This study has used dense reconstructions from serial EM images to compare the neuropil ultrastructure and connectivity of aged and adult mice. The analysis used models of axons, dendrites, and their synaptic connections, reconstructed from volumes of neuropil imaged in layer 1 of the somatosensory cortex. This shows the changes to neuropil structure that accompany a general loss of synapses in a well-defined brain region. The loss of excitatory synapses was balanced by an increase in their size such that the total amount of synaptic surface, per unit length of axon, and per unit volume of neuropil, stayed the same. There was also a greater reduction of inhibitory synapses than excitatory, particularly those found on dendritic spines, resulting in an increase in the excitatory/inhibitory balance. The close correlations, that exist in young and adult neurons, between spine volume, bouton volume, synaptic size, and docked vesicle numbers are all preserved during aging. These comparisons display features that indicate a reduced plasticity of cortical circuits, with fewer, more transient, connections, but nevertheless an enhancement of the remaining connectivity that compensates for a generalized synapse loss.
Bibliographical noteFunding Information:
The study was supported by a Novartis Biomedical Foundation grant, and a Swiss National Science Foundation grant to Graham Knott. The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
© 2018 Calì et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
ASJC Scopus subject areas
- Agricultural and Biological Sciences(all)
- Biochemistry, Genetics and Molecular Biology(all)
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Wawrzyniak, M. (Creator), Becker, C. (Creator), Maco, B. (Creator), Cantoni, M. (Creator), Jorstad, A. (Creator), Nigro, B. (Creator), Grillo, F. (Creator), De Paola, V. (Creator), Fua, P. (Creator), Knott, G. W. (Creator), Cali, C. (Creator), Wawrzyniak, M. (Creator), Becker, C. (Creator), Maco, B. (Creator), Cantoni, M. (Creator), Jorstad, A. (Creator), Nigro, B. (Creator), Grillo, F. (Creator), De Paola, V. (Creator), Fua, P. (Creator), Knott, G. W. (Creator) & Cali, C. (Creator), Dryad Digital Repository, May 17 2019