Chemical synapses on semiconductor chips [Elektronische Ressource] / Rahul Alexander Kaul

Description

Technische Universit¨at Munc¨ henFakult¨at fur¨ PhysikMax-Planck-Institut fur¨ BiochemieAbteilung Membran- und NeurophysikChemical Synapseson Semiconductor ChipsRahul Alexander KaulVollst¨andiger Abdruck der von der Fakultat¨ fur¨ Physik der TechnischenUniversit¨at Mun¨ chen zur Erlangung des akademischen Grades einesDoktors der Naturwissenschaftengenehmigten Dissertation.Vorsitzender: Univ.-Prof. Dr. Manfred KleberPrufer¨ der Dissertation: 1. Hon.-Prof. Dr. Peter Fromherz2. Univ.-Prof. Dr. Andreas BauschDie Dissertation wurde am 05.02.2007 bei der Technischen Universitat¨ Munc¨ heneingereicht und durch die Fakultat¨ fur¨ Physik am 08.03.2007 angenommen.AbstractThe nervous system’s computational power largely depends on its interconnectivity.Chemicalsynapsesbetweenindividualneuronsrepresenttheminimalcomputationalunits of the brain. Interfacing single chemical synapses with semiconductor devicesto control and monitor their activity non-invasively would provide a tool to under-stand the dynamics underlying neuronal network function.Thisthesisprojectevolvedaroundallaspectsofneuron-semiconductorhybridsfromsynaptically connected cell-cell to cell-chip interactions. A complete experiment - aso-called loop - would consist of chip driven stimulation of the presynaptic cell, thetriggering of synaptic transmission, and the recording of postsynaptic activity bychip.

Informations

• Publié par: technische_universitat_munchen
• Publié le: 01 janvier 2007
• Nombre de lectures: 31
• Poids de l'ouvrage: 6 Mo

Extrait

TechniscFheakult¨Uanitvf¨urersit¨PhatysMik¨unchen

AbteilungMax-PlancMembrak-Institutn-fund¨urBNeuroiocphhemieysik

SynapsesicalChemonSemiconductorChips

RahulAlexanderKaul

Vollst¨Univandigersit¨aertAMb¨undrcucheknderzurvEornlanguderFngakultdes¨atakf¨urademiscPhysikhenderGraTecdeshnisceineshen

DoktorsderNaturwissenschaften

genehmigtion.Dissertaten

Vorsitzender:Univ.-Prof.Dr.ManfredKleber
Pr¨uferderDissertation:1.Hon.-Prof.Dr.PeterFromherz
2.Univ.-Prof.Dr.AndreasBausch

DieDisseingereicerthtationundwurdedurchamdie05F.02akult.200¨at7f¨bureiPhderysTikecamhnisc08.0hen3.20Univ07aersit¨atngenommen.M¨unchen

