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Title

Topdowncontrolofspinalsensorimotorcircuitsessentialforsurvival

Authors

StellaKoutsikou1,2,RichardApps2&BridgetM.Lumb2

Affiliations1SchoolofBiologicalSciences,LifeSciencesBuilding,UniversityofBristol,U.K.2SensoryandMotorSystemsGroup,SchoolofPhysiology,Pharmacology&

Neuroscience,BiomedicalSciencesBuilding,UniversityofBristol,U.K.

RunningTitle

Midbraincontrolofsensoryandmotorsystems

Keywords

Periaqueductalgrey,Survival,Nociception,Spinalcord,Cerebellum,Freezing

behaviour,Descendingcontrol

Totalnumberofwords(excludingreferencesandfigurelegends)

1,962

CorrespondingAuthor

DrStellaKoutsikou

SchoolofBiologicalSciences,LifeSciencesBuilding(Office1.09),

24TyndallAvenue,UniversityofBristol,BristolBS81TQ

stella.koutsikou@bristol.ac.uk

Tel:(+44)1173941344or3941329

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AbstractTheabilitytointeractwithchallengingenvironmentsrequirescoordinationofsensoryandmotorsystemsthatunderpinappropriatesurvivalbehaviours.Allanimals,includinghumans,useactiveandpassivecopingstrategiestoreacttoescapableorinescapablethreatsrespectively.Acrossspeciestheneuralpathwaysinvolvedinsurvivalbehavioursarehighlyconservedandthereisaconsensusthatknowledgeofsuchpathwaysisafundamentalsteptowardsunderstandingtheneuralcircuitsunderpinningemotioninhumansandtreatinganxietyorotherprevalentemotionaldisorders.Themidbrainperiaqueductalgrey(PAG)liesattheheartofthedefence-arousalsystemanditsintegrityisparamounttotheexpressionofsurvivalbehaviours.Todate,studiesof‘topdowncontrol’componentsofdefencebehaviourshavefocusedlargelyonthesensoryandautonomicconsequencesofPAGactivation.Inthiscontext,effectsonmotoractivityhavereceivedcomparativelylittleattention,despiteoverwhelmingevidenceofapivotalroleforthePAGincoordinatingmotorresponsesessentialtosurvival(e.g.suchasfreezinginresponsetofear).InthisarticleweprovideanoverviewoftopdowncontrolofsensoryfunctionsfromthePAG,includingselectivecontrolofdifferentmodalitiesofsensory,includingproprioceptive,informationforwardedtoamajorsupsraspinalmotorcontrolcentre;thecerebellum.Next,evidencefromourownandotherlaboratoriesofPAGcontrolofmotoroutflow,isalsodiscussed.Finally,theintegrationofsensorimotorfunctionsbythePAGisconsidered,aspartofcoordinateddefencebehavioursthatprepareananimaltobereadyandabletoreacttodanger.Abbreviationsdl/lPAG,dorsolateral/lateralperiaqueductalgrey;dm,dorsomedial;l,lateral;PAG,periaqueductalgrey;vlPAG,ventrolateralperiaqueductalgreyIntroduction:RoleofperiaqueductalgreyinsurvivalDefencebehavioursessentialtosurvivalcanbeinnate,buttheycanalsobelearnt,andduringevolutionareconservedacrossspecies,includinghumans(Takahashi,1992b,a;Blanchardetal.,2001a;Blanchardetal.,2001b;Gross&Canteras,2012;LeDoux,2012).Themidbrainperiaqueductalgrey(PAG)sitsattheheartofthebraincircuitrythatcoordinatessurvivalbehavioursandhaslongbeenidentifiedasapivotalcomponentoftheso-called‘emotionalmotorsystem’(Holstegeetal.,1996).ThePAGsurroundsthecentralaqueductand,basedonpatternsofinternalandexternalconnectivityandonitscyto-andchemo-architecture,canbedividedintofourlongitudinalcolumns(dorsomedial(dm),dorsolateral(dl),lateral(l)andventrolateral(vl),seeFig.1),eachwithdistinctfunctionsinsurvivalbehaviour(Carrive,1993;Bandler&Shipley,1994;Behbehani,1995;Bandleretal.,2000;Keay&Bandler,2002;Tovoteetal.,2016;Watsonetal.,2016).

