Mouse 3

Image stack and blender files with the 3D mesh data reconstructed from a 4 months old layer I somatosensory cortex neuropi

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Mouse 4

Image stack and blender files with the 3D mesh data reconstructed from a 24 months old layer I somatosensory cortex neuropi

Mouse 1

Image stack and blender files with the 3D mesh data reconstructed from a 4 months old layer I somatosensory cortex neuropi

Mouse 6

Image stack and blender files with the 3D mesh data reconstructed from a 4 months old layer I somatosensory cortex neuropi

Data from: The effects of aging on neuropil structure in mouse somatosensory cortex—A 3D electron microscopy analysis of layer 1

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

Mouse 5

Image stack and blender files with the 3D mesh data reconstructed from a 24 months old layer I somatosensory cortex neuropi

Synapse density per type.

<p>Synapse density per type.</p

Dense reconstructions of sub-volumes reveal the same amount of asymmetric synaptic surface area per unit length of axon and dendrite, and per unit volume of neuropil in adult and aged mice.

<p><b>A</b>, FIBSEM images were segmented in the Ilastik software (<a href="http://www.ilastik.org/" target="_blank">www.ilastik.org</a>) to reconstruct all the axons (shown in blue) and dendrites (in green). Synapses were segmented in the TrakEM2 software in FIJI (shown in red: <a href="http://www.fiji.sc/" target="_blank">www.fiji.sc</a>). <b>B</b>, These stacks were sub-volumes from the larger ones used for synapse density measurements (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0198131#pone.0198131.g002" target="_blank">Fig 2A</a>) and had side lengths of 5μm (volumes of 25 μm³). All axons, dendrites and synapses were reconstructed in six of these cubes (3 adults, 3 aged). <b>C</b>, Average synaptic surface area shows a significant increase in aged animals (adult, N = 313 synapses 0.15 ± 0.007 μm² per μm³; aged, N = 288 synapses 0.17 ± 0.008 μm² per μm³; Kolmogorov-Smirnov test, p = 0.04). <b>D</b>, Analysis of neurite lengths shows that layer 1 neuropil of aged mice contained significantly more micrometers of axon per cubic micrometer of neuropil (8.15 ± 0.19 μm of axons per μm³ for adults; 10.27 ± 0.88 μm of axons per μm³ for aged; p = 0.016, unpaired t-test). The dendritic content was smaller but non-significant (1.37 ± 0.06 μm of dendrites per μm³ for adults; 1.53 ± 0.12 μm of dendrites per μm³ for aged; p = 0.3, unpaired t-test). <b>E</b>, Number of asymmetric synapses per unit length of axon was 32.9% less in aged mice (adult, 0.173 ± 0.005 synapses per μm of axons; aged, 0.116 ± 0.011 synapses per μm of axons; t-test, p = 0.008). Numbers of asymmetric synapses per unit length of dendrite was 24.6% less in aged mice (adult, 1.03 ± 0.046 synapses per μm of dendrite; aged, 0.776 ± 0.072 synapses per μm of dendrite; t-test, p = 0.04). <b>F</b>, Asymmetric synaptic surface area per unit length of axons or dendrites was not significantly different mice (adult, 0.065 ± 0.012 μm² per μm of axons; aged, 0.055 ± 0.007 μm² per μm of axons; unpaired t-test, p = 0.53; adult, 0.144 ± 0.026 μm² per μm of dendrites; aged, 0.126 ± 0.014 μm² per μm of dendrites; unpaired t-test, p = 0.57). <b>G</b>, Asymmetric synaptic surface per unit volume also showed no difference between the adult and aged mice (adult, 0.19 ± 0.03 μm² per μm³; aged, 0.19 ± 0.012 μm² per μm³; t-test, p = 0.9).</p

Measurements on saturated reconstructions.

<p>Measurements on saturated reconstructions.</p