Dendritic spines of CA 1 pyramidal cells in the rat hippocampus: serial electron microscopy with reference to their biophysical characteristics

By Km Harris, J. Stevens. 1989

Serial electron microscopy and 3-D reconstructions of dendritic spines from hippocampal area CA 1 dendrites were obtained to evaluate 2 questions about relationships between spine geometry and synaptic efficacy. First, under what biophysical conditions are the spine necks likely to reduce the magnitude of charge transferred from the synapses on the spine heads to the recipient dendrite? Simulation software provided by Charles Wilson (1984) was used to determine that if synaptic conductance is 1 nS or less, only 1% of the hippocampal spine necks are sufficiently thin and long to reduce charge transfer by more than 10%. If synaptic conductance approaches 5 nS, however, 33% of the hippocampal spine necks are sufficiently thin and long to reduce charge transfer by more than 10%. Second, is spine geometry associated with other anatomical indicators of synaptic efficacy, including the area of the postsynaptic density and the number of vesicles in the presynaptic axon? Reconstructed spines were graphically edited into head and neck compartments, and their dimensions were measured, the areas of the postsynaptic densities (PSD) were measured, and all of the vesicles in the presynaptic axonal varicosities were counted. The dimensions of the spine head were well correlated with the area of PSD and the number of vesicles in the presynaptic axonal varicosity. Spine neck diameter and length were not correlated with PSD area, head volume, or the number of vesicles. These results suggest that the dimensions of the spine head, but not the spine neck, reflect differences in synaptic efficacy. We suggest that the constricted necks of hippocampal dendritic spines might reduce diffusion of activated molecules to neighboring synapses, thereby attributing specificity to activated or potentiated synapses.

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Citations in the corpus

On the origin of the extracellular action potential waveform: A modeling study. (2006, methodology): “As is given by As L where L is the length of the compartment (in m), is the density of spines at the compartment location (in spines/ m), and is the average area of a spine, assumed to be 0.83 m2 (Harris and Stevens 1989).”
Anatomical and physiological plasticity of dendritic spines. (2007, background): “However, for the vast majority of spines, the effect on synaptically evoked electrical signals is expected to be inconsequential (Segev & Rall 1988, Harris & Stevens 1989, Koch & Zador 1993, Svoboda et al. 1996).”
Nanoconnectomic upper bound on the variability of synaptic plasticity (2015, background): “…the skewed shape of the frequency histograms, and the number of synapses per unit of volume (Figures 1–3), are consistent with previous observations (Harris and Stevens, 1989; Schikorski and Stevens, 1997; Sorra et al., 2006; Bourne and Harris, 2011; Bourne et al., 2013; Bell et al., 2014).”
Dendritic excitability and synaptic plasticity. (2008, unknown): “It is, for example, well established that several parameters reflecting synapse size (274, 275, 502, 565, 597, 670, 739, 767, 768) are correlated with synaptic strength (although see Refs.”
Dynamic Stochastic Synapses as Computational Units (1997, background): “By contrast, synapses from hippocampal region CA3 to region CA1 pyramidal neurons are often mediated by a single release site ( Harris & Stevens, 1989 ).”
Structural and molecular remodeling of dendritic spine substructures during long-term potentiation (2014, background): “The amount of these PSD proteins reached a level that is proportional and closer to the new spine volume, suggesting that the spine eventually recovers the natural correlation between the volume and the PSD size as seen in naive tissue (Harris and Stevens, 1989).”
Rapid Redistribution of Synaptic PSD-95 in the Neocortex In Vivo (2006, background): “]. Spines vary in size, and their volumes are proportional to the area of the PSD [”
Compartmentalizing the neuronal plasma membrane from axon initial segments to synapses. (2009, background): “Presynaptic boutons expand in size together with active zones, also the number of SVs increases, dendritic spines grow, and the PSD expands (Harris and Stevens, 1989; Pierce and Mendell, 1993; Schikorski and Stevens, 1997).”
Volume electron microscopy for neuronal circuit reconstruction. (2012, unknown): “For example, dendritic spine necks in the mammalian central nervous system can be as fine as 40 nm in diameter [2], and the fine neurites of the fruit fly Drosophila melanogaster can be as thin as 50 nm in diameter [1].”