Elsevier

Neuroscience

Volume 166, Issue 1, 10 March 2010, Pages 312-332
Neuroscience

Systems Neuroscience
Research Paper
Vascular changes in epilepsy: functional consequences and association with network plasticity in pilocarpine-induced experimental epilepsy

https://doi.org/10.1016/j.neuroscience.2009.12.002Get rights and content

Abstract

Angiogenesis and blood-brain-barrier (BBB) damage have been proposed to contribute to epileptogenesis and/or ictogenesis in experimental and human epilepsy. We tested a hypothesis that after brain injury angiogenesis occurs in the most damaged hippocampal areas with the highest need of tissue repair, and associates with formation of epileptogenic neuronal networks. We induced status epilepticus (SE) with pilocarpine in adult rats, and investigated endothelial cell proliferation (BrdU and rat endothelial cell antigen-1 (RECA-1) double-labeling), vessel length (unbiased stereology), thrombocyte aggregation (thrombocyte immunostaining), neurodegeneration (Nissl staining), neurogenesis (doublecortin (DCX) immunohistochemistry), and mossy fiber sprouting (Timm staining) in the hippocampus at different time points post-SE. As functional measures we determined BBB leakage (quantified immunoglobulin G (IgG) immunostaining), and hippocampal blood volume (CBV) and flow (CBF) in vivo (magnetic resonance imaging, MRI). The total length of hippocampal blood vessels was decreased by 17% at 2 d after status epilepticus (SE) induced by pilocarpine in adult rats (P<0.05 as compared to controls) which was not accompanied by alterations in hippocampal blood volume (BV) and flow (BF). Number of proliferating endothelial cells peaked at 4 d post-SE and correlated with an increase in vessel length (r=0.900, P<0.05). Vessels length had recovered to control level or even higher at 2 wk post-SE, angiogenesis being most prominent in the CA3 (128% as compared to that in controls, P<0.05), and was associated with increased BV (178% as compared to that in controls, P<0.05). Enlargement of vessel diameter in the hippocampal fissure was associated with thrombocyte aggregation in distal capillaries. BBB was most leaky during the first 4 d post-SE and increased IgG extravasation was observed for 60 d. Our data show that magnitude of endothelial cell proliferation is not associated with severity of acute post-SE neurodegeneration or formation of abnormal neuronal network. This encourages identification of molecular targets that initiate and maintain specific aspects of tissue reorganization, including preservation and proliferation of endothelial cells to reduce the risk of epileptogenesis and enhance recovery after brain injury.

Section snippets

Animals

Adult male Sprague–Dawley rats (Harlan, AD, Horst, Netherland) weighing 300–350 g were used. The rats were housed in a controlled environment (temperature 22±1 °C; humidity 50%–60%; lights on 0700–1900) with free access to food and water. Animal procedures were approved by the Animal Care and Use Committee of the University of Kuopio, Finland, and conducted in accordance with the guidelines set by the European Community Council Directives 86/609/EEC.

Induction of status epilepticus

Rats were injected s.c. with scopolamine (1

Distribution and density of EBA positive blood vessels in the hippocampus after SE

EBA is located in the endothelial cells on the luminal side of blood vessels (Ghabriel et al., 2002). Several studies have demonstrated that EBA is very unstable in injured brain with vascular damage (Sternberger et al., 1989, Rosenstein et al., 1992, Lin et al., 2001). Hence, it can be used as a sensitive indicator of BBB impairment.

Discussion

Previous studies have suggested that vascular density is increased after SE, and that damage to existing or leakiness of newly formed vessels results in extravasation of plasma proteins which contributes to epileptogenesis and ictogenesis (van Vliet et al., 2007, Seiffert et al., 2004). However, there have been no study that has investigated whether endothelial cells actually proliferate after SE, and what is the time course and magnitude of angiogenesis during epileptogenesis. Also,

Conclusion

Here we demonstrate that experimental SE has multiple effects on blood vessels, including early loss of immunolabeled vessels associated with BBB leakage and formation of thrombocyte clots. Vascular injury is followed by endothelial cell proliferation and angiogenesis which restores vascular length within 2 wk post-SE and increases CBV. The magnitude of vascular injury and consequent angiogenesis are not temporally or quantitatively related to formation of epileptogenic circuitry in the dentate

Acknowledgments

This study was supported by European CommissionEC FP6, MEST-CT-2005-019217, Academy of Finland, and the Sigrid Juselius Foundation.

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