Changes of ribbon synapses number of cochlear hair cells in C57BL/6J mice with age(Δ)

To investigate the changes of ribbon synapses (RS) number in cochlear hair cells in C57BL/6J mice with age. Basilar membranes within the cochlea of C57BL/6J mice aged 2, 6, 10 and 12 months were harvested (5 mice in each age group). The presynaptic and postsynaptic membranes were subject to double immunohistochemical staining and observed with a laser confocal microscope. The number of RS in each segment of basilar membrane was counted by using 3D reconstruction technique. Compared with 2-month-old mice, reduction of RS number in basilar membrane inside cochlea mainly occurred to the basal turn among C57BL/6J mice aged 6 months. The number of RS in each turn among 10-month-old mice decreased considerably, and such decrease continued in the top turn and middle turn in mice aged 12 months. In contrast, the number of RS in the basal turn increased slightly. Reduction of RS probably takes place in the early stage of C57BL/6J mice presbycusis. Early prevention of presbycusis can be achieved through measures to mitigate the reduction of RS.