The structure of astrocytes is likely to shape the interaction between neurons and astrocytes in the brain. It is intuitive that astrocytes processes close to a synapse can more effectively modify synapse function than distant processes. Mike Stewart’s lab at Milton Keynes has now demonstrated in collaboration with us that astrocyte processes cover thin neuronal spines receiving excitatory input more than bigger spines, so called mushroom spines (Phil. Trans. R. Soc. B, link). This is of particular interest because thin spines are widely believed to represent spines at which long-term potentiation (LTP, the potential cellular mechanism of learning) has not occurred yet. It might suggest that these spines are particularly well protected from spill-in of neurotransmitter from neighboring synapses.
In a separate study we were wondering if morphology of whole astrocytes is heterogeneous within a brain region. Using fluorescence imaging in brain slices we could reveal that brain regions occupied by individual astrocytes can be oriented along principal cell dendrites (hippocampus, CA1 region). A subset of these cells had a morphology that could promote intracellular diffusion along along principal cell dendrites. Indeed astrocyte coupling, a key feature of astrocyte networks, was anisotropic and more pronounced along the same axis (Phil. Trans. R. Soc. B., link). These observations imply that astrocyte morphology determines spread of a diffusible signal within a gap junction coupled astrocyte network and can give it a directionality.
… and of course congratulations to all authors.