Figure 11. Synaptopathy of individual type I_a endbulb of Held synapses during ARHL.

(A) Representative morphology of individual type I_a endbulb of Held synapses in young mice. Panels from left to right: filled neurons (magenta) with reconstructed individual type I_a endbulbs, type I_a endbulbs alone, type I_a endbulbs (semi-transparent) with enclosed VGluT1-labled puncta (yellow), and VGluT1-labeled puncta alone. Top panels: example bushy neuron with only one type I_a endbulb of Held synapse. Bottom panels: example neuron with two type I_a endbulb of Held synapses, which are shown in red and blue respectively.

(B) Representative morphology of individual type I_a endbulb of Held synapses in middle-aged mice.

(C) Representative morphology of individual type I_a endbulb of Held synapses in old mice. Scales in A-C: 5 μm.

(D-F) Comparisons of individual type I_a endbulb volume (D), enclosed VGluT1-puncta volume (E), and VGluT1/endbulb volume ratio (F) among three age groups. Dunn’s multiple comparison test: NS, p > 0.05; ****p < 0.0001.