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Neurotrophins Stimulate Chemotaxis of Embryonic Cortical Neurons
Author(s) -
Behar T. N.,
DugichDjordjevic M. M.,
Li YX.,
Ma W.,
Somogyi R.,
Wen X.,
Brown E.,
Scott C.,
McKay R. D. G.,
Barker J. L.
Publication year - 1997
Publication title -
european journal of neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.346
H-Index - 206
eISSN - 1460-9568
pISSN - 0953-816X
DOI - 10.1111/j.1460-9568.1997.tb01685.x
Subject(s) - tropomyosin receptor kinase b , chemotaxis assay , microbiology and biotechnology , chemotaxis , neurotrophin , biology , bapta , tropomyosin receptor kinase a , trk receptor , brain derived neurotrophic factor , neurotrophic factors , receptor , chemistry , neuroscience , biochemistry , intracellular
During mammalian cortical development, neuronal precursors proliferate within ventricular regions then migrate to their target destinations in the cortical plate, where they organize into layers. In the rat, most cortical neuronal migration occurs during the final week of gestation (Bayer et al ., 1991; Jacobson, 1991). At this time (E15–E21), reverse transcriptase‐polymerase chain reaction demonstrated that cortical homogenates contain mRNA encoding brain derived neurotrophic factor (BDNF) and the catalytic form of its high‐affinity receptor, TrkB. lmmunocytochemistry and in situ hybridization of sections revealed that the catalytic TrkB receptors predominantly localize to regions containing migratory cells. Many TrkB+ cells exhibited the classic morphology of migrating neurons, suggesting that TrkB ligands play a role in cortical neuronal migration. We analysed whether TrkB ligands influence the motility of embryonic cortical cells (from E15–E21) using a quantitative in vitro chemotaxis assay. High‐affinity TrkB ligands (BDNF and NT4/5) stimulated chemotaxis (directed migration) of embryonic neurons at concentrations ranging from 1 to 100 ng/ml. NT‐3, a low‐affinity TrkB ligand, only stimulated significant migration at high concentrations (±100 ng/ml). Peak migration to BDNF was observed at gestational day 18 (E18). BDNF‐induced chemotaxis was blocked by either tyrosine kinase inhibitor, K252a, or the Ca 2+ ‐chelator, BAPTA‐AM, suggesting that BDNF‐induces motility via autophosphorylation of TrkB receptor proteins and involves Ca 2+ ‐dependent mechanisms. BDNF‐stimulation of increased cytosolic Ca 2+ was confirmed with optical recordings of E18 cortical cells loaded with Ca 2+ indicator dye. Thus, signal transduction through the TrkB receptor complex directs neuronal migration, suggesting that, in vivo , BDNF exerts chemotropic effects that are critical to morphogenesis of the cortex.