Catania S, Germanà A, Cabo R, Ochoa-Erena F J, Guerrera M C, Hannestad J, Represa J, Vega J A
Dipartimento di Morfologia, Biochimica, Fisiologia e Produzione Animale, Università di Messina, Italy.
J Anat. 2007 Jan;210(1):78-88. doi: 10.1111/j.1469-7580.2006.00673.x.
Neurotrophins (NTs) and their signal transducing Trk receptors play a critical role in the development and maintenance of specific neuronal populations in the nervous system of higher vertebrates. They are responsible for the innervation of the inner ear cochlear and vestibular sensory epithelia. Neurotrophins and Trks are also present in teleosts but their distribution in the inner ear is unknown. Thus, in the present study, we used Western-blot analysis and immunohistochemistry to investigate the expression and cell localization of both NTs and Trk receptors in the inner ear of alevins of Salmo salar and Salmo trutta. Western-blot analysis revealed the occurrence of brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3), but not nerve growth factor (NGF), as well as all three Trk receptors, i.e. TrkA, TrkB and TrkC, the estimated molecular weights of which were similar to those expected for mammals. Specific immunoreactivity for neurotrophins was detected mainly in the sensory epithelia. In particular, BDNF immunoreactivity was found in the maculae of the utricle and saccule, whereas NT-3 immunoreactivity was present in the sensory epithelium of the cristae ampullaris. As a rule the sensory epithelia of the inner ear lacked immunoreactivity for Trks, thus excluding possible mechanisms of autocrinia and/or paracrinia. By contrast, overlapping subpopulations of neurons in the statoacoustic ganglion expressed TrkA (about 15%), TrkB (about 65%) and TrkC (about 45%). The present results demonstrate that, as in mammals and birds, the inner ear of teleosts expresses the components of the neurotrophin-Trk system, but their roles remain to be elucidated.
神经营养因子（NTs）及其信号转导Trk受体在高等脊椎动物神经系统中特定神经元群体的发育和维持中起着关键作用。它们负责内耳耳蜗和前庭感觉上皮的神经支配。神经营养因子和Trk受体在硬骨鱼中也存在，但其在内耳中的分布尚不清楚。因此，在本研究中，我们使用蛋白质免疫印迹分析和免疫组织化学来研究挪威三文鱼和褐鳟仔鱼内耳中NTs和Trk受体的表达及细胞定位。蛋白质免疫印迹分析显示存在脑源性神经营养因子（BDNF）和神经营养因子-3（NT-3），但不存在神经生长因子（NGF），以及所有三种Trk受体，即TrkA、TrkB和TrkC，其估计分子量与哺乳动物预期的分子量相似。神经营养因子的特异性免疫反应主要在感觉上皮中检测到。特别是，BDNF免疫反应性存在于椭圆囊和球囊的斑中，而NT-3免疫反应性存在于壶腹嵴的感觉上皮中。通常，内耳的感觉上皮缺乏Trk的免疫反应性，因此排除了自分泌和/或旁分泌的可能机制。相比之下，听神经节中重叠的神经元亚群表达TrkA（约15%）、TrkB（约65%）和TrkC（约45%）。目前的结果表明，与哺乳动物和鸟类一样，硬骨鱼的内耳表达神经营养因子-Trk系统的成分，但其作用仍有待阐明。
