The Journal of neuroscience : the official journal of the Society for Neuroscience
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It has long been hypothesized that changes in dendritic spine structure may modify the physiological properties of synapses located on them. Due to their small size, large number, and highly variable shapes, standard light microscopy of Golgi impregnations and electron microscopy (EM) of single thin sections have not proved adequate to identify most spines in a sample or to quantify their structural dimensions and composition. Here we describe a new approach, the series sample, that was developed to classify by shape and subcellular composition all of the spines and synapses in a sample of neuropil by viewing them through serial EM sections. ⋯ In addition, LTP is not likely to be mediated by widening of spine necks at either age. However, the constricted spine necks could serve to concentrate specific molecules at activated synapses, thereby enhancing the specificity and endurance of LTP with maturation. These results demonstrate that the new series sample method combined with three-dimensional reconstruction reveals quantitative changes in the frequency and structure of spines and synapses that are not discernable by other methods and are likely to have dramatic effects on synaptic physiology and plasticity.