Anatomical changes at light and ultrastructure levels. (A and B) Endbulbs immunolabeled for VGLUT-1 in control (A) and noise-reared (B) animals. BC somata are surrounded by multiple VGLUT-1–positive puncta. (Scale bar: A and B, 20 µm.) (C) Puncta area for endbulbs from control and noise-reared mice. Horizontal lines mark average areas of puncta around individual BCs, and bars are overall averages across all cells (10 control, 15 noise-reared). The average area of puncta around noise-reared BCs is significantly greater than around control BCs (P < 0.05). (D and E) Representative profiles of endbulbs from control (D) and noise-reared (E) animals. Each profile has numerous synaptic vesicles, curved and asymmetric postsynaptic densities (asterisks). (Scale bar: D and E, 1 µm.) (F–H) Endbulbs in noise-reared mice had significantly more postsynaptic densities per profile (P < 0.05, Fisher exact test; F), larger profile perimeter and cross-sectional area (P < 0.001; G) and larger form factors (P < 0.001; H).