Steward O, Falk P M
J Neurosci Res. 1985;13(1-2):75-88. doi: 10.1002/jnr.490130106.
We have previously reported that there is a dramatic increase in polyribosomes associated with dendritic spines during periods of synapse growth induced by denervating lesions. We suggested that polyribosomes at the postsynaptic site may somehow be involved in the growth of synapses. To evaluate this hypothesis further, the present study determines whether synapses which are growing in the developmental period also have accumulations of polyribosomes. We examined the dentate gyrus of the developing rat electron microscopically at 7, 10, 15, 20, and 28 days of age, which spans the major period of synaptogenesis in this structure. Qualitative observations revealed dramatic accumulations of polyribosomes under spine synapses in the youngest animals (7 and 10 days of age). With synapse development, the accumulations of polyribosomes became less dramatic, so that by 28 days of age, the neuropil of the dentate gyrus appeared qualitatively mature. To determine the relationship between polyribosomes under spine synapses and synapse development, quantitative electron microscopic methods were use to evaluate synapse density (number of synapses/100 micron 2), and the incidence of polyribosome-containing spines (proportion of spine synapses with underlying polyribosomes) in the neuropil of the dorsal blade of the dentate gyrus at each age. An inverse relationship was found between synapse density and the proportion of spines with polyribosomes. Synapse density increased in an almost linear fashion between 7 and 28 days of age to levels which were actually somewhat higher than in mature rats, whereas the incidence of polyribosome-containing spines was highest at the youngest ages and decreased with development. Thus, polyribosomes were most prominent under spine synapses during the period of maximal synapse growth. These results, together with our previous observations of increased numbers of polyribosomes under spines during lesion-induced growth, suggest that the polyribosomes represent a structural specialization of dendrites at sites of synapse construction. We propose that they produce protein(s) that are involved in synapse growth.
我们之前曾报道，在去神经损伤诱导的突触生长期间，与树突棘相关的多核糖体显著增加。我们推测突触后位点的多核糖体可能以某种方式参与突触的生长。为了进一步评估这一假设，本研究确定在发育阶段生长的突触是否也有多核糖体的积累。我们在7、10、15、20和28日龄时对发育中的大鼠齿状回进行了电子显微镜检查，这涵盖了该结构突触形成的主要时期。定性观察显示，在最年幼的动物（7和10日龄）中，棘突触下有大量多核糖体积累。随着突触的发育，多核糖体的积累变得不那么显著，因此到28日龄时，齿状回的神经毡在质量上似乎已经成熟。为了确定棘突触下的多核糖体与突触发育之间的关系，我们使用定量电子显微镜方法评估每个年龄齿状回背叶神经毡中的突触密度（突触数量/100平方微米）以及含有多核糖体的棘的发生率（有潜在多核糖体的棘突触的比例）。我们发现突触密度与有多核糖体的棘的比例呈负相关。在7至28日龄之间，突触密度几乎呈线性增加，达到实际上比成年大鼠略高的水平，而含有多核糖体的棘的发生率在最年幼时最高，并随着发育而降低。因此，在突触最大生长期间，多核糖体在棘突触下最为突出。这些结果，连同我们之前对损伤诱导生长期间棘下多核糖体数量增加的观察结果，表明多核糖体代表了突触构建部位树突的一种结构特化。我们提出它们产生参与突触生长的蛋白质。
