Biology subjects

Plaza-Alonso, S.

Publications and source records attributed to Plaza-Alonso, S..

2 recordsLinked to original sources

bioRxiv2023

3D Synaptic Organization of Layer III of the Human Anterior Cingulate and Temporopolar Cortex

The human anterior cingulate and temporopolar cortices have been proposed as highly connected nodes involved in high-order cognitive functions, but their synaptic organization is still basically unknown due to the difficulties involved in studying the human brain. Using Focused Ion Beam/Scanning Electron Microscopy (FIB/SEM) to study the synaptic organization of the human brain obtained with a short post-mortem delay allows excellent results to be obtained. We have used this technology to analyze the neuropil (where the vast majority of synapses are found) of layer III of the anterior cingulate cortex (Brodmanns area 24) and the temporopolar cortex, including the temporal pole (Brodmanns area 38 ventral and dorsal) and anterior middle temporal gyrus (Brodmanns area 21). Our results, based on 6695 synapses fully reconstructed in 3D, revealed that Brodmanns areas 24, 21 and ventral area 38 showed similar synaptic density and synaptic size, whereas dorsal area 38 displayed the highest synaptic density and the smallest synaptic size. However, the proportion of the different types of synapses (excitatory and inhibitory), the postsynaptic targets and the shapes of excitatory and inhibitory synapses were similar, regardless of the region examined. These observations indicate that certain aspects of the synaptic organization are rather homogeneous, whereas others show specific variations across cortical regions. Since not all data obtained in a given cortical region can be extrapolated to other cortical regions, further studies on the other cortical regions and layers are necessary to better understand the functional organization of the human cerebral cortex.

neuroscience↗

bioRxiv2022

Cortical synapses of the world's smallest mammal: an FIB/SEM study in the Etruscan shrew

The main aim of the present study was to determine if synapses from the exceptionally small brain of the Etruscan shrew show any peculiarities compared to the much larger human brain. This study constitutes the first description of the Etruscan shrew synaptic characteristics using Focused Ion Beam/Scanning Electron Microscopy (FIB/SEM). We analyzed the synaptic density and a variety of structural characteristics of 7,239 3D reconstructed synapses, obtaining the following major results: (i) cortical synaptic density was very high, particularly in layer I; (ii) the vast majority of synapses were excitatory, with the highest proportion found in layer I; (iii) excitatory synapses were larger than inhibitory synapses in all layers except in layer VI; and (iv) synapses were either randomly distributed in space or showed a slight tendency to be organised in a regular arrangement. Some of these general synaptic characteristics are remarkably similar to those found in the human cerebral cortex. However, the cortical volume of the human brain is about 50,000 times larger than the cortical volume of the Etruscan shrew, while the total number of cortical synapses in human is only 20,000 times the number of synapses in the shrew, and synaptic junctions are 35% smaller in the Etruscan shrew. Thus, the differences in the number and size of synapses cannot be attributed to a brain size scaling effect but rather to adaptations of synaptic circuits to particular functions. The present work provides a quantitative dataset from the Etruscan shrew synapses -- not only contributing to the knowledge of the ultrastructure of the mammalian cortex, but also identifying common and differing principles of synaptic organization.

neuroscience↗