title: Crucial role of TrkB ligands in the survival and phenotypic differentiation of developing locus coeruleus noradrenergic neurons.
abstract: The role of glial cell-line derived neurotrophic factor (GDNF) and neurotrophins in the development of locus coeruleus noradrenergic neurons was evaluated. We found that two neurotrophic factors previously reported to prevent the degeneration of lesioned adult central noradrenergic neurons, GDNF and neurotrophin 3 (NT3), do not play significant roles in the prenatal development of locus coeruleus noradrenergic neurons, as demonstrated by: (1) the lack of alterations in double Gdnf/Nt3 null mutant mice; and (2) the lack of survival-promoting effects of GDNF and/or NT3 in rat E13.5 primary cultures. In contrast, null mutant mice for TrkB, the tyrosine kinase receptor for brain-derived neurotrophic factor and neurotrophin 4, displayed a clear loss of locus coeruleus noradrenergic neurons. In accordance with this, treatment of rat E13.5 primary cultures with TrkB ligands prevented the early loss of noradrenergic neurons and maintained their survival for up to 6 days in vitro. Moreover, an additional 5-10-fold increase in the number of tyrosine hydroxylase positive noradrenergic neurons was detected after 12 hours in culture. This second effect of TrkB ligands involved neither proliferation nor survival, because the number of BrdU- or TUNEL-positive noradrenergic neurons did not change and the effect was elicited by delayed administration of either factor. Because TrkB ligands increased the number of tyrosine hydroxylase-positive cells expressing Phox2a, a paired homeodomain protein required for the development of locus coeruleus noradrenergic neurons, but did not affect the number of Phox2a-positive tyrosine hydroxylase-negative cells, our results suggest that the second effect of TrkB ligands may involve promoting or inducing a noradrenergic phenotype. In summary, our findings suggest that, unlike NT3 and GDNF, TrkB ligands are required and sufficient to promote the development of central noradrenergic neurons.
authors.affiliation: Department of Medical Biochemistry and Biophysics, Laboratory of Molecular Neurobiology, Karolinska Institutet, Stockholm S-171 77, Sweden.
authors.forename: Pontus C
authors.initials: PC
authors.lastname: Holm
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: Rodríguez
authors.forename: Adelheid
authors.initials: A
authors.lastname: Kresse
authors.forename: Josep M
authors.initials: JM
authors.lastname: Canals
authors.forename: Inmaculada
authors.initials: I
authors.lastname: Silos-Santiago
authors.forename: Ernest
authors.initials: E
authors.lastname: Arenas
mesh_terms: D000818:Animals; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D051100:Glial Cell Line-Derived Neurotrophic Factor; D051097:Glial Cell Line-Derived Neurotrophic Factor Receptors; D008024:Ligands; D008125:Locus Coeruleus / Q000196:embryology*; D008562:Membrane Glycoproteins / Q000378:metabolism*; D051379:Mice; D009154:Mutation; D009414:Nerve Growth Factors / Q000235:genetics / Q000378:metabolism; D009474:Neurons / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051096:Proto-Oncogene Proteins c-ret; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism; D020813:Receptor, trkB / Q000378:metabolism; D020812:Receptor, trkC / Q000378:metabolism
chemical_list: C495040:Gdnf protein, mouse; D051100:Glial Cell Line-Derived Neurotrophic Factor; D051097:Glial Cell Line-Derived Neurotrophic Factor Receptors; D008024:Ligands; D008562:Membrane Glycoproteins; D009414:Nerve Growth Factors; D011518:Proto-Oncogene Proteins; C064371:Ntrk2 protein, mouse; D011505:Protein-Tyrosine Kinases; D051096:Proto-Oncogene Proteins c-ret; D020794:Receptor Protein-Tyrosine Kinases; D020813:Receptor, trkB; D020812:Receptor, trkC