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Asafunctionalinterfacebetweenthelimbicstructuresessentialtosurvivaldefencebehaviours,suchasthecentralnucleusoftheamygdala,thehypothalamusandmedialprefrontalcortex(Anetal.,1998;Petrovichetal.,2001;Canteras,2002;Gross&Canteras,2012;LeDoux,2012;Linnmanetal.,2012),andthelowerbrainstemandspinalcord(Fig.2),thePAGplaysamajorroleinintegratingresponsestointernalandexternalthreats(Blanchardetal.,1981;Bandleretal.,2000;Sokolowski&Corbin,2012)thatmaximiseananimal’ssurvivalbygeneratingarepertoireofconditionedandunconditionedfearbehaviours(Bandleretal.,1985;Bandler&Depaulis,1991;Bandler&Shipley,1994;Depaulisetal.,1994;Chenetal.,2015;Dengetal.,2016;Tovoteetal.,2016).SurvivalbehavioursorchestratedbythePAGcanbecategorisedintoactiveandpassivecopingstrategies(Fig.1).Activecopingisevokedbyactivationofthedl/l-PAG,whereaspassivecopingistriggeredbyactivationoftheventrolateralcolumn.Activecopingstrategies(e.g.confrontation,fightorflight)areevokedifthestressorisescapable(e.g.briefacutepain,closeencounterwithapredator).Bycontrast,passivecopingstrategies(e.g.quiescence,recuperation,freezing)areelicitedifthestressorisinescapable(e.g.visceralpain,proximitytoorcapturebyapredator),thusfacilitatingrecoveryandhealingbutalsoviaidentifieddl/lPAG–vlPAGfunctionalexcitatoryconnections(Tovoteetal.,2016),preparingtheanimaltoreact/escapewhenopportunityarises.AkeycomponentofCNSstrategiesforeffectivedefencebehaviouristhetopdownmodulationofsensorytransmissioninthespinaldorsalhornand,sincetheoriginaldescriptionof‘stimulation-producedanalgesia’fromthePAG(Reynolds,1969)attentionhasfocusedondescendingpainmodulatorysystemsthatoriginateinthebrainstemandoperateatthelevelofthespinalcord.PeriaqueductalGrey:roleinsurvival-topdowncontrolofspinalsensoryprocessingThespinaldorsalhornisthelocationofthefirstsynapseinpainpathwaysandthecapacityforthePAGtofilteroutnociceptivetransmissionatthisearlystagehaslongbeenrecognisedasessentialfortheexecutionofsurvivalbehaviours,asitminimisesnociceptor-drivensensorydistractionandmotordisturbancesthatwouldotherwiseperturbeffectiveactions(Waters&Lumb,1997,2008).Inthiscontext,wenowknowthatthedescendingpainmodulatorysystem(DPMS)thatoriginatesfromd/dl-andvl-PAGdiscriminatesnotonlybetweenspinalprocessingoflowintensitymechanosensitiveinputsversushighintensity(nociceptive)inputsbut,importantly,betweennociceptiveinputsofdifferentbehaviouralsignificancei.e.thoseconveyedinA-versusC-nociceptors(Waters&Lumb,2008).Intheir2008paper,WatersandLumbprovidedmechanisticevidencethatdifferentialcontrolofA-versusC-fibre-evokedresponsesofdorsalhornneuronesfromboththeventrolateralanddorsolateral/lateralcolumnsofthePAGresultsfromthemodulationofspinalsegmentalinhibition.Fromabehaviouralperspective,A-andC-fibrenociceptorsconveydifferentqualitiesofthenociceptivemessage;well-localised,rapidlyconducted,‘prickingpain’thatistolerableversus

