Embryogenesis of peripheral nerve pathways in grasshopper legs: I. The initial nerve pathway to the CNS☆

摘要

Thefoundingofthefirstnervepathofthegrasshoppermetathoraciclegwasexaminedatthelevelofidentifiedneurons,usingintracellulardyefills,immunohistochemistry,Nomarskioptics,andscanningandtransmissionelectronmicroscopy.Theembryonicnerveisestablishedbytheaxonaltrajectoryofapairofafferentpioneerneurons,thetibial1(Ti1)cells.Followingaperiodofprofusefilopodialsprouting,theTi1axonalgrowthcones,possessing75-to100-??m-longfilopodia,navigateastereotypedpathacrossthelimbbudepitheliumtothebaseoftheappendageandintotheCNS.TheTi1axonsgrowfromcelltocellalongachainofpreaxonogenesisneuronsspacedatintervalsalongthepathway,formingdye-passingjunctionswiththem.ThecontactedneuronssubsequentlyundergoaxonogenesisandfollowthepioneeraxonsintotheCNS.Laterarisingneuronsprojecttheiraxonsontothecellbodiesofthechain,therebyestablishingtheprincipalbranchpointsofthenerve.Amongthelaterarisingafferentsarethesensoryneuronsofthefemoralchordotonalandsubgenualorgans.Themorphologyoftheadultnerveappearstobedeterminedbythestereotypedpositioningofneuronsinthedifferentiatinglimbbudandbytheresultantaxonaltrajectoriesestablishedduringthefirst10%ofperipheralneurogenesis.