Abstracts

Neurotrauma produced by prolonged limbic status epilepticus (SE) results in the selective depletion of neurons in several limbic structures, accompanied by a pronounced gliosis. Following kainic acid induced SE, reactive astrocytes in these structures exhibit chronically upregulated expression of vascular endothelial growth factor (VEGF), and are intimately associated with apparent increases in microvascular density. Since VEGF is a potent promoter of angiogenesis in the adult brain, and is also known to increase microvascular permeability, we investigated whether these pathologies were present within these structures following SE. SE was induced in male wistar rats (250g [ndash] 350 g) by injection of kainic acid (10 mg/kg, i.v.), and was terminated four hours after its onset by injection of pentobarbital (20 mg/kg, i.p.). Separate cohorts were processed either for BrdU immunohistochemistry, to assay endothelial proliferation and angiogenesis, or for quantitative autoradiography (QAR) using radioiodinated serum albumin (¹²⁵I-RISA), to assay microvascular permeability. BrdU injections (50 mg/kg, i.p) were given for thirty consecutive days following termination of SE. Rats were perfused fourteen days later and processed for double-label immunohistochemistry for BrdU and vonWillebrand factor. QAR was performed eight weeks following the termination of SE. ¹²⁵I-RISA was administered (100 [micro]Ci/rat, i.v.) and allowed to circulate for 3 hrs, with arterial blood samples obtained at regular intervals. Rats were sacrificed immediately thereafter and their brains processed for QAR. Autoradiograms were subsequently analyzed using an AIS image analysis system for evidence of increased microvascular permeability. Endothelial cells positively labeled for BrdU were significantly increased (p [lt] 0.05) relative to control animals within limbic structures damaged by SE, and were commonly incorporated into the microvascular endothelium. QAR analysis revealed that microvascular permeability was also significantly increased (p [lt] 0.05) relative to control animals within these limbic structures. The regional distributions of angiogenesis and increased microvascular permeability were highly correlated. Chronic VEGF production by reactive astrocytes within the rat limbic system following SE contributes to the development of both angiogenesis and increases in microvascular permeability within these structures. Increased microvascular permeability in this context may derive exclusively from SE-induced neovascular capillaries, reflecting compromised blood-brain barrier integrity, or via more general effects of VEGF on microvascular permeability involving both mature and neovascular capillaries. In either case, the possibility exists that these pathologies may contribute directly to regional epileptogenesis.