acttrAbs

Thenervoussystem’scomputationalpowerlargelydependsonitsinterconnectivity.
Chemicalsynapsesbetweenindividualneuronsrepresenttheminimalcomputational
unitsofthebrain.Interfacingsinglechemicalsynapseswithsemiconductordevices
tocontrolandmonitortheiractivitynon-invasivelywouldprovideatooltounder-
standthedynamicsunderlyingneuronalnetworkfunction.
Thisthesisprojectevolvedaroundallaspectsofneuron-semiconductorhybridsfrom
synapticallyconnectedcell-celltocell-chipinteractions.Acompleteexperiment-a
so-calledloop-wouldconsistofchipdrivenstimulationofthepresynapticcell,the
triggeringofsynaptictransmission,andtherecordingofpostsynapticactivityby
chip.Thechipsfeaturedtwo-waycontactstocontrolandmonitorthesesmallneu-
ronalnetworks:Electrolyte-Oxide-Semiconductor(EOS)capacitorsforstimulation
andfield-effecttransistors(FETs)forrecording.
Atthesinglecelllevel,the100µmlarge,identifiedneuronsfromLymnaeastagnalis
ledtoextracellularelectricalsignalsuptotensofmillivoltsduetotheirincreased
adhesionareacomparedtomammalianneurons.Closecontacttothechipverified
throughcell-substratedistancemeasurementscontributedtotheincreasedsignal
amplitudes.Ontheotherhand,theusageoftheartificialcell-adhesionmolecule
poly-L-lysinediminishedneuronalexcitabilitycausingoscillatingpatternsofactivity
andquiescence.Theintroductionoftwonovelartificialcelladhesionmolecules
allowedcellcultureofchemicalsynapsesonchipwithoutoscillatorybehavior.
Recentresultsdemandedacomparisonbetweenrampandsquarepulsestimulifor
thestimulationofpresynapticactivity.Tocreatecellularactivityonchipscoated
withathinSiO2layer,repetitiveburstsofmultiplesquare-shapedpulsesprovedto
bethemostreliableminimalinvasivemethod.
ThethreesnailneuronsVD4,LPeD1,andRPeD1formedgroupsofneuronalpairs
interconnectedviaexcitatoryorinhibitorysynapsesonchip.Theactivityofboth
typesofsynapsescouldbetriggeredandmonitoredthroughchipstimulationand
recording.AspecificpulseprotocolpotentiatedtheexcitatorysynapseVD4-LPeD1
todemonstratechipinducedandsupervisedneuronallearning.
Whilestudyinginhibitionasafunctionofadecreaseinpostsynapticfiringrate,chip
inducedstimulationofpostsynapticRPeD1completelypreventedsynapticinhibition
throughpresynapticcellVD4.
Achipcontrolleddoubleloopexperimentwithoneexcitatoryandoneinhibitory
synapsebetweenVD4-LPeD1andVD4-RPeD1provedthetechnique’sscalability.
Thissemiconductorchiptechnologythereforeprovidesatoolforsimultaneousob-
servationandcontrolofmultineuronalnetworkdynamicsattheresolutionofsingle
.cellsenerv

ii

Contents

1Introduction

2

2MaterialsandMethods12
2.1CellCulture................................13
2.1.1Lymnaeastagnalis,ModelAnimalforCellCultureofIndivid-
ualCentralNeurons.......................13
2.1.2PrerequisitesforCellCultureofChemicalSynapses......14
2.1.3ExtractionofIdentifiedGiantNeurons.............17
2.2ElectronicInterfacing...........................22
2.2.1Electrophysiology.........................22
2.2.2Chips...............................22
2.2.3Electronics.............................26
2.3Cell-SubstrateDistanceMeasurement..................31
2.4One-CompartmentModel........................33
2.4.1ExplanationoftheModel....................33
2.4.2ConsequencesforStimulation..................34
2.4.3ConsequencesforTransistorRecording.............37

3Results&Discussion40
3.1SingleCellObservations.........................41
3.1.1SingleCellRecording.......................41
3.1.2SingleCellStimulation......................55
3.2PairsConnectedviaanExcitatoryChemicalSynapse.........66
3.2.1TheExcitatoryLoopVD4-LPeD1................67
3.2.2PotentiationviaChipStimulation................70
3.2.3InvestigationofSinglePostsynapticPotentialswithTransistors70
3.2.4Summary-ExcitatorySynapses.................73
3.3PairsConnectedviaanInhibitoryChemicalSynapse.........75
3.3.1TheInhibitoryLoopVD4-LPeD1................75

iv

CONTENTS

3.3.2TheInhibitoryLoopVD4-RPeD1................77
3.3.3DoubleStimulationVD4andRPeD1..............79
3.3.4Summary-InhibitorySynapses.................83
3.4CellTripleswithTwoChemicalSynapses................86
3.4.1AnExcitatory-InhibitoryDoubleLoopLPeD1-VD4-RPeD1..87
3.4.2Summary-TripleswithtwoChemicalSynapses........89

4Summary&Outlook94
4.1Summary.................................95
4.2Outlook..................................96

endixApp

98

ACellCulture98
A.1AnimalPreparation............................98
A.2CellCultureMedia............................101
A.2.1NormalandAnti-BioticSaline..................101
A.2.2DefinedMedium(DM)andHigh-OsmolarityDM.......102
A.2.3Brain-ConditionedMedium...................102
A.3ChipConditioning............................104

