title: The influence of activity on axon pathfinding in the optic tectum.
abstract: The relative importance of neural activity versus activity-independent cues in shaping the initial wiring of the brain is still largely an open question. While activity is clearly critical for circuit rearrangements after initial connections have been made, whether it also plays a role in initial axon pathfinding remains to be determined. Here, we investigated this question using the guidance of zebrafish retinal ganglion cell axons to their targets in the tectum as a model. Recent results have implicated biased branching as a key feature of pathfinding in the zebrafish tectum. Using tetrodotoxin to silence neural activity globally, we found a decrease in the area covered by axon branches during pathfinding. After reaching the target, there were dynamic differences in axon length, area and the number of branches between conditions. However, other aspects of pathfinding were unaffected by silencing, including the ratio of branches directed toward the target, length, and number of branches, as well as turning angle, velocity, and number of growth cones per axon. These results challenge the hypothesis that neural connections develop in sequential stages of molecularly guided pathfinding and activity-based refinement. Despite a maintenance of overall guidance, axon pathfinding dynamics can nevertheless be altered by activity loss.
authors.affiliation: Queensland Brain Institute, The University of Queensland, Brisbane, Australia.
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Kita
authors.affiliation: School of Biomedical Sciences, The University of Queensland, Brisbane, Australia.
authors.forename: Ethan K
authors.initials: EK
authors.lastname: Scott
authors.affiliation: Queensland Brain Institute, The University of Queensland, Brisbane, Australia.|School of Mathematics and Physics, The University of Queensland, Brisbane, Australia.
authors.forename: Geoffrey J
authors.initials: GJ
authors.lastname: Goodhill
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D001369:Axons / Q000187:drug effects / Q000502:physiology*; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism; D019521:Body Patterning / Q000187:drug effects / Q000502:physiology*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D004625:Embryo, Nonmammalian; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D007814:Larva; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D026941:Sodium Channel Blockers / Q000494:pharmacology; D013477:Superior Colliculi / Q000166:cytology / Q000196:embryology / Q000254:growth & development; D013779:Tetrodotoxin / Q000494:pharmacology; D050818:Transcription Factor Brn-3 / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014795:Visual Pathways / Q000187:drug effects / Q000196:embryology* / Q000254:growth & development*; D015027:Zebrafish; D029961:Zebrafish Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D004268:DNA-Binding Proteins; D049452:Green Fluorescent Proteins; D026941:Sodium Channel Blockers; D013779:Tetrodotoxin; D050818:Transcription Factor Brn-3; D014157:Transcription Factors; D029961:Zebrafish Proteins; C542436:Gal4 protein, zebrafish
keywords: axon pathfinding; neural development; retinal ganglion cell; tectum; tetrodotoxin; time-lapse; topographic maps; zebrafish