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poorlylocalised‘aching/burningpain’thatisslowlyconductedandcanbeintolerable.IthasbeenproposedthatsuppressionofC-fibremediatedpainandsimultaneousenhancementofA-fibremediatedpainhasimportantconsequencesinrelationtobothactiveandpassivecopingstrategiesasitwouldfilteroutunwanteddistractinginformationandleaveintact,orevenaugment,the‘useful’componentofthepainsignalthatcanprovidemotivationandguidance(Leithetal.,2007;Waters&Lumb,2008;Drakeetal.,2016).Thehypothesisthatdescendingcontrolofspinalsensoryprocessingactstofilteroutdistractinginformationenroutetosupraspinalmotorcontrolcentreshas,untilnow,beenbasedonindirectevidence.Recentlyhowever,CerminaraandcolleaguesprovidedevidencethatthePAGcanmodulatecerebellarresponsestosensoryinputs(Cerminaraetal.,2009)andthisfindingwassubsequentlyadvancedandrefinedinstudiesofPAGinfluencesonspinalprocessingofsensoryinputtopre-cerebellarpathways.MotorbehavioursessentialforsurvivalareguidednotonlybyinformationabouttheexternalenvironmentthatisprovidedbycutaneousmechanosensitiveandA-fibrenociceptiveinputs,butalsobyinformationfromtheinternalenvironment;inparticularproprioceptiveinformationthatsignalsbodypositionandmovement.Inthiscontext,ourrecentstudieshavemadetheimportantfindingthatthePAGenhancesproprioceptivetransmissioninspino-olivarypathways(Fig.3D),whichinturnforwardinformationtothecerebellum(Fig.3).Thecerebellumisthelargestsensorimotorstructureinthebrainand,assuch,behaviourallyrelevantselectivityindescendingcontrol,includingenhancementofresponsestoproprioceptiveinputs,demonstratethecapacityofthePAGtoregulatesensoryinputtosupraspinalmotorcontrolcentresand,asaconsequence,toensurethecoordinationofappropriatedefensivebehavioursinaversivesituationswhenthePAGbecomesactive.ItisclearthatthePAGcanselectivelycontrolsensoryinputtothebrainthatensurestheexecutionofappropriatebehaviours,butuntilrecently,thequestionofwhetherthePAGhasdirecteffectsonthemotorapparatusthatdrivesbehaviourremainedunanswered.PeriaqueductalGrey:roleinsurvival-topdowncontrolofmotorcircuitsDescendingcontrolfromthePAGisessential(Keay&Bandler,2001)toelicitmotorresponsescharacteristicofsurvivalbehaviours.However,littleisknownoftheneuralcircuitsthatmediatethediversityofbehaviouralresponsesassociatedwithPAGactivation(Fig.1).Thisisasignificantgapinourunderstandinggiventhesurvivalimportanceofinitiating,adaptingandmaintainingcoordinatedmotorresponsesinaversiveandthreateningsituations.Toelicitactiveorpassivemotorresponses,thePAGmustengageultimatelywithspinalmotorcircuitsand,importantlywehaverecentlyreportedfacilitationofα-motoneuroneexcitabilityfromthevlPAG(Koutsikouetal.,2014).TheseeffectscouldbemediatedbydirectprojectionsfromthePAGtothespinalventralhorn

