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Vascular endothelial growth factor (VEGF) was first described as an angiogenic agent, but has recently also been shown to exert various neurotrophic and neuroprotective effects in the nervous system. These effects of VEGF are mainly mediated by its receptor, VEGFR-2, which is also referred to as the fetal liver kinase receptor 1 (Flk-1). VEGF is up-regulated in neurons and glial cells after epileptic seizures and counteracts seizure-induced neurodegeneration. In vitro, VEGF administration suppresses ictal and interictal epileptiform activity caused by AP4 and 0 Mg 2+ via Flk-1 receptor. We therefore explored whether increased VEGF signaling through Flk-1 overexpression may regulate epileptogenesis and ictogenesis in vivo. To this extent, we used transgenic mice overexpressing Flk-1 postnatally in neurons. Intriguingly, Flk-1 overexpressing mice were characterized by an elevated threshold for seizure induction and a decreased duration of focal afterdischarges, indicating anti-ictal action. On the other hand, the kindling progression in these mice was similar to wild-type controls. No significant effects on blood vessels or glia cells, as assessed by Glut1 and GFAP immunohistochemistry, were detected. These results suggest that increased VEGF signaling via overexpression of Flk-1 receptors may directly affect seizure activity even without altering angiogenesis. Thus, Flk-1 could be considered as a novel target for developing future gene therapy strategies against ictal epileptic activity.

Neuropeptide Y (NPY) gene transduction of the brain using viral vectors in epileptogenic regions can effectively suppress seizures in animals, and is being considered as a promising alternative treatment strategy for epilepsy. Therefore, it is fundamental to understand the detailed mechanisms governing the release and action of transgene NPY in neuronal circuitries. Using whole-cell recordings from subicular neurons, we show that in animals transduced by recombinant adeno-associated viral (rAAV) vector carrying the NPY gene, transgene NPY is released during high-frequency activation of CA1-subicular synapses. Released transgene NPY attenuates excitatory synaptic transmission not only in activated, but also in neighboring, non-activated synapses. Such broad action of transgene NPY may prevent recruitment of excitatory synapses in epileptic activity and could play a key role in limiting the spread and generalization of seizures.

To date, a variety of pharmacological treatments exists for patients suffering epilepsy, but systemically administered drugs offer only symptomatic relief and often cause unwanted side effects. Moreover, available drugs are not effective in one third of the patients. Thus, more local and more effective treatment strategies need to be developed. Gene therapy-based expression of endogenous anti-epileptic agents represents a novel approach that could interfere with the disease process and result in stable and long-term suppression of seizures in epilepsy patients. We have reported earlier that direct in vivo viral vector-mediated overexpression of the glial cell line-derived neurotrophic factor (GDNF) in the rat hippocampus suppressed seizures in different animal models of epilepsy. Here we explored whether transplantation of encapsulated cells that release GDNF in the hippocampus could also exert a seizure-suppressant effect. Such ex vivo gene therapy approach represents a novel, more clinically safe approach, since the treatment could be terminated by retrieving the transplants from the brain. We demonstrate here that encapsulated cells, which are genetically modified to produce and release GDNF, can suppress recurrent generalized seizures when implanted into the hippocampus of kindled rats.

Recently, hippocampal neuropeptide Y (NPY) gene therapy has been shown to effectively suppress both acute and chronic seizures in animal model of epilepsy, thus representing a promising novel antiepileptic treatment strategy, particularly for patients with intractable mesial temporal lobe epilepsy (TLE). However, our previous studies show that recombinant adeno-associated viral (rAAV)-NPY treatment in naive rats attenuates long-term potentiation (LTP) and transiently impairs hippocampal learning process, indicating that negative effect on memory function could be a potential side effect of NPY gene therapy.

Gene therapy-based overexpression of endogenous seizure-suppressing molecules represents a promising treatment strategy for epilepsy. Viral vector-based overexpression of the neuropeptide galanin has been shown to effectively suppress generalized seizures in various animal models of epilepsy. However, it has not been explored whether such treatment can also prevent the epileptogenesis. Using a recombinant adeno-associated viral (rAAV) vector, we induced hippocampal galanin overexpression under the neuron specific enolase promoter in rats. Here we report that in animals with galanin overexpression, the duration of electrographic afterdischarges was shortened and initiation of convulsions was delayed at generalized seizure stages. However, the hippocampal kindling development was unchanged. Short-term plasticity of mossy fiber-cornu ammonis (CA) 3 synapses was unaltered, as assessed by paired-pulse and frequency facilitation of field excitatory postsynaptic potentials (fEPSPs) in hippocampal slices, suggesting that despite high transgene galanin expression, overall release probability of glutamate in these synapses was unaffected. These data indicate that hippocampal rAAVbased galanin overexpression is capable of mediating anticonvulsant effects by lowering the seizure susceptibility once generalized seizures are induced, but does not seem to affect kindling development or presynaptic short-term plasticity in mossy fibers.

