We see that depletion of the gut microbiota caused enhanced sensitivity to the rewarding and sensitizing properties of cocaine (Fig. 3). This represents the first report that alterations to the gut microbiome can affect behavioral response to psychostimulant drugs. Previous studies on the effect of the gut microbiome on behavior have focused primarily on models of anxiety and depression562233. While there is clearly overlap between mood/anxiety and substance use disorders1415, characterization of how gut microbes can directly affect drug-related behavior represents an important step forward. A series of studies has shown that a subset of patients with alcoholism have increased gut dysbiosis and that this is associated with increased depressive symptoms and cravings to drink3435. While this does provide compelling evidence of a correlation between gut dysbiosis and alcohol action, studies providing a direct examination of the two have yet to be published. The changes we see in the altered sensitivity to rewarding and sensitizing effects of cocaine are important, as they suggest that alterations in gut bacteria can change cocaine-related behaviors. There is already one study in humans demonstrating
