Synaptic Pruning by Microglia Is Necessary for Normal Brain Development

From Mildner et al. 2008 

Image from Mildner et al.2008.Microglia expressing GFP and surrounding a neuron (in red).                    

Microglia have been shown to be extremely dynamic after insult to the nervous system (they are very good at clearing damaged cellular debris for example). However it remains less clear what role microglia play in physiological conditions. Recent findings published this month in Science reveal an incredible role for the little monocytic cells in synaptic maturation in the brain. Just like garderners, microglia prune the connections between neurons shaping how the brain is wired. Impressive!  From sciencedaily.com

Looking at the developing mouse brain under the microscope, Gross and colleagues found proteins from synapses — the connections between neurons — inside microglia, indicating that microglia are able to engulf synapses too.

To probe further, the scientists introduced a mutation that reduced the number of microglia in the developing mouse brain.

"What we saw was similar to what others have seen in at least some cases of autism in humans: many more connections between neurons," Gross says. "So we should be aware that changes in how microglia work might be a major factor in neurodevelopmental disorders that have altered brain wiring."

The microglia-limiting mutation the EMBL scientists used has only temporary effects, so eventually the number of microglia increases and the mouse brain establishes the right connections. However, this happens later in development than it normally would, and Gross and colleagues would now like to find out if that delay has long-term consequences. Does it affect the behaviour of the mice behaviour, for example? At the same time, Gross and colleagues plan to investigate what microglia do in the healthy adult brain, where their role is essentially unknown.

This work was carried out in collaboration with the groups of Davide Ragozzino at the University of Rome and Maurizio Giustetto and Patrizia Panzanelli at the University of Turin.

Read the original article by Gross and colleagues here