THE MICROBIOTA-GUT-BRAIN AXIS The Microbiota-Gut-Brain Axis. Physiol Rev 99: 1877–2013, 2019. Published August 28, 2019; doi:10.1152/physrev.00018.2018.—The importance of the gut-brain axis in maintaining homeostasis has long been appreciated. However, the past 15 yr have seen the emergence of the microbiota (the trillions of microorganisms within and on our bodies) as one of the key regulators...