Abstracts

VEGF, a growth factor normally expressed in glial and endothelial cells, promotes angiogenesis and has been demonstrated to be neuroprotective in experimental models of ischemia and epilepsy when exogenously applied to the hippocampus. Recently it has been observed that status epilepticus (SE) can induce the neuronal expression of VEGF in hippocampal and hypothalamic neurons. The neuronal expression of VEGF may contribute to its neuroprotective action. To further characterize the neuronal expression of VEGF after SE, we examined VEGF-immunroreactivity (IR) in the cortex of the rat after pilocarpine-induced SE. Pilocarpine (380mg/kg, s.c.) was injected into adult, male Sprague-Dawley rats 30min after pretreatment with atropine methylbromide (1mg/kg, s.c.). One hr after the onset of SE each animal received diazepam (5mg/kg, i.p.). Control animals (n=5) were treated in a similar fashion except saline was substituted for pilocarpine. All animals were perfusion-fixed with 4% paraformaldehyde 24hr (n=10) or 1 week (n=4) after SE. The brains were removed and cut on a vibratome. Free-floating sections (50[mu]) were incubated in antisera against VEGF (goat polyclonal, 1:500 dilution, R[amp]D Sys.) or Heat Shock Protein (HSP70, mouse monoclonal, 1:1000 dilution, Stressgen). Additional sections were slide mounted and processed for Fluorojade B or silver degeneration stain. VEGF-IR was observed in select neuronal populations within the cortex 24hr SE. Neurons in the middle layers of the sensory, and motor cortices stained positively for VEGF. In the cingulate, perirhinal, piriform and entorhinal cortices VEGF-IR was expressed in layer 2 and 4/5 neurons . The same neuronal populations that expressed VEGF-IR also expressed HSP-IR and stained positively for Fluorojade B 24hr after SE. One week after SE, VEGF-IR was still present in some cells but greatly diminished. There was no VEGF-IR in the cortical neurons of control animals. These results demonstrate that VEGF, a growth factor not normally expressed in neurons, can be induced in select populations of cortical neurons after SE. The observation that these neurons also express HSP and and stained positively for Fluorojade suggests that these neurons were stressed or injured. It is unclear whether the neuronal expression of VEGF contributes to its neuroprotective action observed after ischemia and seizures. It remains to be determined whether the neuroprotective action of VEGF is mediated through an activation of the Akt survival pathway. (Supported by The CURE Foundation, the New York State Department of Health and the Helen Hayes Hospital Foundation and NS37562.)