|Ph.D Student||Pachter Inbar|
|Subject||Network Dynamics during Seizure Initiation in an|
Acute Cortical Epilepsy Model: In-Vivo Two-Photon
Calcium Imaging Study
|Department||Department of Medicine||Supervisors||Professor Jackie Schiller|
|Professor Yitzhak Schiller|
|Full Thesis text|
Epilepsy is a prevalent disease affecting approximately 1% of the general population. In epilepsy the cortical network fluctuates between two fundamentally different activity states: the asymptomatic inter-ictal state and the symptomatic ictal state manifested as epileptic seizures. The manner by which the network undergoes the transition from the inter-ictal to the ictal state is largely unknown, despite the pathophysiological and clinical importance of this process.
In this work we used two-photon calcium imaging, which allows simultaneous recording from multiple neurons at a single cell resolution, in order to study the neocortical network dynamics during development of chemoconvulsant-induced seizures in-vivo in two models: 4-aminopyridine (4-AP) and picrotoxin.
Imaging was performed from layer 2-3 neurons in the S1 barrel cortex of Wistar rats. Neurons were bulk-loaded with the AM calcium dye Fluo-4 and seizures were induced by local application of either 4-AP or picrotoxin to the exposed cortical surface. For the need of this work an algorithm was developed in order to detect calcium signal events representing supra-threshold activity of the neurons. In addition, the local Electro-corticography was simultaneously recorded using extracellular electrodes.
Following application of both chemoconvulsants all animals developed electrographic seizures within the time of the experiment. In both models, prior to seizures emergence, during the pre-ictal phase, three major processes were detected: increase in the number of active neurons, gradual elevation of the firing rate, and changes in the network parameters implying enhanced synchrony.
The results show that changes in the neurons activity as well as network synchrony emerged minutes prior to the initiation of seizures, as determined electrophysiologically. These findings support the claim that seizures are not abrupt and un-predictable events as they were assumed to be for years, but rather a network phenomenon which develops over time until it ultimately manifests clinically and electrographically. These conclusions may aid the future development of new strategies to predict and eliminate seizures and eventually aid in development of novel treatment modalities for patients suffering from intractable epilepsy.