GLAM: Glycogen-derived Lactate Absorption Map for visual analysis of dense and sparse surface reconstructions of rodent brain structures on desktop systems and virtual environments

Human brain accounts for about one hundred billion neurons, but they
cannot work properly without ultrastructural and metabolic support. For
this reason, mammalian brains host another type of cells called “glial
cells”, whose role is to maintain proper conditions for efficient neuronal
function. One type of glial cell, astrocytes, are involved in particular
in the metabolic support of neurons, by feeding them with lactate, one
byproduct of glucose metabolism that they can take up from blood vessels,
and store it under another form, glycogen granules. These energy-storage
molecules, whose morphology resembles to spheres with a diameter ranging
10–80 nanometers roughly, can be easily recognized using electron
microscopy, the only technique whose resolution is high enough to resolve
them. Understanding and quantifying their distribution is of particular
relevance for neuroscientists, in order to understand where and when
neurons use energy under this form. To answer this question, we developed
a visualization technique, dubbed GLAM (Glycogen-derived Lactate
Absorption Map), and customized for the analysis of the interaction of
astrocytic glycogen on surrounding neurites in order to formulate
hypotheses on the energy absorption mechanisms. The method integrates
high-resolution surface reconstruction of neurites, astrocytes, and the
energy sources in form of glycogen granules from different automated
serial electron microscopy methods, like focused ion beam scanning
electron microscopy (FIB-SEM) or serial block face electron microscopy
(SBEM), together with an absorption map computed as a radiance transfer
mechanism. The resulting visual representation provides an immediate and
comprehensible illustration of the areas in which the probability of
lactate shuttling is higher. The computed dataset can be then explored and
quantified in a 3D space, either using 3D modeling software or virtual
reality environments. Domain scientists have evaluated the technique by
either using the computed maps for formulating functional hypotheses or
for planning sparse reconstructions to avoid excessive occlusion.
Furthermore, we conducted a pioneering user study showing that immersive
VR setups can ease the investigation of the areas of interest and the
analysis of the absorption patterns in the cellular structures.