Calcium Signaling in a Model of Temporal Lobe Epilepsy

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DESCRIPTION (provided by applicant): Temporal lobe epilepsy (TLE), a devastating seizure disorder that is difficult to control with anticonvulsant drugs, often develops following an initia insult to the CNS. In order to better understand the process of epileptogenesis and to develop innovative therapeutic approaches for the management of TLE, animal models have been developed that exhibit some of the hallmarks of this seizure disorder: a period of status epilepticus (SE) which serves as the initial insult to the CNS, a variable latent period during which seizures do not occur, and the eventual development of recurrent, spontaneous seizures of temporal lobe origin. Recently we used the kainic acid (KA) model of TLE to investigate 'reactive' astrocytes in the hippocampus (HC), a brain region known to be involved in seizure generation. There is a significant increase in gap junction coupling between astrocytes following KA-induced status epilepticus (SE). Therefore, the astrocytic network architecture is altered in brain regions associated with seizure generation. We also discovered that astrocytes express kainate receptor (KAR) subunits following SE and hypothesize that activation of KARs can result in calcium (Ca2+) transients that induce the release of signaling molecules that modulate neuronal activity in the HC. The present application will use targeted path scanning 2-photon microscopy (TPS) to simultaneously evaluate rapid Ca2+ transients in large networks of astrocytes in brain slices obtained from animals treated with KA to induce SE. We employ in utero electroporation to target a genetically encoded Ca2+ indicating protein (Lck- GCaMP3) to the rat HC so that we can use brain slices obtained from adult animals to determine 1) if activation of KARs induces somatic Ca2+ signaling in networks of reactive astrocytes in the HC and 2) if KAR- induced and/or other agonist-induced Ca2+ signaling in the fine processes of reactive astrocytes induces the release of signaling molecules that directly influence network activity in HC brain slices obtained from KA- treated rats during both the latent period and chronic epilepsy. Finally, we will use electron microscopy to determine if there are ultrastructura changes in KAR expression, gap junction coupling, and dendritic ensheathment in the astrocyte compartment of the tripartite synapse of the CA1 and CA3 regions of the HC following KA-induced SE. The combined use of TPS with the stable expression of Lck-GCaMP3 in cells of the HC is a technical achievement that will contribute to our understanding of the functional role of KAR expression in astrocytes following status epilepticus (SE), both in the latent period and in chronic epilepsy. The proposed experiments will also determine how pathologic glial/neuronal interactions, both structural and functional, influence circuit activity during the development and persistence of epilepsy. Finally it is anticipated that the proposed experiments will lead to the identification of novel molecular targets for innovative therapeutic approaches for the treatment, prevention, and/or cure of this devastating seizure disorder.