Campbell G, Frost D O
Section of Neuroanatomy, Yale Medical School, New Haven, Connecticut 06510.
J Comp Neurol. 1988 Jun 15;272(3):383-408. doi: 10.1002/cne.902720308.
These experiments examine which morphological features of axon terminals and their synaptic glomeruli are determined by afferent axons, and which by their targets. In normal, adult hamsters, electron microscopy reveals that, with respect to multiple ultrastructural features, the terminals and synaptic glomeruli of retinal afferent axons in the dorsal lateral geniculate nucleus differ from those of ascending auditory and somatosensory afferents in the medial geniculate and ventrobasal nuclei, respectively. These features include: (1) the location of specific sensory axon terminals on the somata and dendrites of their targets neurons, (2) the constitutents of the glomeruli and their synaptic relationships, (3) the number of specific sensory terminal boutons per glomerulus, (4) bouton size, (5) the number of dendritic and somatic appendages contacted by each bouton, and (6) the mitochondrial morphology of the specific sensory afferent boutons. In order to ascertain which of these features are determined by afferent axons and which by their targets, we subjected newborn Syrian hamsters to surgical procedures known to produce permanent, abnormal retinal projections to the main thalamic auditory (medial geniculate) and somatosensory (ventrobasal) nuclei. When the animals were adults, we examined the terminals and synaptic glomeruli of abnormal retino-auditory and retino-somatosensory axons that were anterogradely labeled by intraocular injection of horseradish peroxidase. With respect to all of the preceding features except mitochondrial morphology, the terminals and synaptic glomeruli of retino-medial geniculate and retino-ventrobasal axons more nearly resembled those of normal, auditory and somatosensory afferent axons, respectively, than they did those of normal, retino-lateral geniculate axons. These results demonstrate that the differentiation of all the features that we have examined, except mitochondrial morphology, is determined by factors in target neurons or their environment. This finding suggests that the differentiation of morphological features involved in contacts among neurons (including the type, number and size of interconnected neuronal elements and the loci at which they contact each other) is responsive to interactions among the connected elements, or between neural elements and their environment (e.g., glia, extracellular matrix), whereas the differentiation of structures reflecting intrinsic functions of individual neuronal elements is not responsive to such interactions.
这些实验研究了轴突终末及其突触小球的哪些形态学特征由传入轴突决定，哪些由其靶标决定。在正常成年仓鼠中，电子显微镜观察显示，就多种超微结构特征而言，背侧外侧膝状核中视网膜传入轴突的终末和突触小球分别不同于内侧膝状核和腹侧基底核中上行听觉和躯体感觉传入轴突的终末和突触小球。这些特征包括：（1）特定感觉轴突终末在其靶神经元的胞体和树突上的位置；（2）小球的组成成分及其突触关系；（3）每个小球中特定感觉终末小体的数量；（4）小体大小；（5）每个小体接触的树突和胞体附属物的数量；（6）特定感觉传入小体的线粒体形态。为了确定这些特征中哪些由传入轴突决定，哪些由其靶标决定，我们对新生叙利亚仓鼠进行了手术操作，已知该操作会使视网膜向主要丘脑听觉（内侧膝状核）和躯体感觉（腹侧基底核）核团产生永久性异常投射。当动物成年后，我们检查了通过眼内注射辣根过氧化物酶顺行标记的异常视网膜 - 听觉和视网膜 - 躯体感觉轴突的终末和突触小球。就除线粒体形态外的所有上述特征而言，视网膜 - 内侧膝状核和视网膜 - 腹侧基底核轴突的终末和突触小球分别比正常视网膜 - 外侧膝状核轴突的终末和突触小球更类似于正常听觉和躯体感觉传入轴突的终末和突触小球。这些结果表明，除线粒体形态外，我们所研究的所有特征的分化均由靶神经元或其环境中的因素决定。这一发现表明，参与神经元间接触的形态学特征的分化（包括相互连接的神经元成分的类型、数量和大小以及它们相互接触的位点）对连接成分之间或神经成分与其环境（如神经胶质、细胞外基质）之间的相互作用有反应，而反映单个神经元成分内在功能的结构分化对这种相互作用无反应。
