TemporalLobeEpilepsy(TLE)isthemostfrequenttypeofpost-traumatic epilepsy,causingsignificantmorbidityintheveteranpopulation.Approximately60%ofadultepilepsycases areduetoTLE,whichisoftenmedication-resistantrequiringsurgery.Evenaftersurgery,~30%ofpatients continuetohaveictalevents.TLEcausescognitivedeficits,includingsignificantexecutive,memory,and neuropsychiatricdysfunction.Afterinitiationbyaprecipitatingevent,aseizure-free?epileptogenic?period typicallyfollowsbeforeTLEsetsin.Thenetworkmechanismsthatleadtothedevelopmentofepilepsyduring this?epileptogenic?periodarepoorlyunderstood.Adeepandpreciseunderstandingofthesemechanismsis criticalfordevelopingnew,moreeffective,methodsofinterventiontotreattemporalepilepsywithouttheside- effectsofmedicationsandthepotentialdisabilityoflargesurgicalresections. TLEseizuresarethoughttobeinitiatedatarestrictedtemporalfocusandthenentraincorticalnetworks.Recent evidencesuggeststhatalargenetworkofareas,includingneocortex,playanactiveroleinTLE.Sheybanietal. [7]reportsthataself-sustainedepilepticnetworkdevelopedduringepileptogenesis,becominggraduallyableto generate pathological electrical activity independent of the initial hippocampal focus. Together with other experimentalandclinicalobservations,thisstronglysuggeststhatextra-hippocampalcorticalareasareinvolved inepileptogenesis.However,howcorticalcircuitsgetmodifiedduringepileptogenesisremainsunknown. We combine chronic, in-vivo, large-field (Mesoscopic) two-photon microscopy with optogenetic modulation of specific cortical interneuron classes to study at single-cell resolution: i) how aberrant activity emerges in neocortical circuits over the course of epileptogenesis in the pilocarpine model of TLE, and ii) whether it is possible to interrupt the hippocampo-cortical cycle of epileptic activity by modulating optogenetically specific types of cortical interneurons.We hypothesize that hypersynchronous firing ofparvalbumin positive(PV+)and progressivelydecreasedengagementofSST+interneuronsemergesincorticalcircuitsduringtheepileptogenic period. Pathological circuit dynamics will be particularly observed during the 200-400 Hz high frequency oscillations(HFOs)showntobeamarkerforcircuithyper-excitability.
In aim1, wemeasurehowtheprofileofrecruitmentofdifferenttypesofcorticalneuronsduringhighfrequency oscillations (HFOs) changes as a function of time during epileptogenesis in the pilocarpine model of TLE. We expectthatovertimecorticalexcitabilitywillincreaseandautonomoushyper-synchronousactivitypatternsthat maybehippocampallyindependentwillemerge.
In aim2, wewillusesingle-photonoptogeneticswithstabilized step-function opsins as well as spatial-light-modulated (SLM), 2-photon, single-cell-specific optogenetics to causally interrogate cortical circuit excitability during epileptogenesis. Information obtained will be critical for identifyingcellspecifictargetsforinterventionstopreventepileptogenesisanditscognitivesequelaeinTLE. Overall Strategy: The overall goal of our collaborative merit proposal is to determine the key changes in hippocampalandneocorticalcircuitrythatpromotesthedevelopmentofepilepsyandcognitivedysfunctionafter the initial insult.
Aims of Other Proposals: 1. Wasterlain will use immunocytochemical techniques, including EMimmunocytochemistry,toquantifychangesintheGABAreceptorexpressionatthesynapseandintheperi- synaptic space. 2. Naylor will use in-vitro slice patch clamp recordings, optogenetics, and computational modeling to understand how the functional connectivity of different interneuron types changes during this key period.3.Golshaniwilluseacombinationofelectrophysiologicalandimagingtechniquestounderstandhowthe activitypatternsofdefinedinterneurontypesstudiedbyNaylorchangeinvivoduringtheepileptogenesisinthe hippocampus.Allstudiesareindependent,yetdeeplyinformeachother,asamulti-dimensionalunderstanding willbekeyformakingprogressinthishighlycomplexanddisablingdisorder.
Approximately60%ofadultepilepsycasesareduetoTemporalLobeEpilepsy(TLE).TLEisthemostfrequent typeofpost-traumaticepilepsy,causingsignificantmorbidityintheveteranpopulation.Itisoftendrug-resistant requiringsurgery.Evenaftersurgery,20-30%ofpatientscontinuetohaveictalevents.TLEseizuresentrain corticalnetworks,causingcognitivedeficitsthatincludeexecutive,memory,andneuropsychiatricdysfunction. Afterinitiationbyaprecipitatingevent,aseizure-free?epileptogenic?periodtypicallyfollowsbeforeTLepilepsy setsin.Howcorticalandhippocampalcircuitsgetmodifiedduringthisepileptogenicperiodremainsunknown. Here,wecombinestate-of-theart2-photonimagingandoptogenetictechniquestostudyhowhyperexcitability emergesinneocorticalcircuitsduringepileptogenesisinthepilocarpinemodelofTLE,andtoidentifypossible waystoreverseitbymodulatingtheactivityofspecificcelltypes.Informationobtainedwillbecriticalfor identifyingcell-specifictargetsforinterventiontopreventepileptogenesisanditscognitivesequelaeinTLE.
