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 green fluorescent protein (GFP) fused with BDNF. First, several biological studies confirmed that this fusion protein (BDNF-GFP) mimics the biological functions and the release kinetics of unfused (native) BDNF. Second, when BDNF-GFP was expressed in cultured hippocampal neurons, we observed that this protein formed striking clusters in the neurites of mature neurons and colocalized with the PSD-95 immunoreactivity. Such a clustered BDNF-GFP rapidly disappeared in response to depolarization with KCl, as revealed by confocal 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.