title: Comparison of neurotrophin and repellent sensitivities of early embryonic geniculate and trigeminal axons.
abstract: Geniculate (gustatory) and trigeminal (somatosensory) afferents take different routes to the tongue during rat embryonic development. To learn more about the mechanisms controlling neurite outgrowth and axon guidance, we are studying the roles of diffusible factors. We previously profiled the in vitro sensitivity of trigeminal axons to neurotrophins and target-derived diffusible factors and now report on these properties for geniculate axons. GDNF, BDNF, and NT-4, but not NT-3 or NGF, stimulate geniculate axon outgrowth during the ages investigated, embryonic days 12-14. Sensitivity to effective neurotrophins is developmentally regulated and different from that of the trigeminal ganglion. In vitro coculture studies revealed that geniculate axons were repelled by branchial arch explants that were previously shown to be repellent to trigeminal axons (Rochlin and Farbman [1998] J Neurosci 18:6840-6852). In addition, some branchial arch explants and untransfected COS7 cells repelled geniculate but not trigeminal axons. Sema3A, a ligand for neuropilin-1, is effective in repelling geniculate and trigeminal axons, and antineuropilin-1, but not antineuropilin-2, completely blocks the repulsion by arch explants that repel axon outgrowth from both ganglia. Sema3A mRNA is concentrated in branchial arch epithelium at the appropriate time to mediate the repulsion. In Sema3A knockout mice, geniculate and trigeminal afferents explore medial regions of the immature tongue and surrounding territories not explored in heterozygotes, supporting our previous hypothesis that Sema3A-based repulsion mediates the early restriction of sensory afferents away from midline structures.
authors.affiliation: Neurobiology and Physiology, Northwestern University, Chicago, Illinois 60208, USA. wrochli@luc.edu
authors.forename: M W
authors.initials: MW
authors.lastname: Rochlin
authors.forename: R
authors.initials: R
authors.lastname: O'Connor
authors.forename: R J
authors.initials: RJ
authors.lastname: Giger
authors.forename: J
authors.initials: J
authors.lastname: Verhaagen
authors.forename: A I
authors.initials: AI
authors.lastname: Farbman
mesh_terms: D000818:Animals; D001369:Axons / Q000187:drug effects* / Q000502:physiology; D019208:Brain-Derived Neurotrophic Factor / Q000494:pharmacology; D019556:COS Cells; D002478:Cells, Cultured; D005830:Geniculate Ganglion / Q000187:drug effects* / Q000196:embryology / Q000502:physiology; D051100:Glial Cell Line-Derived Neurotrophic Factor; D051379:Mice; D018345:Mice, Knockout; D009414:Nerve Growth Factors / Q000378:metabolism / Q000494:pharmacology*; D009419:Nerve Tissue Proteins / Q000494:pharmacology; D020933:Neurotrophin 3 / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D014059:Tongue / Q000196:embryology / Q000294:innervation*; D012668:Trigeminal Ganglion / Q000187:drug effects* / Q000196:embryology / Q000502:physiology
chemical_list: D019208:Brain-Derived Neurotrophic Factor; C495040:Gdnf protein, mouse; C495041:Gdnf protein, rat; D051100:Glial Cell Line-Derived Neurotrophic Factor; D009414:Nerve Growth Factors; D009419:Nerve Tissue Proteins; D020933:Neurotrophin 3; C073922:neurotrophin 4