Kindling stimulations (1-millisecond duration square-wave pulses of 100 Hz delivered for 1 second) were given once daily at an initially sub-convulsive threshold current. The individual threshold was determined on the first days of kindling, by delivering stimulations of increasing current intensity in 10 µA steps, starting with 10 µA, until focal epileptiform activity (after-discharge) of at least 5-second duration was detected by electroencephalographic (EEG) recording. Behavioral seizures were scored according to the scale of Racine: 50 stage 0, no behavioral changes; stage 1, facial twitches; stage 2, chewing and head nodding; stage 3, unilateral forelimb clonus; stage 4, rearing, body jerks, bilateral forelimb clonus; stage 5, imbalance and falling (sideward or backward). EEG activity was recorded on a MacLab system 1 minute before, during, and at least 1 minute after the end of each after-discharge. Animals were considered fully kindled after having experienced five stage 5 seizures. Four weeks after termination of kindling, the after-discharge threshold was re-determined and animals were re-kindled using the same stimulation parameters as for initial kindling.

Kindling stimulations (1-millisecond duration square-wave pulses of 100 Hz delivered for 1 second) were given once daily at an initially sub-convulsive threshold current. The individual threshold was determined on the first days of kindling, by delivering stimulations of increasing current intensity in 10 µA steps, starting with 10 µA, until focal epileptiform activity (after-discharge) of at least 5-second duration was detected by electroencephalographic (EEG) recording. Behavioral seizures were scored according to the scale of Racine: 50 stage 0, no behavioral changes; stage 1, facial twitches; stage 2, chewing and head nodding; stage 3, unilateral forelimb clonus; stage 4, rearing, body jerks, bilateral forelimb clonus; stage 5, imbalance and falling (sideward or backward). EEG activity was recorded on a MacLab system 1 minute before, during, and at least 1 minute after the end of each after-discharge. Animals were considered fully kindled after having experienced five stage 5 seizures. Four weeks after termination of kindling, the after-discharge threshold was re-determined and animals were re-kindled using the same stimulation parameters as for initial kindling.

Recombinant adeno-associated viral (rAAV) vector-induced neuropeptide Y (NPY) overexpression in the hippocampus exerts powerful antiepileptic and antiepileptogenic effects in rats. Such gene therapy approach could be a valuable alternative for developing new antiepileptic treatment strategies. Future clinical progress, however, requires more detailed evaluation of possible side effects of this treatment. Until now it has been unknown whether rAAV vector-based NPY overexpression in the hippocampus alters normal synaptic transmission and plasticity, which could disturb learning and memory processing. Here we show, by electrophysiological recordings in CA1 of the hippocampal formation of rats, that hippocampal NPY gene transfer into the intact brain does not affect basal synaptic transmission, but slightly alters short-term synaptic plasticity, most likely via NPY Y2 receptor-mediated mechanisms. In addition, transgene NPY seems to be released during high frequency neuronal activity, leading to decreased glutamate release in excitatory synapses. Importantly, memory consolidation appears to be affected by the treatment. We found that long-term potentiation (LTP) in the CA1 area is partially impaired and animals have a slower rate of hippocampal-based spatial discrimination learning. These data provide the first evidence that rAAV-based gene therapy using NPY exerts relative limited effect on synaptic plasticity and learning in the hippocampus, and therefore this approach could be considered as a viable alternative for epilepsy treatment. © 2008 Wiley-Liss, Inc.

Gene therapy using recombinant adeno-associated viral vectors overexpressing neuropeptide Y in the hippocampus exerts seizuresuppressant effects in rodent epilepsy models and is currently considered for clinical application in patients with intractable mesial temporal lobe epilepsy. Seizure suppression by neuropeptide Y in the hippocampus is predominantly mediated by Y2 receptors, which, together with neuropeptide Y, are upregulated after seizures as a compensatory mechanism. To explore whether such upregulation could prevent seizures, we overexpressed Y2 receptors in the hippocampus using recombinant adeno-associated viral vectors. In two temporal lobe epilepsy models, electrical kindling and kainate-induced seizures, vector-based transduction of Y2 receptor complementary DNA in the hippocampus of adult rats exerted seizure-suppressant effects. Simultaneous overexpression of Y2 and neuropeptide Y had a more pronounced seizure-suppressant effect. These results demonstrate that overexpression of Y2 receptors (alone or in combination with neuropeptide Y) could be an alternative strategy for epilepsy treatment.

From the journal's beginning, this Editor has had the partnership of a Managing Editor who has made my job possible and contributed immeasurably to the success we have enjoyed. Angelica Kerr patiently taught me to use the Elsevier Editorial System and has upgraded my knowledge on a continuing basis principally by correcting my errors. She has also been the guardian of the review process by checking all manuscripts for their consistency with the published guidelines (in the front of each issue) and by informing the authors of their omissions in the most kind and courteous manner. Angelica has gently ridden herd on the review process with repeated reminders when reviewers were not rapidly responsive. All the Associate Editors must feel as I do about her unfailing willingness to listen to problems (or excuses) with patience and understanding. Because she has always been willing to help solve problems, the Editors have developed great respect and fondness for their interactions with her. I see this repeatedly in the letters that they exchange and on which I am copied. So, at this time, I must share my sadness with the entire Editorial Board as we announce that Angelica will be leaving us to take over as Content Development Manager of journals published by Elsevier within the fields of cardiology, dermatology, and clinical immunology. We will all miss having her available for so many issues, and I will miss her the most. She cannot be replaced, but she has launched us on a steady course that I believe we can sustain with some additional work. She has promised to remain available as a consultant for future problems. As she departed, I requested her counsel for our reviewers and potential authors, regarding matters that might speed the review process and improve the probability of favorable outcomes for manuscripts.