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(Mouton&Holstege,1994)and/orindirectly(Mantyh,1983;Tovoteetal.,2016),includingviathecerebellum(Dietrichs,1983;Silleryetal.,2005).AcerebellarlinkissupportedbytheidentificationofanatomicalconnectionsbetweenthePAGandpre-motorstructuressuchasthelateralreticularnucleus(Rosteetal.,1985)andtheinferiorolive;thesolesourceofclimbingfibrestothecerebellum(Swenson&Castro,1983a,b;Rutherfordetal.,1984;Watsonetal.,2013;Koutsikouetal.,2014).Importantly,apowerfulphysiologicallinkbetweenthePAGandthecerebellumhasbeenidentifiedelectrophysiologically(Koutsikouetal.,2014).UnequivocalevidenceforatopdownPAG-cerebellarlinkinthecontrolofspinalmotoroutflowanddefencebehaviourisprovidedbyreportsthat:(i)powerfuldescendingfacilitatoryinfluencesfromthevlPAGonspinalα-motoneuroneexcitabilityisabolishedbycerebellectomyand(ii),targetedlesionsofcerebellarinput-outputpathwaysabolishesthevlPAG-inducedincreaseinα-motoneuroneexcitabilityanddisruptsinnateandfear-conditionedfreezingbehaviour(Koutsikouetal.,2014).However,itisnotknownhowpathwaysfromthePAGtothespinalcordthataredirectandindirect(suchasthosethatinvolvethecerebellum)mightinteracttoco-ordinatemotoroutflow.InadditiontoidentifyingnovelPAGcircuitswithsupraspinalmotorstructures,ourfindingsontopdowncontrolofmotorfunctionatthelevelofthespinalcordmayalsogeneratediscussion.Thisisbecause,atfirstsight,vlPAG-evokedincreasesinmuscletoneappearatoddswiththeclassicviewthatthevlPAGcoordinatespassivecopingstrategies,whichareassociatedwithquiescenceandwithdrawalfromtheenvironment.However,fearevokedfreezingfromthevlPAGiswelldocumentedand,tomaintainatenseposture,requiresincreasedmuscletoneasreportedhere(Misslin,2003).Furthermore,aneffectofvlPAGonα-motoneuroneexcitabilityisatoddswiththehypothesisthatincreasesinmuscletoneseeninfear-inducedfreezingbehavioursismediatedbyintra-PAGinhibitorymechanismsregulatedbytheventrolateralsector(Walker&Carrive,2003);ratherthanbyeffectsoftheventrolateralsectoronmotoroutflowassuggestedbyourrecentstudies(Koutsikouetal.,2014;Koutsikouetal.,2015)andthoseofTovoteandcolleagues(Tovoteetal.,2016).PeriaqueductalGrey:roleinsurvival-topdownintegrationofsensoryandmotorsystemsTodate,datageneratedinseparatestudiesprovideclearevidencethatthevlPAGisthesourceoftopdowncontrolofeithersensoryprocessingormotoroutflow.Importantly,inorderforthevlPAGtoexecuteitssurvivalroleeffectivelyrequiresthatneuronesinthisregionareabletointegratesensoryandmotorfunctionsinacoordinatedway,asevidencedbyourrecentfindings(Koutsikouetal.,2015).Inthesestudies,neuronalstimulationatindividualsitesinthevlPAGresultedinsuppressionofcerebellarsensorytransmission(inhibitionofperipheralnerve-evokedcerebellarcorticalfieldpotentials),accompaniedsimultaneouslybyfacilitationofspinalmotoroutflow(increasedα-motoneuroneexcitability,Fig.4);

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providingevidencethatthePAGactsonbothsensoryandmotorsystemssimultaneously.ConcludingremarksAsthegatekeeperofspinalsensorytransmissionduringaversivebehaviour,theabilityofthePAGtoexertselectivecontroloversensoryinformationofdifferentmodalities,andofdifferentbehaviouralsignificance,includingthattransmittedtomotorcontrolcentres,ispivotaltotheroleofthePAGinthecoordinationofbehavioursessentialforsurvival.Importantly,itisnowevidentthatselectivecontrolofsensoryprocessingmaybepartofanintegratedsystemwherebythePAGcanorchestratesensoryandmotorfunctionsthusenablingbehaviourstobeexecutedwiththeappropriatedegreeofprecisionandstrength,therebyassistingsurvival.ReferencesAnX,BandlerR,OngurD&PriceJL.(1998).Prefrontalcorticalprojectionsto

longitudinalcolumnsinthemidbrainperiaqueductalgrayinmacaquemonkeys.JCompNeurol401,455-479.

BandlerR&DepaulisA.(1991).Midbrainperiaqueductalgraycontrolof

defensivebehaviorinthecatandtherat.InThemidbrainperiaqueductalgraymatter:functional,anatomicalandneurochemicalorganization,ed.DepaulisA&BandlerR.PlenumPress,NewYork&London.

BandlerR,KeayKA,FloydN&PriceJ.(2000).Centralcircuitsmediating

patternedautonomicactivityduringactivevs.passiveemotionalcoping.BrainResBull53,95-104.

