Regulation of microglia by neuromodulators: Modulations in major and minor modes

Microglial cells, the brain resident macrophages, participate to brain development and function and help maintaining its homeostasis. To play these roles, they need to detect and adapt to modifications of their environment, including changes in the activity of neurons. The neuromodulators serotonin, dopamine, norepinephrine, acetylcholine and histamine are synthesized and released by specialized neurons to coordinate the activity of other neurons in different regions. In this review, we summarize the current evidence obtained in vitro or in vivo that neuromodulators act on microglia. On the short term, they can modify their motility, morphology and phagocytic activity; on the mid-long term they can modulate their transition between different immune activation states. Lastly, we review some recent data suggesting that these regulations of microglia by neuromodulators are involved in vivo in some aspects of central nervous system development, function and homeostasis.