Structure and interactions of glial cells and neurons in a basal ganglia connectome

Glial cells show great diversity and differ in terms of their functional roles. Microglia, oligodendrocytes, and astrocytes interact with neurons and thus ensure the functionality of the neurons. However, little is known about how they interact with different neuronal cell types. We investigate glial and neuronal interactions in a connectomic dataset with a resolution that enables us to see synapses and subcellular structures. Our area X dataset, a singing-related basal ganglia nucleus, in the zebra finch contains thousands of neurons and a million synapses and different glial cell types: astrocytes, microglia and oligodendrocytes.Morphological analysis of the three glial cell types fit with descriptions from the literature, for microglia putative resting and activated forms were identified. In addition to the expected glial cell types, migrating neurons were also identified. Further analysis of the nanoarchitecture of astrocytes showed specific regions as described in Salmon et al., 2023. In regard to subcellular structures, the mitochondrial volume density was analyzed. There, astrocytes show a high mitochondrial volume density, similar to very active neurons in area X, leading to further investigation of energy supply. Mitochondrial size in all glial cell types seems to depend more on the cell compartment than on the distance to the blood vessels of the brain. Investigating contact areas between glial and neuronal cell types as proxy for potential interactions showed preferences for specific neuronal cell types.Our work highlights the advantages of using connectomics to study glial cells and their interactions with neurons to support further in vivo analysis.