Biological characterization and optical imaging of brain-derived neurotrophic factor-green fluorescent protein suggest an activity-dependent local release of brain-derived neurotrophic factor in neurites of cultured hippocampal neurons

To visualize the release dynamics of the brain-derived neurotrophic factor (BDNF) involved in neural plasticity, we constructed a plasmid encoding gre en fluorescent protein (GFP) fused with BDNF. First, several biological stu dies confirmed that this fusion protein (BDNF-GFP) mimics the biological fu nctions and the release kinetics of unfused (native) BDNF. Second, when BDN F-GFP was expressed in cultured hippocampal neurons, we observed that this protein formed striking clusters in the neurites of mature neurons and colo calized with the PSD-95 immunoreactivity. Such a clustered BDNF-GFP rapidly disappeared in response to depolarization with KCl, as revealed by confoca l microscopic studies. These data suggest that BDNF is locally and rapidly released at synaptic sites in an activity-dependent manner. Optical studies using BDNF-GFP may provide important evidence regarding the participation of BDNF in synaptic plasticity. (C) 2001 Wiley-Liss, Inc.