BChipPost-Processing

CFLICStainingProtocol

051

061

DChemicals&Equipment107
D.1CellCultureMedium...........................107
D.2Preparation................................107
D.3ElectrophysiologyandSynapticBlock..................108
D.4ChipStimulationandRecording.....................108

v

1pterCha

Introduction

2

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”ChemicalSynapsesonSemiconductorChips”-adescriptioninspiringtheimag-
inationofscientistsandfictionauthorsalike.Thinkingaboutitsmeaning,the
firstpictureappearingbeforetheinnereyelookslike”Connectingthebraintothe
.computer”Takingacloserlookatanenvisionedbrain-computerlink,wesee,itcanwork
bothways.Eitherthecomputercommunicateswiththebrain,orthebrainwith
thecomputer.Thebrainreceivesinputsandcreatesoutputsmediatedthrough
sensorsandactuators,whichhelptoperceivetheenvironmentandtocreatephysical
interactions-like,forexample,focusingonasoccerballwithaneyewhilemoving
tokickapass.Howdoesthecomputerfitintothisscheme?
Althoughourimaginationcouldspreadwingsandenvisionitsinterplayeverywhere
-replacingdefunctsensoryorgans,bridgingdamagedneuronalcontactsoreven
movingartificiallegs-today’sresearchhastostaydowntoearthtomakethevery
efforts.wlingcrabasicfirstButwhatisitreallyabout?Whatarethetopicsactuallyinvestigatedintoday’s
scientificlabs?Andhowdotheyrelatetotheideasmentionedabove?Undoubtly
thisthesiswillnotreportonthecreationofartificialeyesorlimbs-theyseemtoo
muchfictiontobetrue.Sodoscientificfactsexisttobolstertheseideas?
Ofteninvestors,scientificallyaptamateursorthemediaask:’Whatcanyoudo
withthiskindofresearch?’Dependingontheinquirer’sinterest,wecanprovide
onetoallofthethreepossibleanswers:biosensorics,creatingatoolforneuroscience
researchorworkingoncomputationalaspectsofcell-chipinteractions.Duringthe
reply,onecanactuallyfeeltheimaginativestraintheaudiencethengoesthrough
tostretchatleastoneofthegivenanswerstofittheirownideasabout”Chemical
SynapsesonSemiconductorChips”.
Let’sstartwithwhatitisallabout,beforepaintinganill-fittingorevenmisleading
picture.Weextractbiologicaltissueandputitonelectronicdevicescreatedfromthesemi-
conductingmaterialsilicon:Sonotchipinthebrain,butbrainonachip.The
biologicalmaterialinvestigatedinthisthesisproject,wastakenfromananimal
modelforneuronalinteractionsincellculture,thesweetwatersnailLymnaeastag-
nalis.Sotherearenohumancyborgs,butmaybewecancreaterobo-snails?
Theanswerisno,sinceindividualneuronsareplacedonsmallsemiconductorde-
vicesonthechipinclosecontacttoeachother.Eventhoughwholeanimalsare
involvedintheprocessofextractingthenervecells,onlysinglecellsgetintouch
hip.cthewithDuringovernightincubationcellsstayonthechip,achemicalsynapse,thebasic
neuronalcell-cellcontact,formsbetweengroupsoftwonervecells.Toprotectthe
electronicsfromthesaltsolution-theelectrolyte-neededforthesurvivalofthe
nervecells,athinlayerofsilicondioxide,commonlyknownasglass,coversthe
semiconductingmaterial.Thisoxidelayerhasathicknessof10nanometers.

3

CHAPTER1.INTRODUCTION

Figure1.1:Nervecellsonsemiconductorchips.

(a)Asituationtypicalfortheresearchpresentedinthisthesis:Amicrographwitha
topviewonagroupof2nervecellsinclosecontacttoeachother.Thepicturewastaken
after16hoursincellcultureonasemiconductorchip.Afterthistimeachemicalsynapse
fosmramlledfrbameetweonenththeetleftwohandneurons.sideOshonwthsethechipgatetwoG,thestructuresvoltage-havesenbsoeenrohftheighlighfited:eld-effThecte
transistor:agatevoltagechangeduetonervecellactivitymodulatesthecurrentthatruns
betweensourceSanddrainD.Thelargeframeontherighthandsideencirclesthecapacitor
padCusedforstimulationofsinglenervecells.
(b)Aschematicsideviewofthesituationdepictedin(a):thearrowsindicatesignalflow
durin