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8 results on '"Cano-Astorga, Nicolás"'

1. Unambiguous identification of asymmetric and symmetric synapses using volume electron microscopy.

Author

Cano-Astorga, Nicolás, Plaza-Alonso, Sergio, Turegano-Lopez, Marta, Rodrigo-Rodríguez, José, Merchan-Perez, Angel, and DeFelipe, Javier

Subjects
SYNAPSES, ELECTRON microscopy, GABA transporters, FOCUSED ion beams, ELECTRON density, CEREBRAL cortex, CELL membranes
Abstract

The brain contains thousands of millions of synapses, exhibiting diverse structural, molecular, and functional characteristics. However, synapses can be classified into two primary morphological types: Gray's type I and type II, corresponding to Colonnier's asymmetric (AS) and symmetric (SS) synapses, respectively. AS and SS have a thick and thin postsynaptic density, respectively. In the cerebral cortex, since most AS are excitatory (glutamatergic), and SS are inhibitory (GABAergic), determining the distribution, size, density, and proportion of the two major cortical types of synapses is critical, not only to better understand synaptic organization in terms of connectivity, but also from a functional perspective. However, several technical challenges complicate the study of synapses. Potassium ferrocyanide has been utilized in recent volume electron microscope studies to enhance electron density in cellular membranes. However, identifying synaptic junctions, especially SS, becomes more challenging as the postsynaptic densities become thinner with increasing concentrations of potassium ferrocyanide. Here we describe a protocol employing Focused Ion Beam Milling and Scanning Electron Microscopy for studying brain tissue. The focus is on the unequivocal identification of AS and SS types. To validate SS observed using this protocol as GABAergic, experiments with immunocytochemistry for the vesicular GABA transporter were conducted on fixed mouse brain tissue sections. This material was processed with different concentrations of potassium ferrocyanide, aiming to determine its optimal concentration. We demonstrate that using a low concentration of potassium ferrocyanide (0.1%) improves membrane visualization while allowing unequivocal identification of synapses as AS or SS. [ABSTRACT FROM AUTHOR] more...

Published
2024
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2. Cortical synapses of the world's smallest mammal: An FIB/SEM study in the Etruscan shrew

Author

Ministerio de Ciencia e Innovación (España), Alonso-Nanclares, Lidia, Rodrigo Rodríguez, J., Merchán-Pérez, Ángel, González-Soriano, Juncal, Plaza-Alonso, Sergio, Cano-Astorga, Nicolás, Naumann, Robert K., Brecht, Michael, DeFelipe, Javier, Ministerio de Ciencia e Innovación (España), Alonso-Nanclares, Lidia, Rodrigo Rodríguez, J., Merchán-Pérez, Ángel, González-Soriano, Juncal, Plaza-Alonso, Sergio, Cano-Astorga, Nicolás, Naumann, Robert K., Brecht, Michael, and DeFelipe, Javier more...

Abstract

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. We analyzed the cortical synaptic density and a variety of structural characteristics of 7,239 3D reconstructed synapses, using using Focused Ion Beam/Scanning Electron Microscopy (FIB/SEM). We found that some of the 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. more...

Published
2023

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7. 3D Analysis of the Synaptic Organization in the Entorhinal Cortex in Alzheimer's Disease

Author

Domínguez-Álvaro, M., Montero-Crespo, M., Blázquez-Llorca, Lidia, Plaza-Alonso, Sergio, Cano-Astorga, Nicolás, DeFelipe, Javier, Alonso-Nanclares, Lidia, Domínguez-Álvaro, M., Montero-Crespo, M., Blázquez-Llorca, Lidia, Plaza-Alonso, Sergio, Cano-Astorga, Nicolás, DeFelipe, Javier, and Alonso-Nanclares, Lidia more...

Abstract

The entorhinal cortex (EC) is especially vulnerable in the early stages of Alzheimer's disease (AD). In particular, cognitive deficits have been linked to alterations in the upper layers of EC. In the present report, we examined Layers II and III from eight human brain autopsies (four subjects with no recorded neurologic alterations and four AD cases). We used stereological methods to assess cortical atrophy of the EC and possible changes in the volume occupied by different cortical elements (neuronal and glial cell bodies; blood vessels; and neuropil). We performed 3D ultrastructural analyses of synapses using focused ion beam/scanning electron microscopy (FIB/SEM) to examine possible alterations related to AD. At the light microscope level, we found a significantly lower volume fraction occupied by neuronal bodies in Layer III and a higher volume fraction occupied by glial cell bodies in Layer II in AD cases. At the ultrastructural level, we observed that (1) there was a significantly lower synaptic density in both layers in AD cases; (2) synapses were larger and more complex in Layer II in AD cases; and (3) there was a greater proportion of small and simple synapses in Layer III in AD cases than in control individuals. These structural differences may play a role in the anatomic basis for the impairment of cognitive functions in AD. more...

Published
2021