetic acid (Gd-DTPA)-enhanced magnetic resonance imaging (MRI). HIf-1α and VEGF expression were assayed using single and double label immunohistochemistry (IHC). Endothelial proliferation and vascular density were assayed by single and double-label IHC for BrdU and von Willebrand factor. Results: Pathological angiogenesis was widespread but restricted to limbic and paralimbic structures, including hippocampus, amygdala, and piriform cortex. HIF-1α and VEGF expression in these regions was apparent by 1 and 3 days post-KASE, respectively, and remained chronically upregulated thereafter. Endothelial proliferation was dramatically increased (p < 0.01) during the first 14 days (day 1 and day 7 cohorts) post-SE and fell precipitously thereafter. Pathological neovascularization evolved between 21 and 35 days post-KASE and paralleled increases in BBB permeability within these regions. Conclusions: The evolution of pathological angiogenesis within limbic structures following KASE is initiated by hypoxia via the upregulation of HIF-1α and VEGF. These cytokines/growth factors stimulate endothelial proliferation and neovascularization within successive and relatively discrete time intervals. The resulting abnormal neovascular complexes appear to be the primary source of vascular leakage and persist within the chronically epileptic brain. Vascular pathogenesis may therefore present novel targets for antiepileptogenic/antiepileptic therapy.