Placodal sensory neurons in culture: Nodose ganglion neurons are unresponsive to NGF, lack NGF receptors but are supported by a liver-derived neurotrophic factor☆

摘要

Explantanddissociatedneuron-enrichedculturesofnodoseganglia(inferiorordistalsensoryganglionoftheXthcranialnerve)wereestablishedfromchickembryostakenbetweenembryonicDay4(E4)andDay16(E16).Theresponseofeachtypeofculturetonervegrowthfactor(NGF)wasexaminedoverthisdevelopmentalrange.Attheearliestagestaken(E4a€“E6),NGFelicitedmodestneuriteoutgrowthfromganglionexplantsculturedincollagengelfor24hr,althoughtheeffectofNGFongangliatakenfromE4chickswasonlymarginallygreaterthanspontaneousneuriteextensionfromcontrolgangliaofthesamedevelopmentalage.TheresponseofnodoseexplantstoNGFwasmaximalatE6a€“E7,butdeclinedtoanegligiblelevelingangliatakenfromE9a€“E10orolderchickembryos.Indissociatedneuron-enrichedcultures,nodoseganglionneuronswereunresponsivetoNGFthroughouttheentiredevelopmentalagerangebetweenE5andE12.IncontrasttothelackofeffectofNGF,upto50%ofnodoseganglionneuronssurvivedandproducedextensiveneuritesindissociatedcultures,oneithercollagen-orpolylysine-coatedsubstrates,inthepresenceofextractsoflateembryonicorearlyposthatchedchickliver(E18a€“P7).AntiserumtomouseNGFdidnotblocktheneurotrophicactivityofchick(orratorbovine)liverextracts.WhetherculturedwithchickliverextractaloneorwithchickliverextractplusNGF,nodoseganglionneuronstakenfromE6a€“E12chickembryosandmaintainedinculturefor2daysweredevoidofNGFreceptors,asassessedbyautoradiographyofculturesincubatedwith125I-NGF.Undersimilarconditions70a€“95%ofspinalsensoryneurons(dorsalrootgangliona€”DRG)wereheavilylabeled.IncontrasttothelackofNGFreceptorsonplacode-derivedneurons,thesatellitecellsoftheearly(E5a€“E8)nodoseganglion,whichareneural-crestderived,werefoundtopossessNGFreceptors.Weconcludefromthisstudythatsensoryneurons,suchasthoseofthenodoseganglion,derivedfromneurogenicplacodeshaveneurotrophicgrowthfactorrequirementswhicharedistinctfromthoseofneural-crestderivedsensoryneurons.WeproposethatthemodestfiberoutgrowththatNGFelicitsfromexplantsofnodosegangliatakenfromE4a€“E8chickembryosisnotaresponseofplacodalneuronsbutisindicativeofthederepressionandexpressioninvitroofneuronalpotentialitiescontainedwithintheneural-crestderivedcellsthatnormallygiveriseonlytothesatellitecellsofthenodoseandothercranialsensoryganglia.