Title:

Can Mice Help Us Understand the Role of the Gut Microbiome in Risk of Opioid Abuse?

Despite the well-established role of the microbiome in shaping behavior through the gut- microbiome-brain axis, and the dramatic gut dysbiosis caused by opioids, studies linking variation in the gut microbiome to drug abuse liability are lacking. We used mice that vary individually in their drug seeking behavior to investigate correlations between the microbiome and compulsive drug use. Our study objectives were to 1) establish how individual microbiomes vary in response to morphine and 2) to establish whether composition or responses to morphine vary between individuals. The microbiomes obtained from fecal material of five individually housed mice trained on operant procedures were surveyed as the mice transitioned from chow, to chow plus supplemental self-administration of sucrose, and finally to chow plus morphine in sucrose solution. Microbiome profiles were determined through 16S rDNA V4-V5 amplicon sequencing and morphine induced changes were examined using tools in the QIIME 2 pipeline. Community diversity decreased with sucrose consumption, and microbiomes shifted into several clusters reflecting the reduction of different species. In contrast, morphine use increased diversity. Importantly, we did find individual variability in microbiome response to morphine. For example, although the genus abundance of nearly all mice shifted in response to both sucrose and morphine, the composition of individual mice differed from each other and one mouse microbiome exhibited little change post morphine. Specifically, abundance of the probiotic bacteria Bifidobacterium decreased while potentially pathogenic Clostridium species increased in nearly all post-morphine gut microbiomes, mirroring changes previously reported in humans. Turibacter and Roseburia species increased in some mice, whereas other mice had a decrease in Anaeroplasma species. These data suggest that different exposures may shift the gut microbiome, and that there is individual variation in response.

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