Figure 3.

Ultrastructural analysis reveals an increase in PSD length in Bsn^ΔEx4/5 endbulbs.

A, B  Example electron micrographs of Bsn^wt (A) and Bsn^ΔEx4/5 (B) bushy cells (scale bars, 2 μm) and endbulb of Held synapse AZs (scale bars, 100 nm). Structures highlighted in cyan represent asymmetric, excitatory presynaptic terminals onto the postsynaptic soma.

C  The length of the postsynaptic density (PSD) was significantly increased in Bsn^ΔEx4/5 endbulb synapses.

D  When normalized to PSD length, vesicle counts in the first bin were significantly decreased, but the number of vesicles in direct contact with the presynaptic plasma membrane remained unchanged.