The influence of VIIth and VIIIth cranial nerve roots upon the differentiation of Mauthner's cell in Ambystoma☆

[摘要] TheprimordiumoftheVIIIthcranialganglion(oticvesicle)wasextirpatedontherightsideof428embryosofAmbystomamaculatumatstage27.Mauthner'scell(MC)developsincloseassociationwiththeVIIIthnerverootsandtoalesserdegreewithVIIthlateral-lineroots.TheprimaryobjectiveoftheexperimentswastorecordfromalargeseriesofanimalsthenumberofcasesinwhichMCfailedtodifferentiateintheabsenceofVIIIthrootfibers.Inaddition,allembryoswereseparated(stages3,5,9)intovariousgroupsandmaintainedcontinuouslyatdifferentconstanttemperatures(5°,8°,10°,14°,18°C)untiloperation.ThevarioustemperaturegroupswerethencomparedamongthemselvesforanyconstantorsignificantdifferenceswithregardtothesuppressionofMContheoperatedside.Animalswereexaminedatstage46.TheVIIIthrootfiberswerecompletelyabsentineverycaseontheoperatedside.AlthoughtheVIIthlateral-linegangliawerepresentinallanimals,rootfibersfailedtodevelopin173cases.ThisaffordedanopportunitytostudytheinfluenceofVIIthlateral-linerootsuponthedifferentiationofMC,aswellastheinfluenceofVIIIthroots.Mauthner'scellwasabsentin119cases(27.8%).In55ofthesecasesonlyVIIIthrootfiberswereabsent;in64casesbothVIIIthandVIIthrootsweremissing.TheimportanceofVIIIthrootfibersininfluencingthedifferentiationofMC,therefore,isobvioussincein46%ofthosecasesinwhichMCfailedtodevelopabsenceoftheVIIIthrootwastheonlydeviationfromnormal.ThepresenceorabsenceofMCcorrelatedwiththepresenceorabsenceofVIIthlateral-linerootsgivesarelativelyhighChi-squarevalueof11.461.ThetemperatureseriesdataareinconclusiveindemonstratingacriticaloroptimalthermaleffectuponthesequentialstepsaffectingthedifferentiationofMC.Ifthetimeinearlydevelopmentwhentemperaturedifferentialswereappliedisignored,therearenoconsistentorsignificantdifferencesamongthetemperaturegroupswithregardtothesuppressionofMCintheabsenceoftheVIIth–VIIIthrootcomplex.Ontheotherhand,ifonlythoseanimalsareconsideredthatwereseparatedatstage9(themajorityoftheanimals),thenthereisalowdegreeofcorrelation(significanceslightlyabovethe1%level)betweengreatersuppressionofMCinthe8°groupsasopposedtolessersuppressioninthe14°groups.Theseresultsontemperatureinfluenceareinneedoffurtherexperimentationandanalysis.

[学科分类] 生物科学（综合）