Visual analysis of glycogen derived lactate absorption in dense and sparse surface reconstructions of rodent brain structures

Astrocytes are the most abundant type of glial cells of the central nervous system; their involvement in brain functioning, from synaptic to network level, is to date a matter of intense research. A well-established function of astroglial cells, among others, is the metabolic support of neurons. Recently, it has been shown that during tasks like learning and long-term memory formation, synapses sustain their metabolic needs using lactate, a compound that astrocytes can synthesize from glycogen, a molecule that stores glucose, rather than glucose itself. Aforementioned role of astrocytes, as energy reservoir to neurons, is challenging the classic paradigms of neuro-energetic research. Understanding their morphology at nano-scale resolution is therefore a fundamental research challenge with enormous implications on many branches of neuroscience research, such as the study of neuro-degenerative and cognitive disorders. Here, we present an illustrative visualization technique 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 a high-resolution surface reconstruction of neurites and the energy sources in form of glycogen granules, and computes an absorption map according to a radiance transfer mechanism. The technique is built on top of a framework for processing and rendering triangulated surface models, and it is used for real-time 3D exploration and inspection of the neural structures paired with the energy sources. The resulting visual representation provides an immediate and comprehensible illustration of the areas in which the probability of lactate shuttling is higher. This method has been further employed for testing neuroenergetics hypotheses about the utilization of glycogen during synaptic development.