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Dimensions and density of dendritic spines from rat dentate granule cells based on reconstructions from serial electron micrographs
Author(s) -
Trommald Mari,
Hulleberg Gunn
Publication year - 1997
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/(sici)1096-9861(19970106)377:1<15::aid-cne3>3.0.co;2-m
Subject(s) - dendritic spine , anatomy , granule (geology) , postsynaptic potential , granule cell , electron micrographs , dentate gyrus , spine (molecular biology) , long term potentiation , ultrastructure , electron microscope , biology , biophysics , neuroscience , chemistry , materials science , hippocampus , physics , optics , hippocampal formation , composite material , microbiology and biotechnology , biochemistry , receptor
In the hippocampus, most excitatory synapses are located on dendritic spines. It has been postulated that the geometry of spines and/or the postsynaptic density (PSD) influences synaptic efficiency and may contribute to the expression of plastic processes such as learning or long‐term potentiation (LTP). Based on three‐dimensional reconstructions of dentate granule cell dendrites from serial electron micrographs, we have measured head dimensions, neck cross‐sectional areas, neck length, and PSD area and form of 115 spines of dentate granule cells in the medial perforant path termination zone. All dimensions showed a large variability, with up to 100‐fold differences in values. A calculated diffusion index for transport of molecules through the reconstructed neck varied over a 100‐fold range. The neck and head dimensions were moderately positively correlated, whereas the PSD area was strongly correlated with head volume. Distribution histograms and scatter plots of various spine dimensions did not reveal any systematic clustering, suggesting that there is a continuum of spine geometries rather than distinct classes for granule cell dendritic spines in the middle molecular layer. Transversely (n = 13) and longitudinally (n = 27) sectioned dendrites had mean spine densities of 2.66 and 1.01 spines/μm, respectively, uncorrected for so‐called hidden spines. Bifurcating spines made up 2.1% of the total spine number in transversely and 2.3% in longitudinally sectioned dendrites. The twin spine heads never shared the same presynaptic bouton. Fenestrated or split PSDs shared the same presynaptic element in all but two cases, arguing against PSD division as an intermediate step in synapse formation. J. Comp. Neurol. 377:15‐28, 1997. © 1997 Wiley‐Liss, Inc.