Studies on the mechanics of development of the visual pathways in the chick embryo☆

[摘要] Silver-stainedwholemountsofthetectalsurfacewereusedtostudythedevelopingretinotectalfiberpathwayinthechickembryo.Thegrowingfrontofopticfibersappearedmoredisorderedthanfiberbundlestotherear.Thefiberpatternasawholeappearedmoreorderlywithage.Somefibersprojectedsparselyaheadofthegrowingfrontinapatternsuggestingtheexistenceofpreneuralguidancechannels.Fiberbranchingwasrarelyseen.Anorthogonalgridworkoftwolayersoffibers,runningroughlyanteroposteriorlyanddorsoventrally,wasfoundonthedevelopingtectalsurfaceafterremovalofbothopticvesicles.Inunoperatedspecimens,fibersintheopticfiberlayerfollowedthesegridlines.Retinalquadrantsfromembryos4–5daysoldweretransplantedtotheoptictectaofembryos6–7daysold.Thegraftfiberssubsequentlydidnotshowspecificorientationtowardtheirappropriatetectalquadrant.Rather,thefibersfollowedthesamestraightcoursestakenbycarbonparticlesimplantedincomparablepositionsincontrols.Aftertheproductionofquadrantalretinallesionsin4–5day-oldembryos,noevidencewasfoundforspecifictectalinnervationdefectsat12–13days.Lesions,irrespectiveofretinalquadrant,resultedinarelativelackofinnervationintheposterodorsalaspectofthe12–13day-oldtectum.Thiswasprobablyduetoadelayintheadvancementofthegrowingfrontoffibersacrossthetectalsurface.Theresultsweakenprevioussupportforspecificityintheguidanceofdevelopingopticaxons.

[学科分类] 生物科学（综合）