Colitis-associated intestinal microbiota regulates brain glycine and host behavior in mice

Abstract

Inflammatory bowel diseases (IBD) are chronic and relapsing inflammatory disorders of the gastrointestinal tract with complex etiology and no strategies for complete cure. IBD are often complicated by mental disorders like anxiety and depression, indicating substantial shifts in the gut-brain axis. However, the mechanisms connecting IBD to mental diseases are still under debate. Here we use Muc2 mutant mouse model of chronic colitis to uncouple the effects of the intestinal microbiota on host behavior from chronic inflammation in the gut. Muc2 mutant male mice exhibit high exploratory activity, reduced anxiety-related behaviors, impaired sensorimotor gating, and altered social preference towards males and females. Microbial transfer to wild-type mice via littermate co-housing shows that colitis-associated microbiota rather than inflammation per se defines behavioral features in Muc2 colitis model. Metagenomic profiling and combination of antibiotic treatments revealed that bacterial species Akkermansia muciniphila is associated with the behavioral phenotype in mutants, and that its intestinal abundance correlates with social preference towards males. Metabolomic analysis together with pharmacological inhibition of Gly and NMDA receptors helped us to determine that brain glycine is responsible for the behavioral phenotype in Muc2 mice. Blood and brain metabolic profiles suggest that microbiota-dependent changes in choline metabolism might be involved in regulation of central glycine neurotransmission. Taken together, our data demonstrates that colitis-associated microbiota controls anxiety, sensorimotor gating and social behavior via metabolic regulation of the brain glycinergic system, providing new venues to combat neurological complications of IBD.

Investigating social communication in mice: A two‐intruders test approach

“…To reduce labor, cost and animal misuse, we prefer intact naïve males as intruders, so that they can be used later in other experiments. Our results demonstrate that both BALB/c and C57BL/6 mice are suitable for the two-intruders test as male intruders (Figures 1 and 3), which agrees with the results obtained earlier (Morozova et al, 2022). Moreover, BALB/c intruders provoke efficient response in the resident-intruder assay (Amstislavskaya & Khrapova, 2002;Amstislavskaya & Novikov, 2018;Novikov, 1988).…”

“…The two-intruders test reported in this study is based on the previously described mating choice assays and our own design published earlier (Amstislavskaya et al, 2013;Koolhaas et al, 2013;Kuznetsova et al, 2006;Leypold et al, 2002;Liu et al, 2011;Morozova et al, 2022;Norlin et al, 2003). For instance, Leypold (Leypold et al, 2002), the authors define this experimental paradigm as a "mating choice test" since it reflects increased sexual behavior toward male intruders in trp2 mutants.…”

“…By recording the frequencies, durations, latencies, and temporal and sequential patterns of all the observed behavioral acts, a detailed quantitative picture resident and also intruder behaviors can be obtained. Thus, a number of studies describe interaction with a male and a female in a resident-intruder paradigm in mice in different settings (Belousova et al, 2009;Kuznetsova et al, 2006;Leypold et al, 2002;Liu et al, 2011;Morozova et al, 2022;Norlin et al, 2003;Zinck & Lima, 2013). However, given the competitive and mutually repressive nature of male-and female-derived cues processing in the animal brain, simultaneous interaction with animals of both sexes better represents social communication as it occurs in a natural environment.…”