Design-Based Stereology in Brain Aging Research

Abstract

In recent years, the application of design-based stereologic methods to the analysis of the central nervous system has contributed considerably to our understanding of the functional and pathological morphology of the aging brain. Design-based stereology has become the method of choice in quantitative histological analysis. Its advantages over other quantitative techniques in respect to rigor, accuracy, and consistency of results have been documented extensively in the scientific literature.Originally, design-based stereology was described as a set of methods that provide a three-dimensional interpretation of structures based on observations made on two-dimensional sections [1]. However, in the current use of design-based stereology, many methods make use of three-dimensional sections. The term “design-based” indicates that the methods and the sampling schemes that define the newer methods in stereology are “designed,” that is, defined a priori, in such a manner that one need not take into consideration the size, shape, spatial orientation, and spatial distribution of the cells to be investigated [2]. Eliminating the need for information about the geometry of the cells under investigation results in more robust data because potential sources of systematic errors in the calculations are eliminated [2–4].Design-based stereology can be divided into analyses of the global and local characteristics of tissues, the most important of which are volume, number, connectivity, spatial distribution, and length of linear biological structures. These characteristics can be expressed as absolute values (e.g., the volume of the granule cell layer in the human hippocampus, the number of granule cells in the human hippocampal granule cell layer, etc.) or as relative values (e.g., the volume fraction of the human hippocampus occupied by the granule cell layer, the density of granule cells within the human hippocampal granule cell layer, etc.). Both global and local characteristics can be analyzed by a variety of stereologic methods.This chapter is divided into three parts. The first part provides an overview of recent progress in brain aging research on humans, non-human primates, and rodents with design-based stereology and reviews the main outcome of such investigations. The second part of the chapter provides an introduction into the use of design-based stereologic methods that most neuroscientists interested in their use would need to analyze volumes of brain regions, numbers of cells (neurons, glial cells) within these brain regions, mean volumes (nuclear, perikaryal) of these cells, length densities of linear biological structures such as vessels and nerve fibers, and the cytoarchitecture of brain regions (i.e., the spatial distribution of cells within a region of interest). The chapter closes with a short outlook on the future of design-based stereology in brain aging research.