Seena Mathew - Published Work
BDNF causes action potential-independent vesicular release from presynaptic terminals labeled with FM1-43: multiphoton excitation microscopy in area CA1 of hippocampal slices
by M. D. AMARAL, S. S. MATHEW, G.
RUMBAUGH, L. POZZO-MILLER;
BDNF is well known as a survival signal in the developing brain, as well as a regulator of adult synaptic transmission and plasticity. A potential mechanism for BDNF actions at synapses is the modulation of quantal transmitter release. Previously, we have shown that a single local application of recombinant human mature BDNF to CA1 stratum radiatum of hippocampal slice cultures induced a significant increase in mEPSCs frequency within 30sec of its ejection, an effect that outlasted the BDNF stimulus (Amaral & Pozzo-Miller, SfN Abstracts, 2004). mEPSC amplitude was not changed during these barrages of mEPSCs, indicating a presynaptic site of BDNF action. In order to identify the underlying presynaptic mechanism responsible for this increase in mEPSC frequency, we labeled the total recycling vesicle pool with the styryl dye, FM1-43 using a high K+ solution. BDNF was locally applied to CA1 stratum radiatum using a picospritzer (~10-15psi, 25-30sec) in the presence of 500nM TTX and the resulting changes in FM1-43 fluorescence puncta were monitored by multiphoton excitation microscopy (840nm excitation). We found that acute BDNF application resulted in significant destaining of FM1-43 puncta following a mono-exponential time course, indicating that it originated from full vesicular fusion events that allow FM1-43 to escape the vesicle lumen. Intriguingly, FM1-43 destaining did not occur until 140sec following a single BDNF application, a time delay during which the frequency of mEPSCs evoked by BDNF is at its peak (20-40Hz). It is tempting to speculate that this early phase of heightened mEPSC frequency without detectable FM1-43 destaining involves rapid vesicle reuse, which is too fast to allow FM1-43 release, whereas the delayed mono-exponential FM1-43 destaining reflects slower full-fusion events. We conclude that acute local application of BDNF to CA1 stratum radiatum in hippocampal slice cultures rapidly enhances action potential-independent vesicular release, which represents the underlying mechanism of the presynaptic actions of BDNF.
Program No. 443.8. 2007. San Diego, CA: Society for Neuroscience, 2007.
2007 Copyright by the Society for Neuroscience all rights reserved.