Scientific Understanding of Consciousness
Consciousness as an Emergent Property of Thalamocortical Activity

Microglia crucial for Pruning Neurons during Development



Nature 485, 570–572  (31 May 2012)

Microglia seem crucial for Pruning Back Neurons during Development

Virginia Hughes -- a freelance science writer in New York City


For more than a century, neurons have been the stars of neuroscience. But they account for only about 10% of the cells in the human brain. The balance is made up by different types of glia, which surround and support neurons and influence neuronal signalling. Oligodendrocytes, for example, create fatty sheaths that encase long neuronal branches and help to speed up electrical impulses. Astrocytes surround synapses and have been shown to affect neuronal signalling by controlling the mix of chemical messengers at neuronal junctions.

Microglia are quite different from their neighbours. Unlike neurons and other glial cells, they begin in the embryonic yolk sac as immune-cell progenitors, just as the macrophages that patrol the bloodstream for foreign invaders do. During prenatal development — within eight embryonic days in a mouse — microglia migrate to the brain, where they become its dedicated immune cells. Researchers assume that the brain needs microglia because the blood–brain barrier seals it off not only from toxins, pathogens and some drugs in the bloodstream, but also from the immune cells circulating there.

Microglia spring into action in most brain diseases, engulfing pathogens, dead cells and misfolded proteins. They also clear away synapses that have been damaged by injury. It is not a big intellectual leap, then, to suppose that microglia have similar roles in the healthy brain. Microglia cells are probably extremely important for synapse remodelling and plasticity in development.

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