Fig. 4. Anti-BDNF rapidly influences presynaptic site and axon branch stability.
(A) Diagrammatic representation of GFP-synaptobrevin cluster dynamics and
arbor growth. The number of GFP-synaptobrevin clusters stabilized and
eliminated, and the number of new GFP-synaptobrevin clusters added between
observation intervals was calculated and normalized for each time interval to
obtain a dynamic measure of synapse addition and stabilization over time. As
new GFP-synaptobrevin clusters are added, the absolute number of clusters that
are stabilized increases, but as a proportion it remains relatively constant.
The hypothetical axon depicted here exhibits rates of synapse stabilization
that are slightly higher than those observed for RGC axon arbors in
vehicle-treated tadpoles (control). (B) Detailed analysis of the number and
distribution of GFP-synaptobrevin clusters per axon branch, and of the
lifetimes of individual GFP-synaptobrevin clusters for every observation
period reveal the effects of neutralizing endogenous BDNF on synapse
stabilization. Anti-BDNF significantly reduced the stability of
GFP-synaptobrevin clusters by 2 hours (0-2 hours), an effect that was
maintained through every observation period. (C) Analysis of the number of
axon branches that are retained or eliminated from one observation interval to
the next provides a measure of the effects of anti-BDNF on axon branch
stability. Axon branches are significantly destabilized and eliminated 0-2
hours after treatment and this effect is maintained for the first 6 hours
following treatment. On average, 60.2±2.6% of branches are stable every
2 hours in anti-BDNF treated arbors versus 73.3±1.6% in controls.
*P
0.05; **P0.005.