Sultemeier David R, Hoffman Larry F
Department of Head and Neck Surgery, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States.
Brain Research Institute, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States.
Front Cell Neurosci. 2017 Oct 27;11:331. doi: 10.3389/fncel.2017.00331. eCollection 2017.
Although the effects of aminoglycoside antibiotics on hair cells have been investigated for decades, their influences on the dendrites of primary afferent neurons have not been widely studied. This is undoubtedly due to the difficulty in disassociating pathology to dendritic processes from that resulting from loss of the presynaptic hair cell. This was overcome in the present investigation through development of a preparation using that enabled direct perilymphatic infusion. Through this strategy we unmasked gentamicin's potential effects on afferent calyces. The pathophysiology of the vestibular neuroepithelia after post-administration durations of 0.5 through 6 months was assessed using single-neuron electrophysiology, immunohistochemistry, and confocal microscopy. Hair cell densities within cristae central zones (0.5-, 1-, 2-, and 6-months) and utricle peri- and extrastriola (6-months) regions were determined, and damage to calretinin-immunoreactive calyces was quantified. Gentamicin-induced hair cell loss exhibited a profile that reflected elimination of a most-sensitive group by 0.5-months post-administration (18.2%), followed by loss of a second group (20.6%) over the subsequent 5.5 months. The total hair cell loss with this gentamicin dose (approximately 38.8%) was less than the estimated fraction of type I hair cells in the chinchilla's crista central zone (approximately 60%), indicating that viable type I hair cells remained. Extensive lesions to afferent calyces were observed at 0.5-months, though stimulus-evoked modulation was intact at this post-administration time. Widespread compromise to calyx morphology and severe attenuation of stimulus-evoked afferent discharge modulation was found at 1 month post-administration, a condition that persisted in preparations examined through the 6-month post-administration interval. Spontaneous discharge was robust at all post-administration intervals. All calretinin-positive calyces had retracted at 2 and 6 months post-administration. We found no evidence of morphologic or physiologic recovery. These results indicate that gentamicin-induced partial lesions to vestibular epithelia include hair cell loss (ostensibly reflecting an ) that is far less extensive than the compromise to stimulus-evoked afferent discharge modulation and retraction of afferent calyces (reflecting ). Additionally, calyx retraction cannot be completely accounted for by loss of type I hair cells, supporting the possibility for direct action of gentamicin on the afferent dendrite.
尽管氨基糖苷类抗生素对毛细胞的影响已被研究了数十年，但其对初级传入神经元树突的影响尚未得到广泛研究。这无疑是由于难以将树突病理过程与突触前毛细胞丧失所导致的病理过程区分开来。在本研究中，通过开发一种能够直接进行外淋巴灌注的制备方法克服了这一困难。通过这种策略，我们揭示了庆大霉素对传入杯状终器的潜在影响。使用单神经元电生理学、免疫组织化学和共聚焦显微镜评估了给药后0.5至6个月内前庭神经上皮的病理生理学。确定了嵴中央区（0.5个月、1个月、2个月和6个月）以及椭圆囊周边和条纹外区（6个月）的毛细胞密度，并对钙视网膜蛋白免疫反应性杯状终器的损伤进行了量化。庆大霉素诱导的毛细胞丧失呈现出一种模式，即在给药后0.5个月时最敏感的一组毛细胞被消除（18.2%），随后在接下来的5.5个月内第二组毛细胞丧失（20.6%）。该剂量庆大霉素导致的毛细胞总丧失率（约38.8%）低于豚鼠嵴中央区I型毛细胞的估计比例（约60%），表明仍有存活的I型毛细胞。在给药后0.5个月时观察到传入杯状终器有广泛损伤，不过在这个给药后时间点刺激诱发的调制是完整的。在给药后1个月时发现杯状终器形态广泛受损且刺激诱发的传入放电调制严重减弱，这种情况在给药后6个月内检查的标本中持续存在。在所有给药后时间间隔内自发放电都很强烈。在给药后2个月和6个月时，所有钙视网膜蛋白阳性的杯状终器都已退缩。我们没有发现形态或生理恢复的证据。这些结果表明，庆大霉素诱导的前庭上皮部分损伤包括毛细胞丧失（表面上反映了一种情况），其程度远小于刺激诱发的传入放电调制受损和传入杯状终器退缩（反映了另一种情况）。此外，杯状终器退缩不能完全由I型毛细胞丧失来解释，这支持了庆大霉素对传入树突有直接作用的可能性。