BandlerR,PrineasS&McCullochT.(1985).Furtherlocalizationofmidbrain

neuronesmediatingthedefencereactioninthecatbymicroinjectionsofexcitatoryaminoacids.NeurosciLett56,311-316.

BandlerR&ShipleyMT.(1994).Columnarorganizationinthemidbrain

periaqueductalgray:modulesforemotionalexpression?TrendsNeurosci17,379-389.

BehbehaniMM.(1995).Functionalcharacteristicsofthemidbrain

periaqueductalgray.ProgNeurobiol46,575-605.BlanchardDC,BlanchardRJ,LeeMC&WilliamsG.(1981).Taminginthewild

Norwayratfollowinglesionsinthebasalganglia.PhysiolBehav27,995-1000.

BlanchardDC,GriebelG&BlanchardRJ.(2001a).Mousedefensivebehaviors:

pharmacologicalandbehavioralassaysforanxietyandpanic.NeurosciBiobehavRev25,205-218.

BlanchardDC,HyndAL,MinkeKA,MinemotoT&BlanchardRJ.(2001b).Human

defensivebehaviorstothreatscenariosshowparallelstofear-and

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anxiety-relateddefensepatternsofnon-humanmammals.NeurosciBiobehavRev25,761-770.

CanterasNS.(2002).Themedialhypothalamicdefensivesystem:hodological

organizationandfunctionalimplications.PharmacolBiochemBehav71,481-491.

CarriveP.(1993).Theperiaqueductalgrayanddefensivebehavior:functional

representationandneuronalorganization.BehavBrainRes58,27-47.CerminaraNL,KoutsikouS,LumbBM&AppsR.(2009).Theperiaqueductalgrey

modulatessensoryinputtothecerebellum:aroleincopingbehaviour?EurJNeurosci29,2197-2206.

ChenS,ZhouH,GuoS,ZhangJ,QuY,FengZ,XuK&ZhengX.(2015).

OptogeneticsBasedRat-RobotControl:OpticalStimulationEncodes"Stop"and"Escape"Commands.AnnBiomedEng43,1851-1864.

DengH,XiaoX&WangZ.(2016).PeriaqueductalGrayNeuronalActivities

UnderlieDifferentAspectsofDefensiveBehaviors.JNeurosci36,7580-7588.

DepaulisA,KeayKA&BandlerR.(1994).Quiescenceandhyporeactivityevoked

byactivationofcellbodiesintheventrolateralmidbrainperiaqueductalgrayoftherat.ExpBrainRes99,75-83.

DietrichsE.(1983).Cerebellarcorticalafferentsfromtheperiaqueductalgreyin

thecat.NeurosciLett41,21-26.DrakeRA,LeithJL,AlmahasnehF,MartindaleJ,WilsonAW,LumbB&Donaldson

LF.(2016).PeriaqueductalGreyEP3ReceptorsFacilitateSpinalNociceptioninArthriticSecondaryHypersensitivity.JNeurosci36,9026-9040.

GrossCT&CanterasNS.(2012).Themanypathstofear.NatRevNeurosci13,

651-658.HolstegeG,BandlerR&SaperCB.(1996).Theemotionalmotorsystem.Prog

BrainRes107,3-6.KeayKA&BandlerR.(2001).Parallelcircuitsmediatingdistinctemotional

copingreactionstodifferenttypesofstress.NeurosciBiobehavRev25,669-678.

KeayKA&BandlerR.(2002).Distinctcentralrepresentationsofinescapableand

escapablepain:observationsandspeculation.ExpPhysiol87,275-279.

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KoutsikouS,CrookJJ,EarlEV,LeithJL,WatsonTC,LumbBM&AppsR.(2014).Neuralsubstratesunderlyingfear-evokedfreezing:theperiaqueductalgrey-cerebellarlink.JPhysiol592,2197-2213.

KoutsikouS,WatsonTC,CrookJJ,LeithJL,LawrensonCL,AppsR&LumbBM.

(2015).ThePeriaqueductalGrayOrchestratesSensoryandMotorCircuitsatMultipleLevelsoftheNeuraxis.JNeurosci35,14132-14147.

