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Axons of callosal neurons bifurcate transiently at the white matter before consolidating an interhemispheric projection

Authors

  • Patricia P. Garcez,

    1. Departamento de Anatomia, Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro, 21941–590, Rio de Janeiro, Brazil
    2. Institut für Allgemeine Zoologie und Tierphysiologie, Friedrich Schiller Universität, Jena, Germany
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  • Narjara P. Henrique,

    1. Departamento de Anatomia, Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro, 21941–590, Rio de Janeiro, Brazil
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  • Danilo A. Furtado,

    1. Departamento de Anatomia, Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro, 21941–590, Rio de Janeiro, Brazil
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  • Jürgen Bolz,

    1. Institut für Allgemeine Zoologie und Tierphysiologie, Friedrich Schiller Universität, Jena, Germany
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  • Roberto Lent,

    1. Departamento de Anatomia, Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro, 21941–590, Rio de Janeiro, Brazil
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  • Daniela Uziel

    1. Departamento de Anatomia, Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro, 21941–590, Rio de Janeiro, Brazil
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Dr Daniela Uziel, as above.
E-mail: daniuzi@anato.ufrj.br

Abstract

The main alternative output routes of adult cortical axons are the internal capsule and the corpus callosum. How do callosal axons choose their trajectories? We hypothesized that bifurcation followed by elimination of one branch is a developmental strategy for accomplishing this aim. Using embryonic and postnatal mice, we labelled cortical projecting neurons and quantified their axonal bifurcations in correlation with the mediolateral position of their somata. Bifurcating axons were numerous in the younger brains but declined during further development. Most bifurcating axons pertained to neurons located in the dorsolateral cortex. Moreover, callosal neurons bifurcate more often than subcortically projecting cells. We then quantified bifurcations formed by dissociated green fluorescent cells plated onto cortical slices. Cells grown over dorsolateral cortex bifurcated more often than those grown over medial cortex, irrespective of their positional origin in the donor. Removal of intermediate targets from the slices prevented bifurcation. We concluded that transient bifurcation and elimination of the lateral branch is a strategy employed by developing callosal axons in search of their targets. As cell body position and intermediate targets determine axon behaviour, we suggest that bifurcations are regulated by cues expressed in the environment.

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