Emergence and refinement of clustered horizontal connections in cat striate cortex

摘要: Pyramidal cells in layer 2/3 of adult cat striate cortex have long, intrinsic horizontal axon collaterals within both and 5. These form periodic "clusters" finer branches that link columns similar orientation selectivity. We investigated the sequence events possible mechanisms underlying development these clustered connections using a combination neuronal tracers intracellular staining. Small injections fluorescent latex microspheres made during first postnatal week (at P4-6), when examined tangential sections, produced an even, unclustered distribution retrogradely labeled up to 2 mm from injection site. At P8, retrograde labeling extended over larger area clustering was discernible, primarily among most distant cells. P6 layers 5, indicating transition occurred simultaneously for superficial deep laminae. By end second (P12-15), were far more beyond extent label; density high throughout region, but much higher clusters. The periodicity nascent clusters adult. Despite obvious clustering, pattern label observed following at 2-3 weeks (P12-21) differed markedly adult, regions between contained many Over next 3 weeks, refined, so by sixth (P36-38), very few overall indistinguishable adults. differences postmigratory ages neurons laminae, populations all ages. Experiments which elapsed time microsphere animals killed demonstrated neither initial formation crude nor their refinement due cell death. Instead, cluster resulted specific process elimination. When red P15 followed green exactly same location on P29, earlier as expected. Virtually double-labeled later densest early injection.(ABSTRACT TRUNCATED AT 400 WORDS)