LeDouxJ.(2012).Rethinkingtheemotionalbrain.Neuron73,653-676.LeithJL,WilsonAW,DonaldsonLF&LumbBM.(2007).Cyclooxygenase-1-

derivedprostaglandinsintheperiaqueductalgraydifferentiallycontrolC-versusA-fiber-evokedspinalnociception.JNeurosci27,11296-11305.

LinnmanC,MoultonEA,BarmettlerG,BecerraL&BorsookD.(2012).

Neuroimagingoftheperiaqueductalgray:stateofthefield.Neuroimage60,505-522.

MantyhPW.(1983).Connectionsofmidbrainperiaqueductalgrayinthe

monkey.II.Descendingefferentprojections.JNeurophysiol49,582-594.MisslinR.(2003).Thedefensesystemoffear:behaviorandneurocircuitry.

Neurophysiologieclinique=Clinicalneurophysiology33,55-66.MoutonLJ&HolstegeG.(1994).Theperiaqueductalgrayinthecatprojectsto

laminaVIIIandthemedialpartoflaminaVIIthroughoutthelengthofthespinalcord.ExpBrainRes101,253-264.

PetrovichGD,CanterasNS&SwansonLW.(2001).Combinatorialamygdalar

inputstohippocampaldomainsandhypothalamicbehaviorsystems.BrainResBrainResRev38,247-289.

ReynoldsDV.(1969).Surgeryintheratduringelectricalanalgesiainducedby

focalbrainstimulation.Science164,444-445.RosteLS,DietrichsE&WalbergF.(1985).Aprojectionfromtheperiaqueductal

greytothelateralreticularnucleusinthecat.AnatEmbryol(Berl)172,339-343.

RutherfordJG,AndersonWA&GwynDG.(1984).Areevaluationofmidbrainand

diencephalicprojectionstotheinferioroliveinratwithparticularreferencetotherubro-olivarypathway.JCompNeurol229,285-300.

SilleryE,BittarRG,RobsonMD,BehrensTE,SteinJ,AzizTZ&Johansen-BergH.

(2005).Connectivityofthehumanperiventricular-periaqueductalgrayregion.JNeurosurg103,1030-1034.

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SokolowskiK&CorbinJG.(2012).Wiredforbehaviors:fromdevelopmenttofunctionofinnatelimbicsystemcircuitry.Frontiersinmolecularneuroscience5,55.

SwensonRS&CastroAJ.(1983a).Theafferentconnectionsoftheinferiorolivary

complexinrats:astudyusingtheretrogradetransportofhorseradishperoxidase.AmJAnat166,329-341.

SwensonRS&CastroAJ.(1983b).Theafferentconnectionsoftheinferiorolivary

complexinrats.Ananterogradestudyusingautoradiographicandaxonaldegenerationtechniques.Neuroscience8,259-275.

TakahashiLK.(1992a).Developmentalexpressionofdefensiveresponsesduring

exposuretoconspecificadultsinpreweanlingrats(Rattusnorvegicus).JCompPsychol106,69-77.

TakahashiLK.(1992b).Ontogenyofbehavioralinhibitioninducedbyunfamiliar

adultmaleconspecificsinpreweanlingrats.PhysiolBehav52,493-498.TovoteP,EspositoMS,BottaP,ChaudunF,FadokJP,MarkovicM,WolffSB,

RamakrishnanC,FennoL,DeisserothK,HerryC,ArberS&LuthiA.(2016).Midbraincircuitsfordefensivebehaviour.Nature534,206-212.

WalkerP&CarriveP.(2003).Roleofventrolateralperiaqueductalgrayneurons

inthebehavioralandcardiovascularresponsestocontextualconditionedfearandpoststressrecovery.Neuroscience116,897-912.

WatersAJ&LumbBM.(1997).Inhibitoryeffectsevokedfromboththelateral

andventrolateralperiaqueductalgreyareselectiveforthenociceptiveresponsesofratdorsalhornneurones.BrainRes752,239-249.

