3D ultrastructural study of synapses using FIB/SEM of upper layers from the human Entorhinal Cortex (v1)

The entorhinal cortex (EC) is a brain region located on the anterior part of the medial temporal lobe which has been shown to be essential for memory functions and spatial navigation. Mapping the EC connectivity may contribute to the understanding of its structural design. One possible approach to decipher EC connectivity is its analysis at the ultrastructural level, using electron microscopy, to map synaptic contacts (synapses). Thus, a detailed ultrastructural analysis to map true synaptic contacts (or synapses) using 3D electron microscopy could contribute to a better understanding of the human cerebral cortex organization.
We used Focused Ion Beam/Scanning Electron Microscopy (FIB/SEM) to perform a 3D analysis of the synapses in the neuropil in layers 1, 2 (subdivisions 2-is and 2-ni) and 3 of the medial Entorhinal Cortex (MEC). 3 human brain autopsies cases (AB2, AB7, and M16) have been used to obtain a total of 36 FIB/SEM valid image stacks.
Specifically, we studied synaptic junctions, which were fully reconstructed in 3D. We analyzed the synaptic density, 3D spatial distribution, and type (excitatory and inhibitory), as well as the shape and size of each synaptic junction. Moreover, their postsynaptic targets were determined. Present data are intended to complete a detailed description of the synaptic organization of the human medial Entorhinal Cortex to better understand its functional organization.