Rapid modulation of gut microbiota composition by hypothalamic circuits in mice.

In recent years, the gut microbiota and derived metabolites have emerged as relevant players in modulating several brain functions, including energy balance control. This form of distant communication mirrors that of metabolic hormones (e.g., leptin, ghrelin), that convey information about the organism's energy status by exerting effects on diverse brain regions including the master homeostatic centre the hypothalamus. However, whether the hypothalamus is also able to influence gut microbiota composition remains enigmatic. Here, we present a proof-of-concept study designed to unravel this challenging question. To this aim, we employed chemogenetics (to selectively activate or inhibit the activity of hypothalamic POMC or AgRP neurons) or administered leptin or ghrelin centrally to mice. Subsequently, we conducted microbiota composition analysis throughout the gut using 16S rRNA gene sequencing. Our results showed that these brain interventions significantly changed the gut microbiota in an anatomical and short-term (2-4h) fashion. Transcriptomic analysis indicated that these changes were associated with the reconfiguration of neuronal and synaptic pathways in the duodenum concomitant with increased sympathetic tone. Interestingly, diet-induced obesity attenuated brain-mediated changes induced by leptin in gut microbiota communities and sympathetic activation. Our findings reveal a novel and unanticipated brain-to-gut axis that acutely attunes microbiota composition at fast timescales, with potential implications for meal-to-meal adjustments and systemic energy balance control. C57BL/6 male mice at 8 weeks of age were anesthetized and a stainless cannula was implanted in the right lateral ventricle. One day post-surgery, mice were divided into water or antibiotic treatment (ampicillin 1 g/L; neomycin 0.5 g/L in drinking water) groups. Following this treatment for 48h, either saline or leptin (3 µg) was delivered ICV and the mice were sacrificed 2 hours later. The duodenum was harvested and snap-frozen in liquid nitrogen. Frozen samples were processed for RNA isolation and subsequent RNA sequencing was performed. Duodenal mRNA was isolated using Trizol (Invitrogen) following standard protocols. Quantification and integrity analysis of total RNA were performed by analysing 1 μl of each sample in an Agilent 2100 Bioanalyzer (Agilent RNA 6000 Nano Kit; Agilent). Total RNA strand-specific RNA libraries were generated using 150 ng of total RNA with the Illumina® Stranded RNA Prep Ligation kit with RiboZero Plus following the manufacturer’s instructions. Libraries were sequenced on an Illumina NextSeq2000 (Illumina, Inc.) in paired-end mode with a read length of 2×50 bp.