Astrocytes, star-shaped glial cells, are the most abundant glial cell type in the central nervous system (CNS). They play a crucial role in maintaining brain homeostasis, regulating synaptic activity, supporting neuronal metabolism, and responding to injury. Their diverse roles highlight their importance in both healthy brain function and various neurological disorders.

Astrocytes have branches extending from their soma, which divide into smaller structures called branchlets, lamelliform perisynaptic astrocytic processes (PAPs), and endfeet. Due to the nanometric size of these structures, electron microscopy (EM) is the only technique capable of fully imaging astrocytes, revealing their spatial distribution, heterogeneity, and synaptic coverage. Understanding astrocyte ultrastructure is vital for advancing knowledge of the CNS in health and disease.

The recently published research delves into the scientific literature on the three-dimensional ultrastructure of astrocytes in the CNS, spanning from the 1960s to the present. While volume electron microscopy (vEM) gained momentum in this area in the 2000s – due to advancements in automated sectioning and backscattered electron sensors – serial section EM and 3D reconstructions were already present in the 1950s. The study provides a comprehensive overview of astrocyte ultrastructure across brain regions, species, and imaging techniques – bridging knowledge gaps and supporting researchers in structural biology and computational neuroscience.