Abstract
Synaptic plasticity is considered to underly information processing and memory formation in the brain and stabilization of neurotransmission during plasticity likely includes reorganization of active zones (AZs).Here, we used localization microscopy and hierarchical density-based spatial clustering to probe AZ architecture at the Drosophila melanogaster neuromuscular junction. We observed distinct arrangements of the scaffold protein Bruchpilot (Brp) at AZs of high release probability type Is and low release probability type Ib boutons. Most remarkably, Brp proteins at type Is AZs were arranged more compact than at type Ib AZs. To ascertain whether adaptations of the AZ scaffold also occur in response to short-term demands, we used philanthotoxin (PhTx) to induce acute homeostatic plasticity. PhTx decreased AZ size, the distance between Brp subclusters and the AZ center, leading to compaction of the Brp scaffold. These changes only occurred at type Ib but not type Is AZs which, already compact, did not undergo structural rearrangement. In summary, our data describe a molecular compaction of the AZ scaffold reflecting the functional demands at high release probability synapses and during an acute homeostasic challenge.
