Development of neurons in the abdominal ganglion of Aplysia californica: I. Axosomatic synaptic contacts☆

摘要

ThedevelopmentofmariculturetechniquesfortheraisingofAplysiacalifornicainthelaboratoryfromfertilizedeggtoreproductivelymatureadultpermitsthestudyofthedevelopmentalprogramwherebyindividualidentifiedneuronsintheabdominalganglionacquiretheirspecificadultproperties.Inthispaper,wedescribeoneoftheearlystepsofthisdevelopmentalprogram:theoutgrowthofaxonalprocessesbyneuronsoftheabdominalganglion.Axonaloutgrowthiscorrelatedwithandmaybetriggeredbythetransientappearanceofmorphologicallyidentifiableaxosomaticcontactsbetweentheasyetundifferentiatedcellbodyofspecificneuronsandanaxonterminalfromanincomingnervefiberfromthepleuroabdominalconnective.Theevidencethattransientaxosomaticcontactsmaysignalneuronaldifferentiationisthefollowing:(1)Axosomaticcontactshavenotbeenobservedintheabdominalganglionofadultanimals,whereastheyarecommonlyobservedduringtheearlystagesofdevelopment.(2)Cellsthatreceiveaxosomaticcontactsareundifferentiatedmorphologicallyanddonotasyethaveaxons.Bycontrast,cellswithaxonsdonothavesomacontacts.(3)Individualcellsthatcanbeidentifiedfromanimaltoanimalinthesameandsucceedingdevelopmentalstagesreceiveaxosomaticcontactsonsimilartopographicpostionsofthecellbodyatonepointindevelopment.Axonoutgrowththenoccursatthesiteofcontact.Laterindevelopment,withfurtheraxonextension,thesecellsnolongerhavesynapticcontactsonthecellbodyoraxon.