Decision letter: Ultrastructural heterogeneity of layer 4 excitatory synaptic boutons in the adult human temporal lobe neocortex

Synapses are fundamental building blocks controlling and modulating the ‘behavior’ of brain networks. How their structural composition, most notably their quantitative morphology underlie their computational properties remains rather unclear, particularly in humans. Here, excitatory synaptic boutons (SBs) in layer 4 (L4) of the temporal lobe neocortex (TLN) were quantitatively investigated. Biopsies from epilepsy surgery were used for fine-scale and tomographic electron microscopy (EM) to generate 3D-reconstructions of SBs. Particularly, the size of active zones (AZs) and that of the three functionally defined pools of synaptic vesicles (SVs) were quantified. SBs were comparatively small (~2.50 μm2), with a single AZ (~0.13 µm2); preferentially established on spines. SBs had a total pool of ~1800 SVs with strikingly large readily releasable (~20), recycling (~80) and resting pools (~850). Thus, human L4 SBs may act as ‘amplifiers’ of signals from the sensory periphery, integrate, synchronize and modulate intra- and extracortical synaptic activity.

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Ultrastructural heterogeneity of human layer 4 excitatory synaptic boutons in the adult temporal lobe neocortex

10.1101/643924 ◽

2019 ◽

Author(s):

Rachida Yakoubi ◽

Astrid Rollenhagen ◽

Marec von Lehe ◽

Dorothea Miller ◽

Bernd Walkenfort ◽

...

Keyword(s):

Temporal Lobe ◽

Synaptic Vesicles ◽

Building Blocks ◽

Synaptic Activity ◽

Quantitative Morphology ◽

Layer 4 ◽

Total Pool ◽

Synaptic Boutons ◽

Active Zones ◽

Computational Properties

AbstractSynapses are fundamental building blocks that control and modulate the ‘behavior’ of brain networks. How their structural composition, most notably their quantitative morphology underlies their computational properties remains rather unclear, particularly in humans. Here, excitatory synaptic boutons (SBs) in layer 4 (L4) of the temporal lobe neocortex (TLN) were quantitatively investigated.Biopsies from epilepsy surgery were used for fine-scale and tomographic electron microscopy to generate 3D-reconstructions of SBs. Particularly, the size of active zones (AZs) and of the three functionally defined pools of synaptic vesicles (SVs) were quantified.SBs were comparably small (∼2.50 μm2), with a single AZ (∼0.13 µm2) and preferentially established on spines. SBs had a total pool of ∼1800SVs with strikingly large readily releasable (∼ 20), recycling (∼ 80) and resting pools (∼850).Thus, human L4 SBs may act as ‘amplifiers’ of signals from the sensory periphery and integrate, synchronize and modulate intra- and extra-cortical synaptic activity.

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Quantitative Three-Dimensional Reconstructions of Excitatory Synaptic Boutons in Layer 5 of the Adult Human Temporal Lobe Neocortex: A Fine-Scale Electron Microscopic Analysis

Cerebral Cortex ◽

10.1093/cercor/bhy146 ◽

2018 ◽

Vol 29 (7) ◽

pp. 2797-2814 ◽

Cited By ~ 15

Author(s):

Rachida Yakoubi ◽

Astrid Rollenhagen ◽

Marec von Lehe ◽

Yachao Shao ◽

Kurt Sätzler ◽

...

Keyword(s):

Temporal Lobe ◽

Three Dimensional ◽

Microscopic Analysis ◽

Synaptic Cleft ◽

Brain Regions ◽

Fine Scale ◽

Electron Microscopic ◽

Readily Releasable Pool ◽

Synaptic Boutons ◽

Human Temporal Lobe

Abstract Studies of synapses are available for different brain regions of several animal species including non-human primates, but comparatively little is known about their quantitative morphology in humans. Here, synaptic boutons in Layer 5 (L5) of the human temporal lobe (TL) neocortex were investigated in biopsy tissue, using fine-scale electron microscopy, and quantitative three-dimensional reconstructions. The size and organization of the presynaptic active zones (PreAZs), postsynaptic densities (PSDs), and that of the 3 distinct pools of synaptic vesicles (SVs) were particularly analyzed. L5 synaptic boutons were medium-sized (~6 μm2) with a single but relatively large PreAZ (~0.3 μm2). They contained a total of ~1500 SVs/bouton, ~20 constituting the putative readily releasable pool (RRP), ~180 the recycling pool (RP), and the remainder, the resting pool. The PreAZs, PSDs, and vesicle pools are ~3-fold larger than those of CNS synapses in other species. Astrocytic processes reached the synaptic cleft and may regulate the glutamate concentration. Profound differences exist between synapses in human TL neocortex and those described in various species, particularly in the size and geometry of PreAZs and PSDs, the large RRP/RP, and the astrocytic ensheathment suggesting high synaptic efficacy, strength, and modulation of synaptic transmission at human synapses.

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