WatersAJ&LumbBM.(2008).Descendingcontrolofspinalnociceptionfromthe

periaqueductalgreydistinguishesbetweenneuronswithandwithoutC-fibreinputs.Pain134,32-40.

WatsonTC,CerminaraNL,LumbBM&AppsR.(2016).NeuralCorrelatesofFear

inthePeriaqueductalGray.JNeurosci36,12707-12719.WatsonTC,KoutsikouS,CerminaraNL,FlavellCR,CrookJJ,LumbBM&AppsR.

(2013).Theolivo-cerebellarsystemanditsrelationshiptosurvivalcircuits.Frontiersinneuralcircuits7,72.

AdditionalInformationSectionCompetingInterestsWeconfirmthattheauthorshavenoconflictsofinterest.AuthorContributionsExperimentalworkwascarriedoutinthelaboratoriesofBMLandRA,SchoolofPhysiology,Pharmacology&NeuroscienceatUniversityofBristol.

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1.conceptionordesignofthework–SK,BML,RA2.acquisition,analysis,orinterpretationofdataforthework-SK3.draftingtheworkorrevisingitcriticallyforimportantintellectualcontent–SK,BML,RA4.approvedthefinalversionofthemanuscript–SK,BML,RA5.agreetobeaccountableforallaspectsoftheworkinensuringthatquestionsrelatedtotheaccuracyorintegrityofanypartoftheworkareappropriatelyinvestigatedandresolved–SK,BML,RA6.allpersonsdesignatedasauthorsqualifyforauthorship,andallthosewhoqualifyforauthorshiparelisted–SK,BML,RA.FundingBiotechnology and Biological Sciences Research Council(BBSRC)BB/G012717/1FigureLegendsAuthorbiographyStellaKoutsikoucompletedherPhDinneurophysiologyin2004withSallyLawson,beforejoiningtheBristolSensoryandMotorSystemsResearchGroup.CurrentlysheisworkingwithSteveSoffeandAlanRobertsintheSchoolofBiologicalSciencesatBristol.BridgetLumbstartedherresearchcareerinBirminghamandmovedtoBristolinthe1980stopursueherinterestsinCNSmechanismsofacuteandchronicpain.BridgetbecameaProfessorofNeurosciencein2008.RichardAppsreceivedhisPhDinneurophysiologyfromBristolin1988,andbecameaProfessorofNeurosciencein2007.Hisresearchinterestsfocusonolivocerebellarcontributionstosensorimotorcontrol.Weshareacommoninterestinthepathwaysandmechanismsthatmodulatesensoryandmotorcircuitsthatcontributetosurvivalbehaviours.Ourcombinedresearchmethodologyincludesinsituwhole-cellpatchrecordingandinvivoelectrophysiological,behaviouralandneuroanatomicaltechniques.AbstractFigurePeriaqueductalgreytopdowncontrolofsensoryandmotorcircuitsSchematicillustrationofthedorsomedial(dm),dorsolateral(dl),lateral(l)andventrolateral(vl)neuronalcolumnsofthecaudalperiaqueductalgrey(PAG)exertingtheirdescendinginfluencesonspinalandsupraspinalsensoryandmotorcircuits.Key:effectsoftopdowncontrolonspinalneurones;red,inhibited;green,facilitatedandblue,noeffect.Figure1.MidbrainperiaqueductalgreycoordinatesemotionaldefensivebehavioursSchematicillustrationofthedorsomedial(dm),dorsolateral(dl),lateral(l)andventrolateral(vl)neuronalcolumnswithintherostral(topoffigure)tothecaudal(bottomoffigure)periaqueductalgrey(PAG).OverviewoftheemotionalcopingstrategiesassociatedwithactivationofdistinctcolumnsofthePAG.Thedorsal/lateralcolumnsandtheventrolateralcolumnofthePAGorchestrateactivevspassivecopingbehavioursrespectively.Activecopingincludesbehavioursthatare

