To explore the relationship between age-related hearing loss (presbycusis) and synaptic degeneration in the hippocampal CA3 region of C57BL/6J mice, we investigated both cognitive performance and synaptic changes within the hippocampus of C57BL/6J mice from three age groups of 6-8,24-26, and 42-44 weeks; CBA/CaJ mice served as controls. The auditory brainstem response was used as a measure of hearing threshold, and cognitive behavior was evaluated using the Morris water maze. The ultrastructure of synapses was observed with transmission electron microscopy, and the quantity and distribution of the synaptic markers synaptophysin and PSD-95 were observed with immunohistochemistry. The hearing threshold of C57BL/61 mice was significantly higher at 24-26 weeks than at 6-8 weeks, and hearing loss was profound at 42-44 weeks. This was accompanied by progressive degeneration of synapses within the auditory cortex. In contrast, the hearing threshold of CBA/CaJ mice was relatively unchanged at 24-26 weeks of age, and these mice developed only mild hearing loss at 42-44 weeks of age. Interestingly, C57BL/6J, but not CBA/CaJ mice clearly exhibited both decreased performance in the Morris water maze and degeneration of synapses within the hippocampus. We therefore conclude that age-related hearing loss is accompanied by the degeneration of synapses in the hippocampal CA3 region of C57BL/6J mice. (C) 2011 Elsevier Inc. All rights reserved.
[1]Fudan Univ, Dept Otol & Skull Base Surg, Eye Ear Nose & Throat Hosp, Shanghai 200031, Peoples R China.
[2]Soochow Univ, Dept Otolaryngol, Affiliated Hosp 1, Suzhou 215006, Peoples R China.
[3]Fudan Univ, Inst Brain Sci, Shanghai 200031, Peoples R China.
[4]Shanghai Jiao Tong Univ, Sch Med, Dept Anat, Shanghai 200025, Peoples R China.
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