Avwenagha O, Bird M M, Lieberman A R, Yan Q, Campbell G
Department of Anatomy and Developmental Biology, University College London, Gower Street, London WC1E 6BT, UK.
Neuroscience. 2006 Jul 7;140(3):913-28. doi: 10.1016/j.neuroscience.2006.02.056. Epub 2006 Apr 19.
We have examined the cellular and subcellular distribution and the patterns of expression of brain-derived neurotrophic factor (BDNF), and of its high affinity receptor, tyrosine kinase B (TrkB), in retinorecipient regions of the brain, including the superior colliculus, the lateral geniculate nucleus and the olivary pretectal nucleus. In the retinorecipient layers of the superior colliculus, BDNF protein and mRNA were present in the cell bodies of a subpopulation of neurons, and BDNF protein was present in the neuropil as punctate or fiber-like structures. In the lateral geniculate nucleus, however, BDNF mRNA was not detected, and BDNF protein was restricted to punctate and fiber-like structures in the neuropil, especially in the most superficial part of the dorsal lateral geniculate nucleus, just below the optic tract. At the ultrastructural level, BDNF protein was localized predominantly to axon terminals containing round synaptic vesicles and pale mitochondria with irregular cristae, which made asymmetric (Gray type I) synaptic specializations (R-boutons). Enucleation of one eye was followed by loss of BDNF immunoreactivity and disappearance of BDNF-positive R-boutons in the contralateral visual centers, confirming the retinal origin of at least most of these terminals. TrkB was present in postsynaptic densities apposed to immunoreactive R-boutons in the superior colliculus and lateral geniculate nucleus, and was also associated with axonal and dendritic microtubules. These findings suggest that BDNF is synthesized by a subpopulation of retinal ganglion cells and axonally transported to visual centers where this neurotrophin is assumed to play important roles in visual system maintenance and/or in modulating the excitatory retinal input to neurons in these centers.
我们研究了脑源性神经营养因子（BDNF）及其高亲和力受体酪氨酸激酶B（TrkB）在脑内视网膜接受区的细胞和亚细胞分布以及表达模式，这些区域包括上丘、外侧膝状体核和橄榄前顶盖核。在上丘的视网膜接受层中，BDNF蛋白和mRNA存在于一部分神经元的细胞体中，并且BDNF蛋白在神经毡中以点状或纤维状结构存在。然而，在外侧膝状体核中未检测到BDNF mRNA，BDNF蛋白局限于神经毡中的点状和纤维状结构，特别是在背外侧膝状体核最表层，恰好在视束下方。在超微结构水平上，BDNF蛋白主要定位于含有圆形突触小泡和具有不规则嵴的浅色线粒体的轴突终末，这些终末形成不对称（Gray I型）突触特化（R型终扣）。单眼摘除后，对侧视觉中枢中BDNF免疫反应性丧失且BDNF阳性R型终扣消失，证实了这些终末至少大部分起源于视网膜。TrkB存在于上丘和外侧膝状体核中与免疫反应性R型终扣相对的突触后致密部，并且还与轴突和树突微管相关。这些发现表明BDNF由一部分视网膜神经节细胞合成并通过轴突运输至视觉中枢，在这些中枢中这种神经营养因子被认为在视觉系统维持和/或调节视网膜对这些中枢神经元的兴奋性输入中发挥重要作用。
