Supplementary Material for: Calcium-Binding Proteins and Melatonin Receptors in the Central Auditory System of Aged Rats

Age-related hearing loss (ARHL) is a multifactorial disorder due to impairment in the peripheral or central auditory pathway (CAP). CAP impairment refers to difficulties in speech understanding, particularly in the presence of background noise, problems in discrimination, and integrating and separating binaural auditory information. Changes in CAP mechanisms, such as neurotransmitters or ion movement, may correlate with this impairment. The regulation of calcium (Ca2+) concentrations by Ca2+ binding proteins (CaBPs) is critical for synaptic function and plasticity, and changes are directly related to ARHL. Thus, changes in the neuronal expression of CaBPs in aging could be related to CAP disorders. Considering that supplementation with antioxidant and/or neuroprotective substances can delay neuronal loss in aging, antioxidant-based therapies can prevent and/or reduce the progression of ARHL in animal models and humans. The hormone melatonin has important antioxidant and neuroprotective actions, which can sometimes depend on melatonin receptors. This work aimed to investigate changes in the expression of CaBPs and melatonin receptors in the CAP stations and whether this expression could vary with aging. The analysis revealed a lower density of CaBP-immunoreactive cells in most CAP nuclei. In contrast, elderly rats showed increased expression of MT1 and MT2 in CAP stations. These findings suggest that changes in neuronal number and transmission in these nuclei in aging are concomitant with increased melatonin's potential sites of action in the CAP.年龄相关性听力损失（age-related hearing loss, ARHL）是一种多因素疾病，由外周或中枢听觉通路（peripheral or central auditory pathway, CAP）损伤所致。中枢听觉通路损伤特指言语理解困难，尤其是在背景噪声环境下的言语理解障碍，同时可出现辨别能力缺陷以及双耳听觉信息的整合与分离障碍。中枢听觉通路的机制改变，如神经递质或离子转运异常，或与该损伤存在关联。钙离子（Ca²⁺）结合蛋白（Ca²⁺ binding proteins, CaBPs）对钙离子浓度的调控对于突触功能与突触可塑性至关重要，其表达变化与年龄相关性听力损失直接相关。因此，衰老过程中钙结合蛋白神经元表达的变化，或与中枢听觉通路障碍相关。鉴于补充抗氧化剂和/或神经保护物质可延缓衰老过程中的神经元丢失，基于抗氧化剂的治疗策略在动物模型与人类受试者中均可预防或延缓年龄相关性听力损失的进展。激素褪黑素具有重要的抗氧化与神经保护作用，其部分生物学效应依赖于褪黑素受体。本研究旨在探究中枢听觉通路各核团中钙结合蛋白与褪黑素受体的表达变化，以及该表达是否随衰老进程发生改变。分析结果显示，在多数中枢听觉通路核团中，钙结合蛋白免疫阳性细胞的密度显著降低。与之相反，老年大鼠的中枢听觉通路核团中MT1与MT2的表达水平显著升高。上述研究结果表明，衰老过程中这些核团的神经元数量与信号传递的变化，与中枢听觉通路中褪黑素潜在作用位点的增加相伴发生。