Ionic behaviors and nerve growth factor dependence in developing chick ganglia: II. Studies with neurons of dorsal root ganglia☆

摘要

Usingintactdorsalrootganglia(DRG)fromembryonic(E)chickandmeasuring22Na+accumulation,theauthorshaverecentlyshownthat(i)ioniccontrolbythegangliahasacompleterequirementforexogenousNGFbetweenE6andE10,and(ii)controlofionpumpmechanismsindependentofexogenousNGFisprogressivelyacquiredbythesegangliafromE10toE16.Similarexperimentshavenowbeencarriedoutusingenrichedsuspensionsofganglionicneuronstotestwhethertheacquisitionofendogenouscontrolbyoldergangliawas(1)duetothecloseassociationbetweenneuronsandnonneurons,and(2)correlatedwithadecreasingneedbytheseneuronsforexogenousNGFforsurvivalinculture.Inthisenrichedneuronalpopulation,Na+accumulationintheabsenceofNGFincreasesfromE7toE10,parallelingtheincreaseinNa+accessiblespaceunderouabain,butthendecreasesconspicuouslybetweenE10andE16,despitelittlechangeintheouabain-sensitiveNa+space.NGFpreventsNa+accumulationduringtheearlyperiod,andbecomesincreasinglyirrelevantforthisbehaviorinlater(afterE10)development.K+movements(tracedwith86Rb+)behavedsimilarly.ActiveK+influx(Na+,K+-pumpmediated)alsoincreasesseveralfoldbetweenE7andE10.ThisK+influxissensitivetoNGFatE7andE10butnotatE14,parallelingtheobservedNa+andK+behaviors.ThesedatasuggestthatthecontrolofNa+,K+-pumpperformancesacquiredbytheseneuronsbetweenE10andE16representsthedevelopmentofaneuronalself-sufficiency.Thisincreaseinioniccontrolisnotduetoanincreaseinpumpmoleculesorpumpingefficiency.Noincreasesinthebindingof[3H]ouabainoractiveK+influxoccurbetweenE10andE16,whenioniccontrolisdeveloping.TheionicdependenceonNGFbytheDRGneuronschangeswiththeirdevelopmentalagealongthesametemporalpatterndisplayedbytheirsurvivalresponsetoNGFinculture.