Comparative 2D and 3D Ultrastructural Analyses of Dendritic Spines from CA1 Pyramidal Neurons in the Mouse Hippocampus.

Maria Colombo,Sabrina Putignano,Greta Maiellano,Lucrezia Scandella,Maura Francolini

doi:10.3390/ijms22031188

Maria Colombo, Sabrina Putignano + Show 3 more

Open Access

https://doi.org/10.3390/ijms22031188

Copy DOI

Abstract

Three-dimensional (3D) reconstruction from electron microscopy (EM) datasets is a widely used tool that has improved our knowledge of synapse ultrastructure and organization in the brain. Rearrangements of synapse structure following maturation and in synaptic plasticity have been broadly described and, in many cases, the defective architecture of the synapse has been associated to functional impairments. It is therefore important, when studying brain connectivity, to map these rearrangements with the highest accuracy possible, considering the affordability of the different EM approaches to provide solid and reliable data about the structure of such a small complex. The aim of this work is to compare quantitative data from two dimensional (2D) and 3D EM of mouse hippocampal CA1 (apical dendrites), to define whether the results from the two approaches are consistent. We examined asymmetric excitatory synapses focusing on post synaptic density and dendritic spine area and volume as well as spine density, and we compared the results obtained with the two methods. The consistency between the 2D and 3D results questions the need—for many applications—of using volumetric datasets (costly and time consuming in terms of both acquisition and analysis), with respect to the more accessible measurements from 2D EM projections.

Highlights

Received: 28 December 2020The concept of the dendritic spine has undergone evolution since their discovery by the neuroanatomist Ramon Y Cajal, in 1888, who observed by means of light microscopy “thin protrusions” on the surface of a number of Golgi-impregnated neurons
The aim of our work is to evaluate whether analyses on single-section transmission electron microscopy (TEM) micrographs and reconstruction from 3D-electron microscopy (EM) stacks are reliable and give comparable results, when dendritic spines from asymmetric excitatory synapses in the central nervous system are qualitatively and quantitatively described
Despite the huge amount of details and information that were obtained from the analyses of these bi-dimensional projections, soon the lack of information from the third dimension emerged and a number of subsequent pioneer studies addressed this absence of data through very elegant experiments in which hippocampal synapses and spines were reconstructed thanks to the acquisition of stacks of independent images from TEM serial sections [34] [8,35]

Summary

Introduction

The concept of the dendritic spine has undergone evolution since their discovery by the neuroanatomist Ramon Y Cajal, in 1888, who observed by means of light microscopy “thin protrusions” on the surface of a number of Golgi-impregnated neurons. These thin structures were further characterized by Gray in 1959 [1], through electron microscopy (EM) investigations, as the major postsynaptic target of excitatory synapses in the central nervous system (CNS). Dendritic spine number is highly variable as at different ages synaptic establishment and pruning compete and experience can heavily affect formation of new spines, as well as spine maintenance

Objectives

Methods

Results

Conclusion