Immune cells called microglia help to protect the brain after an injury. They may also be involved in pruning the connections, or synapses, between neurons — a key process in learning and memory formation.
Using electron microscopy, Marie-Ève Tremblay, Rebecca Lowery and Ania Majewska at the University of Rochester in New York imaged mouse brain slices and reconstructed the interactions between microglia and synapses in three dimensions. Most of the microglia were directly adjacent to the synapses, and in particular to dendritic spines — neuronal structures — that were small and were often pruned away later on.
The authors also subjected mice to shifts in visual experience using light deprivation and re-exposure. After this regime, some microglia more often displayed features that allow them to engulf synaptic elements, suggesting a role for these cells in trimming back synapses after new experiences.