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associatedwithwholebodymovements,hypertension,tachycardiaandageneralhyperexcitability.Bycontrast,passivecopingdescribesasetofbehavioursthataregenerallycharacterisedbylackofmovement(butnotnecessarilyflaccidbodypostures)anddecreasedresponsivenesstotheenvironment(e.g.fear-evokedfreezingmediatedbyvlPAGactivationassociatedwithtensebodypostures).Informationpresentedinthisfigurehasbeencollatedfromexperimentalworkonbothcatsandratsinthefollowingpublications:Bandler&Depaulis,1991,Bandler&Shipley,1994,Bandleretal.,2000,Gross&Canteras,2012andDengetal.,2016.Figure2.Midbrainperiaqueductalgreyinteractionswiththedescendinglimbicsystem.Schematicillustrationofthedorsomedial(dm),dorsolateral/lateral(dl/l)andventrolateral(vl)neuronalcolumnsoftheperiaqueductalgrey(PAG)connectionswiththelimbicsystem.Efferentsfromtheamydala,hypothalamusandprefrontalcortextargetthePAGand,inturn,efferentsfromthePAGcontributetothedescendinglimbicsystemthattargets,medulla,pons,cerebellumandspinalcord.LA,lateralamygdala;BMA,basomedialamygdala;MeA,medialamygdala;BLA,basolateralamygdala;CeA,centralamygdala.Informationpresentedinthisfigurehasbeencollatedfromthefollowingpublications:An,etal.,1998,Gross&Canteras,2012,Linnmanetal.,2012,Koutsikouetal.,2014andTovoteetal.,2016.Figure3.Periaqueductalgreyselectivelyaltersspino-olivaryneuronalresponsestodifferentqualitiesofsensoryinput.A,Typicalexampleoftheresponseofaclass2neurontonoxiouspinch(3.6N):peristimulustimehistogram(PSTH,spikesper1sbin)areshownbefore(pre-PAG)andduring(PAG)vlPAGchemicalexcitationwithDL-Homocysteicacidintheanaesthetisedrat.DottedhorizontallineineachofthePSTHsindicatestheonsetanddurationoftheperipheralstimulus.B,SameasAexceptexampleclass2neuronresponsetoinnocuouspressure(0.5N).C,SameasAexceptexampleofclass3neuronresponsetonoxiouspinch(3.6N).D,SameasAexceptexampleofclass4neuronresponsetoinnocuousanklejointmanipulation.E,StandardtransversemapsoftheleftPAGatthreerostrocaudallevelstoshowhistologicalreconstructionofinjectionsites.Coordinatesarerelativetobregma.DM,Dorsomedial;DL,dorsolateral;L,lateral;VL,ventrolateral.Greenindicatesclass2(noxiouspinch);greenwithblackoutline,class2(noxiouspinchandinnocuouspressure);red,class3;blue,class4.AdaptedwithpermissionfromKoutsikouetal.2015.Figure4.Periaqueductalgreyactivationresultsinsimultaneousmodulationof(A)ascendingtransmissiontothecerebellumand(B)spinalmotorcircuits.A,Exampleofaveragedclimbingfibrefieldpotentials(CFPs)recordedfromthesurfaceofthecerebellarcortexintheanaesthetizedrat(C1zoneofleftcopulapyramidis).B,ExamplesofaveragedM-wave(M)andH-reflex(H)responses,thelatterindicativeofα-motoneuroneexcitability,recordedfromtheleftplantarismuscleatthesametimeasA.Allresponseswereevokedbyelectricalstimulationoftheipsilateraltibialnerve(<1mA).Eachaveragedexampleconsistsoffiveconsecutiveresponsesbefore(prePAG)andduring(PAG)vlPAGchemicalexcitationwithDL-Homocysteicacid(DLH).Arrowsindicateonsetoftheelectricalstimulus.C,

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StandardtransversemapsoftheleftPAGtoshowinjectionsitesofDLHinthevlPAG(filledcircles),fromwhichtheeffectsofvlPAGactivationonpeak-to-peakamplitudeofM-waveandH-reflexandCFPweretested.Thecoordinatesarerelativetobregma(DM,dorsomedial;DL,dorsolateral;L,lateral;VL,ventrolateral).AdaptedwithpermissionfromKoutsikouetal.2015.