Individual Brain-derived Neurotrophic Factor Research Articles

The timecourse of induction of brain-derived neurotrophic factor mRNA and protein in the rat hippocampus following voluntary exercise

In this study we examined the timecourse of induction of brain-derived neurotrophic factor (BDNF) mRNA and protein after 1, 3, 5, 7, 14 and 28 days of exercise in the rat. To measure the expression of mRNA for individual BDNF exons we utilized a semi-quantitative RT-PCR technique, while BDNF protein was assessed using commercial ELISA kits. We demonstrated that the distance run by animals increased significantly ( P<0.05) after 4 weeks. BDNF protein was significantly ( P<0.05) increased after 4 weeks of exercise, while the mRNA for individual BDNF exons increased significantly ( P<0.05) over the timecourse (exon I after 1 and 28 days and exons II and V after 28 days). The Morris water maze was then utilized to demonstrate that 3 weeks of prior exercise enhanced the rate of learning on this task. Exercise, therefore, was shown to modulate BDNF induction in a time-dependent manner, and this may translate to improvements in neurotrophin-mediated tasks within the CNS.

Differential expression of brain-derived neurotrophic factor transcripts after pilocarpine-induced seizure-like activity is related to mode of Ca 2+ entry

Activity-dependent brain-derived neurotrophic factor (BDNF) expression is Ca 2+-dependent, yet little is known about the Ca 2+ channel contributions that might direct selective expression of the multiple BDNF transcripts. Here, effects of pilocarpine-induced seizure activity on total BDNF expression and on the individual sensitivity of BDNF transcripts to glutamate receptor and Ca 2+ channel blockers were evaluated using hippocampal slice cultures and in situ hybridization of transcript-specific cRNA probes directed against mRNAs for the four 5′ exons (I–IV) of the BDNF gene. mRNAs for nerve growth factor (NGF) and tyrosine kinase B (trkB) also were studied. Pilocarpine (5 mM) induced a dose- and time-dependent increase in total BDNF (exon V) mRNA expression in the dentate granule cells and CA3–CA1 pyramidal cells with maximal effects at 6 and 24 h, respectively. Increases were blocked by co-treatment with the α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid/kainate 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX: 25 μM) and the N-methyl- d-aspartic acid receptor antagonist 2-amino-5-phosphonovaleric acid (APV; 25 μM), whereas the L-type voltage sensitive Ca 2+ channel blocker nifedipine (20 μM) was without detectable effect. Maximal NGF and trkB mRNA expression was induced by pilocarpine at 4 and 12 h, respectively. For the individual BDNF transcripts, APV blocked pilocarpine-induced increases in transcript II, whereas nifedipine blocked increases in transcripts I and III. Transcript IV levels were not altered by treatment. These results indicate that transcript II makes the greatest contribution to pilocarpine effects on total BDNF mRNA content in this model and provides evidence for regional and Ca 2+ channel-specific differences in activity-dependent regulation of the different BDNF transcripts in hippocampus.

Changes in protein conformation and dynamics upon complex formation of brain-derived neurotrophic factor and its receptor: Investigation by isotope-edited Fourier transform IR spectroscopy

The interactions of brain-derived neurotrophic factor (BDNF) with the extracellular domain of its receptor (trkB) are investigated by employing isotope-edited Fourier transform IR (FTIR) spectroscopy. The protein secondary structures of individual BDNF and trkB in solutions are compared with those in their complex. The temperature dependence of the secondary structures of BDNF, trkB, and their complex is also investigated. Consistent with the crystal structure, we observe by FTIR spectroscopy that BDNF in solution contains predominantly β strands (∼53%) and relatively low contents of other secondary structures including β turns (∼16%), disordered structures (∼12%), and loops (∼18%) and is deficient in α helix. We also observe that trkB in solution contains mostly β strands (52%) and little α helix. Conformational changes in both BDNF and trkB are observed upon complex formation. Specifically, upon binding of BDNF, the conformational changes in trkB appear to involve mostly β turns and disordered structures while the majority of the β-strand conformation remains unchanged. The IR data indicate that some of the disordered structures in the loop regions are likely converted to β strands upon complex formation. The FTIR spectral data of BDNF, trkB, and their complex indicate that more amide NH groups of trkB undergo H–D exchange within the complex than those of the ligand-free receptor and that the thermal stability of trkB is decreased slightly upon binding of BDNF. The FT-Raman spectra of BDNF, trkB, and their complex show that the six intramolecular disulfide bonds of trkB undergo significant conformational changes upon binding of BDNF as a result of changes in the tertiary structure of trkB. Taken together, the FTIR and Raman data are consistent with the loosening of the tertiary structure of trkB upon binding of BDNF, which leads to more solvent exposure of the amide NH group and decreased thermal stability of trkB. This finding reveals an intriguing structural property of the neurotrophin ligand–receptor complex that is in contrast to other ligand–receptor complexes such as a cytokine–receptor complex that usually shows protection of the amide NH group and increased thermal stability upon complex formation. © 2002 John Wiley & Sons, Inc. Biopolymers (Biospectroscopy) 67: 10–19, 2002; DOI 10.1002/bip.10038