Microglia morphology in the physiological and diseased brain - from fixed tissue to in vivo conditions.

First mentioned almost 100 years ago, neuroresearch has linked microglia to the initiation and/or maintenance of most central nervous system pathologies. Since their discovery, we learned that the microglia immune status is often correlated directly to their morphology. However, only recently, have we realized that, in vivo microglia are extremely dynamic cells capable to respond within minutes. Therefore, the name "resting" microglia is replaced slowly with surveilling microglia. Even more recent, it has been shown that microglia change their morphology and/or immune status depending on the way the tissue is obtained, processed and imaged, making labeling microglia, based on their morphology alone, as active or surveying even more difficult. All these observations correlated with a better understanding of cellular and subcellular process that microglia undergo in pathological conditions, could have profound implications on the time window and/or targets used to ensure the best outcome, when treating brain disease.