title: Laminar specificity of local circuits in barrel cortex of ephrin-A5 knockout mice.
abstract: Cortical circuits are characterized by layer-specific axonal arbors. Molecular laminar cues are believed to direct the development of this specificity. We have tested the hypothesis that ephrin-A5 is responsible for preventing layer 2/3 pyramidal cell axons from branching within layer 4 (Castellani et al., 1998) by assessing the laminar specificity of axonal arbors in ephrin-A5 knockout mice. We find that in barrel cortex of knockout mice, layer 2/3 pyramidal neurons form axonal arbors specifically in layers 2/3 and 5, avoiding layer 4. This pattern of arborization is indistinguishable from that of wild-type littermates. Furthermore, we find that in wild-type mice, laminar patterns of ephrin-A5 expression differ between cortical areas despite the similarity of layer-specific local cortical circuits across areas. Most notably, ephrin-A5 is not expressed preferentially in layer 4 of wild-type mouse barrel cortex. We conclude that ephrin-A5 is not responsible for preventing the development of layer 2/3 pyramidal cell axonal arbors in layer 4 of mouse barrel cortex. These observations also suggest that if ephrin-A5 plays a role in the emergence of layer-specific circuits, that role must differ between cortical areas.
authors.affiliation: Systems Neurobiology Laboratories, The Salk Institute for Biological Studies, La Jolla, California 92037, USA.
authors.forename: N H
authors.initials: NH
authors.lastname: Yabuta
authors.forename: A K
authors.initials: AK
authors.lastname: Butler
authors.forename: E M
authors.initials: EM
authors.lastname: Callaway
mesh_terms: D000818:Animals; D001369:Axons / Q000378:metabolism / Q000648:ultrastructure; D003712:Dendrites / Q000378:metabolism / Q000648:ultrastructure; D036386:Ephrin-A5; D066298:In Vitro Techniques; D008239:Lysine / Q000031:analogs & derivatives*; D008565:Membrane Proteins / Q000096:biosynthesis / Q000172:deficiency* / Q000235:genetics; D051379:Mice; D018345:Mice, Knockout; D009415:Nerve Net / Q000166:cytology* / Q000254:growth & development / Q000378:metabolism; D018408:Patch-Clamp Techniques; D017966:Pyramidal Cells / Q000166:cytology / Q000378:metabolism; D013003:Somatosensory Cortex / Q000166:cytology* / Q000254:growth & development / Q000378:metabolism
chemical_list: D036386:Ephrin-A5; D008565:Membrane Proteins; C013411:biocytin; D008239:Lysine