Neuroglia at the crossroads of homoeostasis, metabolism and signalling: evolution of the concept

Abstract

Ever since Rudolf Virchow in 1858 publicly announced his apprehension of neuroglia being a true connective substance, this concept has been evolving to encompass a heterogeneous population of cells with various forms and functions. We briefly compare the 19th-20th century perspectives on neuroglia with the up-to-date view of these cells as an integral, and possibly integrating, component of brain metabolism and signalling in heath and disease. We conclude that the unifying property of otherwise diverse functions of various neuroglial cell sub-types is to maintain brain homoeostasis at different levels, from whole organ to molecular.

Figure 1. Early 20th century survey of glial biology in medicine: form and function

(A) Camillo Golgi's drawings of astrocytes contacting blood vessels (from Golgi, 1903). (B) The close envelopment of neurons by the processes of neuroglial cells as seen by Santiago Ramón y Cajal (redrawn from Cajal's original plate by De Castro, from Glees, 1955). (C) Morphological diversity of neuroglia in human fetal cortex (Retzius, 1894–1916, Vol. 6, Plate II, Figure 5). (D) Close interactions between neuroglial (red) and neuronal (black) networks (from Schleich, 1894). (E) Oligodendroglia of the white matter and one astrocyte with a vascular endfoot showing the distribution of darkly stained granules or gliosomes in their processes (from Penfield, 1924), the image is taken from Glees (1955). (F) Pathological potential of neuroglia. The drawing by Alois Alzheimer (Alzheimer, 1910) shows association of glial cells (glz) with pathologically modified neurons (gaz or ganglion cells).